Garden Displays Ltd

Eco-Book

Appreciating Garden Biodiversity

from an Ecological and Evolutionary perspective

This text puts the terms biodiversity, ecology and the greatly connected word evolution into context. This allows the environmentally conscious gardener to have a comprehensive overview from an evolutionary ecological stand point. It is hoped this will lead to an increased wish to follow more sustainable and eco-friendly practices.  It continues  to provide relevant information on typical organisms associated with common garden plants and their role in the garden food web.

I hope you enjoy the read and enjoy gardening; always with biodiversity first in mind.

 

Why ecologically based gardening?

Wildlife friendly, organic, no dig, re-wilding and naturalistic styles are all labels of practices gaining increasing popularity with garden owners . They are all underpinned by a recognition and understanding of ecology, biodiversity, sustainability and protecting past and present evolution. How well is the importance of these words truly understood and appreciated. The aim of this Eco-book is to provide a dip in resource, to be revisited many times, by the eco-conscious gardener wanting to acquire a comprehensive understanding and develop a greater respect and enthusiasm to protect, restore and enhance the natural processes of their garden and the wider environment.

First impressions of the text may be that I have delved in too deep but read on as it is all relevant and important to know because we are all connected with nature. As the biology professor David Goulson has stated "We are part of nature not apart from nature.’ Our actions today will effect the actions and inheritance of future generations. Although lengthy, it is still a considerably shortened account of the broadly consensual understanding  and agreement of the scientific establishment. It covers 4.54 billion years, taking into consideration the pace of evolution and identifies organisms still extant today that first appeared billions of years ago. Perfectly suited to their habitat they have not needed to evolve further but their presence is  a critical cog in the engine of biodiversity and gives us a real time insight into early life forms on Earth. In realising this we understand the importance  of not interfering with natural evolutionary processes too much.

Humans have already unbalanced the natural equilibrium of their planet through over exploitation of fossil fuels, deforestation and climate change being obvious examples.This text will make the reader realise how important it is we do not upset the balance further and indeed the importance of attempting to rebalance  elements where possible such as reforestation and other practices that would rectify global warming etc. The  undertaking of any practice or synthesis of any man made product which is reproduced on a global scale risks continuing the unbalancing of the equilibrium of the natural world further Every one of us has a duty of care to protect our immediate natural environment as well as consider the long term and wider global implications of our actions. This ethical duty which is easier for one person such as a garden owner taking the bold step of avoiding herbicide use and  proudly accepting nature’s ‘untidiness’ will be more difficult for the landscape manager trying to balance ethical and client demands. My aim is to promote, practice and push for acceptance and desire for eco-friendly garden & grounds landscaping and maintenance practices,

Where  possible I have tried to avoid providing too many numbers and percentages from scientific study although current hypotheses (agreed by many scientists but not all) are unavoidable to attain a comprehensive understanding of evolutionary  ecology in context.  Hypotheses once published  are often invariably criticised by other scientists. The problem is scientists  and other experts cannot  unreservedly agree with one another on subjects such as evolution, global fossil fuel depletion, climate change , harmfulness of pesticides etc. The publication of one academic paper is quickly challenged by the publication of another, usually actioned by the product manufacturer, refuting the evidence and arguing methodology of data collection flaws etc. This results in ongoing debates and confusion not only of experts but  more importantly for the masses of  lay persons (in our case gardeners)  wanting accurate facts to know we are doing the right thing . The information that follows is what I believe to be the most accurate independent, least biased, evidence based principles agreed by most impartial experts and place them in a logical sequence to follow. I am however open to enlightenment and greater education so please feel free to contact me to improve this works.

 

The abundance of life (biodiversity) on Earth

Here comes the first paragraph containing  percentages, numbers and hypotheses . Scientific study suggests that probably more than 99% of animal, plant, fungi etc species have become extinct since the beginning of life with present day estimates suggesting  there are currently between 10-14 million species on Earth; of which only around 1.2 million having been identified.  A 2016 study suggested  there are around a further 1 tillion microbial species to be discovered and identified. The unidentified organisms are largely microscopic invertebrates or as yet poorly studied organisms which are found in habitats that have not been fully explored and studied such as remote parts of rainforests and deep ocean floors. Extinction caused by human activities primarily land use change such as deforestation for large scale food production, over exploitation such as fishing and harvesting as well as factors  accelerating climate change are all contributing to biodiversity loss. Estimates of decline are always challenged some estimates paint a bleaker picture than others , what ever the numbers or percentages, they are large.

 

All these organisms extant and extinct share similarities which many scientists think suggests a common (single or very few) ancestor(s) linking all living and extinct organisms whether plant, animal, fungi etc. This is known as the Last Universal Common Ancestor or LUCA hypothesis. It is demonstrated through a  phylogenetic tree, or tree of life. A pictorial tool used by biologists to show the  evolutionary relationships among all forms of life on Earth. So,  if we think of ourselves and then think back to our parents and back further to our  grand parents and then onto our great grand parents etc and keep going back continuously through time as diversity diminishes towards the beginning of life on Earth we would come to the point where life began and that everything forward from that point has one or small number of  universal common ancestor (s).The LUCA hypothesis, more on this later.

 

For most people the practice of eco-friendly or wildlife gardening focuses on an awareness of biodiversity but with the larger, more visible and often attractive animals such as bees, butterflies, birds and animals such as hedgehogs given greatest attention.  Often only briefly mentioned sometimes ignored is the importance and vast abundance of mainly microscopic decomposers. These detrivores are believed to make up 70% biomass of organisms globally.  I intend to bring them much more into the focus of attention because without them our ecosystems would collapse. Although we cannot see most of them (without magnifying glasses or appropriate microscopes) they are there and the importance of their presence should  be given equal status to the birds, bees, butterfly’s etc.  Considering that many traditional garden practices; the use of chemicals to control weeds, pests & diseases and plant fertilisers have a negative impact on the many organisms present in the garden, habitat biodiversity is remarkably resilient, recovering quickly or at least maintaining a presence, most noticeable in our gardens seen by the annual decomposition of organic matter such as fallen leaves.

 

Ecology defined

Depending on the scholarly texts read there can be  slight variation on emphasis on precise definition.Such as the definition given by ecologists Robert Ricklefs  & Rick  Relyea  (2014) as ‘the scientific study of  the abundance and distribution of organisms in relation to other organisms and environmental conditions.’

In simple lay person terms it is the study of the complex interactions and relationships between living (and dead) organisms and their non- living  physical environment, put another way the interactions and relationships between the biotic and abiotic environment. Microscopically this includes the atoms which form molecules which give rise to all living micro and macro -organisms and also the non living physical elements which make up the environment; land, sea and air.

Ecology is interwoven and inseparable from other specialist disciplines such as entomology, zoology, geology, biology, chemistry, horticulture and agriculture and numerous other disciplines.

In the garden setting the physical environment is what the soil structure is composed of such as minerals, organic matter and water levels together with the macro and micro climate; seasonal temperatures, air and light quality, wind, periods of snow etc. The living organisms within and on the soil surface as well as on and within other organisms make up 7 kingdoms recognised and proposed by Thomas Cavalier- Smith ( 1942-2021, Professor of evolutionary biology at University of Oxford). These are plants, animals, fungi, bacteria, archaea, protozoa and Chromista. All of which make up biodiversity.

Darwinism and Neo Darwinism

The huge numbers of species and subspecies that have evolved or become extinct on Earth through epochs of time driven by survival of the fittest make up the Darwinian concept of evolution through natural selection. Although Charles Darwin (1809-1882) is credited with the theory of evolution of species diversity, historical records show  numerous other people were working on the theory of natural selection at the time such as the British naturalist Alfred Russel Wallace (1823-1913). However,  Darwin had the resources and connections to publish and promote his work. Although greatly accepted by the scientific community the Darwin evolutionary theory of gradual accumulation of small biological changes tracking prevailing environmental conditions was not accepted by all. Especially strongly religious people.

Most of the scientific community at the time believed in the theory of  directed progressive evolution or orthogenesis. This theory suggested that the incremental evolutionary changes or modifications leading to more complex organisms follows a set direction and is not influenced by chance events known as punctuated evolution or equilibrium. This latter theory poposes that evolution is composed of long periods of evolutionary stasis during which no or perhaps only a few changes take place intermixed by punctuated periods characterised by dramatic jumps of evolutionary change.

Darwin did not fully understand the mechanism by which mutations occur. The mechanisms of genetic change and inheritance was poorly understood and greatly debated amongst scholars of the time. It was not until later that scientific works provided the evidence to  support Darwin’s theory. The Austrian monk Gregor Mendel (1882-1884),  the father of genetics is credited with the first works which paved the way towards the modern day understanding of genetics eventually supporting  Darwin’s theory. It was not until the 1930’s that research by Ronald Fisher (1890-1962), John B. S. Haldane (1892-1964) and Sewell Wright (1889-1988) provided the supportive proof of Mendel’s work. They applied Mathematical principles to Mendel’s genetic theory and proved that the inheritance of genes mirrored the variation of characteristics  seen in populations.

The species that survive and evolve are fitter by having better adapted characteristics through genetic and chromosomal mutations to exploit  the prevalent evolving and changing  environment.  Both the physical abiotic environment and organic biotic competitors, prey and predators they share their environment with influence an organism’s ability to continue existing through genetic mutations. This modern understanding of the theory of evolution now known as neo-Darwinism  was written by the British evolutionary biologist Sir Julian Huxley (1887-1975) in his 1942 book 'Evolution: The Modern Synthesis'.

Darwin also did not believe that sudden changes in the fossil record were down to random mass extinctions and that the fossil record was merely incomplete. Mass extinctions through meteorite impacts and climate changes have now been shown to have caused these sudden changes in the fossil record. Mass extinction events do not favour one organism over another. A catastrophic event will wipe out everything in its path. Both poor and fit organisms will perish in a catastrophic event. Those that survive will survive through luck or chance. A poor competitor may survive an event which eradicates a stronger competitor  resulting in it becoming  the better adapted to the new environment and in turn the stronger competitor . Although scientific debate is not fully resolved it seems that both incremental and punctuated changes play roles in species evolution.

Life on Earth is  still constantly evolving. Biodiversity in evolutionary ecology describes this abundant and complex evolution of past life which has lead to the huge variety of life on earth today. Present day  biodiversity on Earth  is studied on three different levels,  ecosystem diversity, species diversity and genetic variability. As eco gardeners we are mainly concerned with the importance of appreciating and maintaining ecosystem biodiversity. To allow the present day natural balanced associations and interactions between all living organisms and abiotic factors to continue and keeping human interference to a minimum.

Comparing present day extinction rates with past extinctions rates as seen from fossil records strongly suggests that extinctions are fast exceeding previous rates. Some studies suggest extinction rates anywhere between 10 and 100 times faster than pre human times. An Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem services (IPBES) estimates that around one million plants and animals threatened with extinction.

Biodiversity

Biodiversity is the term used to encompass all living things on Earth. Since 2015, they are 7 recognised kingdoms proposed by Thomas Cavalier- Smith and accepted by many scholars. With ongoing advances in scientific knowledge,  new organisms and metabolic organisations are continuously being identified which will probably  result  in further reclassification of kingdoms.

 

1. Plant kingdom: Consisting of predominantly photosynthetic (some have carnivorous ability, such as sundew, Drosera spp and pitcher plants eg Nepenthes spp) multicellular eukaryotes (genetic DNA contained in nucleus in cell). Photosynthesis occurs in organelles  called chloroplasts which obtain energy from the sun and synthesis of nutrients using water and carbon dioxide for growth with oxygen as a waste product.  The cells of eukaryote plants also have a cell wall with cellulose in its composition. In todays plants reproduction  tends to be sexual from seed production (most plants) or spores (as in ferns, mosses and liverworts). Reproduction can also be vegetatively asexual by producing stolons (above ground horizontal stems producing new plants at tip) or rhizomes (underground stems from which new plants are produced).

 

An interesting ecological interpretation of stolons and rhizomes  is that the ‘new young plants’ may not be intentionally designed to become unassociated and separate plants but an extension of the older plant looking to exploit new ground for resources. For example an older plant may find it’s position becoming too shady sending out growth to improve photosynthetic ability. Resources could in this way be shared,  the older plant part benefiting from new plant(s) photosynthetic location whilst the new plant  receives water from the older plants water uptake.

 

2. Animal kingdom: Animals are multicellular eukaryotic organisms, the cells contain a nucleus and other organelles but no  cell wall or chloroplasts. They tend to be mobile and reproduce sexually. Primary examples being larger mammals and much smaller insects. They are heterotrophic, obtaining their nutrition from complex organic substances living or dead as opposed to plants which tend to be autotrophic able to obtain nutrients from simple organic substances such as carbon dioxide. Animals also have a nervous system, consisting of the brain which sends signals via spinal cord and complex  network of nerves to  different parts of the organism.
3. Fungi kingdom; Fungi including yeasts and moulds contain characteristics found in both the animal and plant kingdoms. Their cell walls contain chitin which is a fibrous material made up of polysaccharides and also found in the cell walls of arthropods. Fungi do not contain chloroplasts so they are unable to photosynthesise. A characteristic shared with many plant species is that they  reproduce by spores. The multi cellular forms tend to be immobile producing hyphae which form a mycelial mat which resembles the root system of plants absorbing dissolved molecules for nutrition. Fungi are believed to have helped enable the transition of aquatic plants from the  primordial oceans to land.
4. Bacteria kingdom: Some times referred to as eubacteria. These  bacteria are single celled organisms. They have cell walls but their DNA is not bound by a nucleus and they do not contain any other organelles such as mitochondria etc. They are known as prokaryotes (before eukaryotes) they are among the first forms of life evolving around 4 billion years ago. They are extremely abundant and common decomposers in both terrestrial and aquatic habitats as well as disease causing agents.
5. Archaea kingdom: Sometimes referred to as archaebacteria. They are similar in appearance to single celled bacteria but with a different molecular organisation. They are believed to belong to an ancient group intermediate between bacteria and eukaryotes. They are usually found in in habitats with extreme conditions such as extremely high or low temperatures or very salty conditions.
6. Protozoa kingdom: Microscopic single celled eukaryotic animals. Their cell  DNA is enclosed in a membrane bound nucleus. Examples including amoebas, ciliates, sporozoans and flagellates. Originally and sometimes still grouped as Protista, but more often accepted as split into  Protozoa and Chromista  which have photosynthetic plastids.
7. Chromista kingdom: Single celled or multicellular eukaryotes which have plastids enabling photosynthesis,  examples include green, red and brown algae and diatoms.

Glancing back at the above list shows diminishing information on the above kingdoms. The much more visible and attractive plants and animals have the most information followed by fungi which are most noticible through their often colourful and structurally interesting above ground reproductive structures. The latter four kingdoms containing the smallest and  least visible organisms to the naked eye are much less considered and understood by most of us. However they are all critical components of a healthy ecosystem and their presence should be thought about in our every day appreciation and practices of wildlife gardening.

 

The general scientific consensus on how life first evolved

Fossil evidence  for the earliest forms of visible life  was first recorded in rocks from Wales during the 18th and 19th centuries in  which fossils could easily be seen and dated to around 570 million years ago. Another recent study suggests a more accurate date of around 543 mya. This period was named the Cambrian period after the Latin name for Wales. Darwin thought that these complex cellular fossils of extinct organisms could not have just appeared and must have been pre-dated by more soft bodied organisms that where not suited to fossilisation. Animal fossils were of greater interest than plant fossils so the eras referred to animals with ‘zoic’  endings rather than ‘Phytic’ endings which refer to plants. More on this later. This precursor period was known as the pre-Cambrian.

Modern microscopy advances now show that the pre -Cambrian period was packed with an abundance of early life, which was not visible to the early fossil hunters.They were mostly unicellular prokaryotes (cells without nucleus) similar in shape and internal organisation as todays cyanobacteria (blue green algae) and bacteria. Micro fossil evidence dates back, depending on literature read,  to between 3.8 and 3.7 billion years ago. This was a very long era without much change occurring in around 2 billion years. It is widely believed the nucleic acids and amino acids leading to present day life first evolved around 4 billion years ago.

The building blocks of life

My understanding of chemistry is limited but I have attempted to interpret knowledge of the complicated subject of evolutionary chemistry to the best of my ability in laypersons terms. Everything is made of atoms (eg hydrogen, oxygen, carbon etc are elements or pure substances made of atoms) Atoms are the smallest most basic units of elements and are made of the same  but different number and arrangement of three sub atomic particles protons, neutrons and electrons. When atoms combine they form molecules. For example  two hydrogen atoms can combine with an oxygen atom to form a water (H2O) molecule.  Numerous elements were present but life did not evolve till about 4 billion years ago.

The elements that were present 4 billion years ago in the atmosphere and primordial oceans were Nitogen (N2),  Hydrogen (H2) , carbon dioxide (CO2), methane (CH4) and ammonia (NH3). There was little or no free oxygen (O2). Most oxygen was combined with hydrogen  to form the primordial oceans. Free oxygen was in time  produced as a waste (or in modern terminology ‘bi’) product from early photosynthetic prokaryotes , the cyanobacteria. The theory of a  primordial soup was proposed in  1929 by John B. S. Haldane of the mathematical support to Mendel’s work fame as mentioned earlier. He proposed that within the primordial oceans water,  carbon dioxide methane and ammonia all came together in a hot dilute soup from which organic  sugars and amino acids, the building blocks of proteins where formed leading to the first  self replicating molecules. Methane and ammonia comprise carbon and nitrogen atoms bonded to different numbers of hydrogen atoms , CH4 and NH3 respectively. Haldane did concede that a Russian biochemist Alexander Oparin (1894- 1980) did reach this conclusion before him in 1924.

The self replicating systems of today are RNA and DNA and they provide the clues as to how the earliest self copying molecules began and support the Oparin-Haldane theories. . Stanley L Miller (1930-2007),  a post graduate student and his professor Harold Urey (1893- 1981) in 1953 performed an experiment at the University of Chicago using methane, ammonia and hydrogen molecules in a container of water simulating the early oceans and subjected it to UV electric lightening. This provided the energy as would have occurred by the suns UV radiation and discharges of lighting which would have been common 4 billion years ago before the ozone layer formed. The ozone layer is made of colourless gas comprising three oxygen (O3)  atoms and started to form when photosynthetic organisms started to produce oxygen as a waste or bi product. Ozone is formed when UV light breaks down an oxygen molecule to form two oxygen atoms each of which in turn bind with another oxygen (O2) molecule resulting in O3. I digress, the result of the Miller/Urey experiment was the formation of amino acid which are the organic building blocks of life which in turn form proteins. Subsequent experiments using other molecular elements believed to be in the primordial oceans, carbon dioxide, nitrogen and water vapour produced similar results including the formation of nucleotides which give rise to nucleic acids which form the self replicating systems RNA and DNA.

Abiogenesis is the study of original evolution of life and is a quite controversial subject as conditions between 4.5 billion to 4 billion years ago no longer exist. Some scientists  believe nucleic and amino acids can still be formed in certain oceanic conditions today but are consumed by micro-organisms which would not have been present at the time prior to life existing.

As mentioned the elements subjected to light energy experiments came together to form nucleic acids and amino acids. DNA and RNA are nucleic acids which encode genetic information required  by amino acids to make  proteins. These early RNA and DNA sequences were able to copy themselves and to direct protein synthesis. Although a very complicated subject requiring expert knowledge in chemistry in simple lay persons terms it is consensually agreed that the earliest prokaryote cells comprised self replicating RNA were able to copy themselves and control the synthesis of proteins. Oxygen, carbon and hydrogen molecules bonded to form lipid chains or membranes in which  interactions between nucleic acids and proteins could take place in a protected environment reasonably unaffected by external influences. Lipid molecules are smaller than protein molecules but it is estimated that there are around 50% more lipid molecules for every protein molecule in a cell membrane.

Early evolving prokaryotic bacteria and archaea respired anaerobically deep in the primordial oceans protected from deadly the UV  light of the sun. As mentioned 4 billion years ago the atmosphere contained  nitrogen  (N2), carbon dioxide (CO2) and small amounts of hydrogen (H2). The event of  the evolution of  prokaryotic cyanobacteria containing early photosynthetic organelles called plastids which in time evolved into chloroplasts, and their ability to photosynthesise resulted in oxygen as a waste or bi product.  This one evolutionary change resulted in ever increasing atmospheric oxygen which is  believed to have given to rise to the eukaryotes, the precursors of more complex animals which in turn have evolved in those extant today.

Oxygen being  a highly reactive gas was no good to the large numbers of  anaerobic bacteria most of which were poisoned . The greatly reduced  number, no longer able to breath in the higher oxygen levels of the atmosphere as today are restricted to hypoxia or oxygen deficient environments such as deep ocean floors but also inland lakes, rivers and swamps where agal scums can lead to depletion of oxygen as they die sinking to the bottom of the aquatic environments to decompose. Interestingly in humans the mouth and gastrointestinal tract are rich in anaerobic bacteria.

Ecological scientists take many clues from today which they believe demonstrate how things must have occurred billions of years ago. For example the green scum of blue green algae seen today in shallow stagnant ponds must have been similar to the conditions required billions of years ago for life to evolve and increase. Like today these environments must have been shallow and probably fairly motionless for life to have a chance to evolve and expand.

Rising  oxygen levels thus resulted in early anaerobic prokaryote cells changing their genetic organisation to a nucleus containing self replicating RNA and DNA which in turn gave rise to more complex nucleated aerobic pre-eukaryotic cells suited for specific metabolic pathways. Some contained ribosomes for protein synthesis, other pre- mitochondria suited for  respiration whilst others had pre-chloroplasts  for photosynthesis. These cells would have had specific efficiency advantages than earlier anaerobic prokaryote cells.

Fossil evidence suggests these complex pre-eukaryotes did not develop through genetic mutations but through single cells forming partnerships with pre-eukaryotic cells with different metabolic pathways. These initial combinations over time lead to intracellular symbiosis and in turn fused blurring the separate ancestry. Todays mitochondria and chloroplasts have different RNA and DNA from the cells in which they are found suggesting and supporting the theory that they were independent cells in the past. Animals cells are thought to have developed from pre-eukaryotic cells either not forming symbiotic relationships with pre-chloroplast pre-eukaryotic cells or by somehow loosing the pre-chloroplasts. Like todays protozoans these early single celled eukaryotes may have engulfed and consumed early photosynthetic plant cells. Such  present day clues reflecting possible events billions of years ago.

By the late pre-Cambrian there is fossil evidence of  multicellular eukaryotic animals or metazoans. Fossil remains of soft bodied animals lacking a skeleton resembling todays flat worm have been found in Edicaria Hills of Australia. These early animals are referred to as Edicarian a period showing soft bodied animals with no hard shell or skeleton. It is unclear if these animals are ancestors of jellyfish and sea anemones or an early evolutionary experiment that did not lead to any surviving animals extant today.

Life defined:

All organisms defined as living share certain characteristics. First they must be able to replicate or reproduce (sexually and/ or asexually), they must be also able to grow, feed, respire and excrete waste or produce a bi product which supports other life. For example bacterial breakdown of faeces which releases elements in a form absorbed by plants which in turn produce oxygen as a bi product of  photosynthesis which we breath etc.  Senses and mobility have been added to this but there are grey areas. Do viruses respire and so are they living ?(more on this later). Organisms use sensory systems to interpret their environments. Plants can grow towards light (sensory) but not move (mobility).

Through an understanding of evolutionary ecology we can gain a greater appreciation of todays complex biodiversity, it’s fragility when interfered with by humans but at the same time robustness when left alone. The biodiversity we experience in our own lifetimes and from recent historical literature is a snapshot of biodiversity in our present epoch, the Holocene, but different from past eras of billions of years. Future epochs leading onto eras will result in further evolutionary adaptations and extinctions. For me the study of evolutionary ecology helps fully appreciate the science of biodiversity . Today we can identify many examples of co-evolutionary occurrences; beneficial relationships  such as symbiosis  between species of flowering plants and insects. The plant is pollinated for reproduction whilst the insect gains nutritional benefits. This co-evolution began to evolve around 140 million years ago. However wind pollinated grasses evolved about 100 million years later  around 35 million years ago. Wind in my mind is a more efficient means of pollination than relying on insects, perhaps in future eras there will be a demise of present day flowering plants and insects. Similar to fossil evidence of trilobites, ammonites and dinosaurs which are all now extinct. The learning and understanding of evolutionary ecology leads us onto the thoughts of how future life will evolve in the eras come.

What is clear is that humans are having a greater and faster impact on our planet than occurred in the past eras of time. We really have to tread carefully and respectfully to ensure the health of our planets biodiversity. Scientist generally agree on five identifiable major extinction events in the past and there is growing agreement that we are in the midst of a sixth driven by human actions on our planet which could result in our own extinction. Referred to as the Holocene extinction or Anthropocene  extinction this extinction event could be occurring or, as considered by others, simply scaremongering.

The present human population is estimated at over 8 billion, the majority of which will not be aware, understand or care about the implications of collective human actions. Our individual actions may make no real difference, certainly short term but possibly long term they will contribute to the evolution of a planet conscious way of thinking ensuring human survival as well as for the many other life forms we share our planet with. Unseen by the naked eye  bacteria, archaea and viruses still similar in shape and internal organisation and metabolism as exist today having originally evolved around 4 billion year ago. These species of bacteria, archaea have not needed to evolve further successfully occupying their niches. Organisms which evolved over 3.7 billion years ago can still be seen today such as blue- green algae (cyanobacteria) forming green mats on ponds, lichens and mosses among the earliest  plant colonisers of land  can be seen on rocks. Plants such as ferns, cycads and many conifers would have been familiar to dinosaurs but not grasses which evolved about 20 million years later.

Rock surface containing lichens, moss, grass and woody plant species provide clues on how land was first colonised by plants about 543 mya.

Evolution summarised.

The aim of this chapter is to place biodiversity into a summarised geological and biological  evolutionary timescale context.The information is from current consensus of scientific evidence and hypothesis of the probable timings of the main evolutionary events. Compiling this narrative has not been easy because although the main lines of events are evidenced through paleontological and geological studies and separated by often many millions of years, different texts place  boundaries of these main events at slightly different points of time in the past. I have done my best to place the events into the most agreed upon periods of time and am confident I  have placed evolutionary changes in the most  commonly accepted chronological order.  As  future advances are made in scientific analysis and future fossil discoveries some evolutionary theories and timings will no doubt be amended  but hopefully proven not to be too far from accurate from todays interpretations.

It is estimated that the Earth formed around 4.54 Billion Years Ago (BYA), forming from an asteroid belt (a cloud of cold gases and dust) rotating around the sun. These particles of metals and rocks were drawn together by the force of gravity, known as  accretion and this  accumulated mass began to spin on it’s own axis by gravitational pull.  Radioactive heat melted the Earth’s core with heavier metals settling at the core whilst the lighter rocks settled on the surface. Scientists have split the periods of time from the Earths formation into four geological eons each covering millions or billions of years; the Hadean eon, Archean eon, proterozoic eon and the phanerozoic eon.

I would like to point out that the hierarchal timescales are based on geological derived terms and that the following boundaries are historically based on changes in the animal fossil record and that if it had been based on plant records a different hierarchical structure would have resulted. See Phytic paragraph below.

Hadean eon:  Estimated to have lasted around 500 million years from about  4.5 bya to 4 bya. The name derives from Hades, the Greek god of the underworld and the underworld itself. It covers the early formation period when the Earths surface would have been in a very hot molten state, with initially no atmosphere or water. There were no primordial oceans or life.

Gravitational pressure and the radioactive substances held within the accumulated mass  during this eon resulted in hot gases and lava bubbling up from volcanic activity on the hot molten surface contributing to the first atmosphere; a thick mixture of carbon dioxide (CO2), methane (CH4), nitrogen ( N2), ammonia ( NH3) and perhaps water vapour (see Archean eon below). All these elements  contributed to a strong greenhouse effect, raising the planets temperature to an estimated 30°C to 50°C.There is some geological evidence that rock solidification leading to the formation of the first land masses or  supercontinents may have started during the Hadean eon.

Archean eon: This second period lasted about 1.5 billion years from around 4 bya to 2.5 bya.  The name comes from the Greek for ‘beginning’ and signifies the beginning of life on Earth when the initially molten crust solidified.  The Earth’s crust during the Archean was now largely covered by oceans of water much deeper than todays oceans, the atmosphere above was dark and acidic. It is thought that the oceans were formed  by the condensation of atmospheric water vapour, the water was acidic and very warm. It is uncertain how Earth originally came to have water. The favoured theory at present is that certain types of water rich meteorites, as observed in the outer asteroid belt between Mars and Jupiter,  containing water-ice as well as hydrogen, carbon and nitrogen impacted the Earth at this point. When the meteorites impacted the earths atmosphere they would have vaporised. The hydrogen reacting to form water and in turn the early oceans.

Fossil evidence of cellular life of sufficient complexity to leave micro fossil traces demonstrates  life began in these warm primordial oceans around 3.7 bya.  With this reasoning life or self replicating chemical entities that had not formed into organised cells must have pre-dated this and hence the estimate of around 3.7 bya. See The general scientific consensus on how life first evolved above.

The atmosphere at this point lacked free oxygen (less than1%). The first life forms would have been formed deep in the acidic warm oceans where  the sun's deadly UV radiation could not reach. No protective ozone layer would  have existed at this point, These  first life forms similar to, todays bacteria  respired anaerobically some species producing oxygen as a waste bi product. As the oxygen levels in the atmosphere reached 1% *, primitive pre-photosynthetic bacteria able to utilise the sun for energy evolved nearer the surface of the oceans.

These early cells were  prokaryotic (single celled organisms with no nucleus or other organelles) and with crude photosynthetic membranes. These prokaryotic bacterial cells capable of photosynthesis, called cyanobacteria ( relating to their colour), contained a few primitive proteins as they drifted, often in large groups as slime in the oceans, now nearer the surface, absorbing invisible infra red rays from the sun. For nutrition they converted carbon dioxide and hydrogen based organic compounds into energy for growth and reproduction producing sulphurous gases as a waste bi-product. The light absorbing pigments they contained called bacterialchlorophyll were the  predecessors of todays chloroplasts. Over hundreds of millions of years and by around 2.7 bya they had evolved photosynthetic pigments; phycocoblins, carotenoids and chlorophyll allowing them to absorb energy from different wave lengths. The chlorophyll pigments now allowed them  to produce more oxygen as a bi product.

Archaea, share the name with this eon, they are an abundant group of unicellular organisms morphologically similar in size and shape to bacteria and originally grouped with the bacteria. However scientific advances have shown them to have different genes and  metabolic pathways to bacteria. All bacteria and archaea are prokaryotes but archaea are closer to eukaryotes (the next evolutionary  step in unicellular organisms leading to plants and animals) and make up the third branch at the base of the phylogenetic tree or tree of life.

The phylogenetic tree helps biological scientists to  organise their knowledge of biodiversity and visualise  the modern concepts of evolution. This is done through following lines of evolutionary descent rather than ascent  which results in the theory of  a Last Universal Common Ancestor (LUCA). Archaea are found in a wide range of moderate to extreme environments such as extremely hot or acidic habitats. Although much is still to be discovered about the archaea their evolution is important in understanding the origins and diversification of past and present day biodiversity.

*Todays oxygen levels sit  at 21% but over eons of time has fluctuated with estimates exceeding 30% and dropping to 10%.

Proterozoic eon: The Proterozoic lasted about 2 billion years from around 2.5 bya to around 543 million years ago (mya). From the Greek protero meaning earlier and  zoic referring to animal life. The cyanobacteria were now producing oxygen as a bi product in lager quantities causing a greater rise of free oxygen in the atmosphere, effectively poisoning the initially prolific anaerobic bacteria in the predominantly methane atmosphere of the time. This gave rise to the  ozone layer which would provide protection from the harmful solar radiation. This hypotheses of cyanobacteria increasing oxygen in the atmosphere initiating the Proterozoic eon is known as the Great Oxidation Event.

Todays plant chloroplasts are thought to have evolved from an endosymbiotic relationship between the photosynthesising cyanobacterium prokaryotes and non photosynthesising pre- eukaryotes  (enclosing their genetic material within their cell in a membrane called a nucleus) which were also evolving at this point. The very first eukaryotes evolved around 2.7 bya . At this point there is also fossil evidence of the first bacteriophages (viruses infecting bacteria) There is no consensus on whether viruses pre-date both prokaryotes and eukaryotes or evolved from these bacteria.

These photosynthesising eukaryotes in the form of red, brown and green algae which at this point were still marine dwelling organisms are  believed to have been washed up onto the land around 500 mya. Photosynthesising algae are neither plants or animals but classified depending on the  taxonomic classification followed as protists or chromista. Modern day plants are believed to have evolved from these photosynthesising algal chromista.

During the Proterozoic eon  a large supercontinent called Rodinia had formed and the atmosphere continued to become increasingly oxygenated. During this eon there is further  fossil evidence of more forms of eukaryotic life in the form of earliest land fungi and simple multicellular eukaryotes before biodiversity became much more complex in the Phanerozoic. These earliest multicellular eukaryotic red and green algae moving onto the land are thought to have evolved into earliest lichens and bryophytes developing waxy cuticles to resist desiccation.

These first three periods the Hadean, Archean and Proterozoic eons make up the pre-Cambrian period. The Cambrian period which follows is the first of eleven periods in the fourth eon, the Phanerozoic.

Phaenerozoic eon: The last and present period lasting from around  543 mya to present day. In professional scientific literature Ma (for Megaanum) is often used instead of mya (million years ago). I will stick to the latter.

This is the period where prolific and diverse animal, plant and fungal life (biodiversity) is easily visible. The Greek phanero meaning visible and zoic again referring to animal life. Although spanning around 543 million years it is thought that a large number of the ancestors of todays plants and animals evolved in a relatively short period of time, known as the Cambrian Explosion. Estimates of how short this period of time was are continuously being revised. The latest estimate being between 13 to 25 million years starting 543 mya at the beginning of the Cambrian. The Phanerozoic eon is further divided into eleven periods each lasting millions of years.

All four eons above cover extremely long periods of time and geologists have further split them into three sections called ‘eras’ with the  prefixes paleo,(older) meso (middle) and ceno (recent). Therefore in the Phanerozoic eon we get the Palaeozoic era, the Mesozoic era and the Cenozoic era.

Major evolutionary events

The boundaries of the three major eras of the Phanerozoic are all marked by major evolutionary events. The boundary between the Precambrian and the Cambrian period of the Paleozoic era (543mya) is marked by an exponential increase in multicellular animals in the fossil record. The Cambrian explosion as mentioned earlier. The boundary between the Palaeozoic era and the Mesozoic era  (248mya) is marked by 96% of marine species dying out. The boundary between the most recent Mesozoic and Cenozoic  (65mya) is when the dinosaurs and 75% of invertebrates died out. As mentioned earlier geologists split eras based on changes in the animal fossil record and that if it had been based on plant records a different hierarchical structure would have resulted namely the Phytic eras.

Phytic eras

The eras mentioned above  end in ‘zoic’ (relating to animals)  being based on the history of animal life. To add to the complication plant biologists have divided the eras with ‘Phytic’ (relating to plants) endings. Therefore we get Archaeophytic and Proterophytic eras where the earliest plant like life is identified followed between boundaries of Proterophytic and Palaeophytic around 420 mya when the evolution of vascular land plants is seen. Followed by the boundary between the Palaeophytic and Mesophytic around 280 mya with the major expansion of the seed plants and finally the boundary between the Mesophytic and the Cenophytic around 120 mya with the evolution of flowering plants. Apologise for digressing and I will stick with the geological timescales to highlight these events.

The Phanerozoic periods

The first period in the Phanerozoic, the Cambrian, is now believed to have began around 543 million years ago, lasting around 58 million years to 485 mya. This is the period where all the main descendent lines of plants and animals extant today established.  From the fossil record of  this period it can be seen that  during this time many invertebrates  and vertebrates appeared on land from the primordial oceans which at this point were flourishing with life. Prior to the Cambrian period the landmasses would have  been devoid of life because there would have been no organic matter or biologically available minerals for plants to evolve or establish.

The Cambrian and the following Ordovician periods both show lots of tectonic activity. There is lots of movement in the continental land masses through the rising and ebbing ocean levels occurring between interglacial and glacial periods.  Continental shelves supporting shallower water around land edges formed, providing more favourable physical and climatic conditions for aquatic algae to be washed up onto the at this point lifeless land.

Although not a photo,of an algal mat, common duckweed Lemna minor illustrates today how photosynthetic algal mats in shallow, less turbulent aquatic shelves next to barren land would have led to early land colonisation.

By the late Ordovician, around 440mya  there is evidence in the fossil record of early soil formation, organic matter decaying oxidatively through bacterial action and deep burrowing eukaryotic animal life. Evolutionary scientists use observable actions by todays cyanobacteria , algae and eubacteria in breaking down rock material to help understand and explain probable early evolutionary events. The high levels of carbon dioxide in the atmosphere would have been good for photosynthetic organisms forming great mats in the shallow, less turbulent continental shelves. High carbon dioxide levels were good for early soil formation but combined with still high temperatures did  not favour plant establishment outside of an aquatic environment. The early unicellular and multicellular  algae similar to organisms found in todays marine and freshwater environments were as seen from fossil evidence; green algae, red and brown sea weeds, diatoms, dinoflagellates and euglena. The resulting decomposition and build up of dead organic matter would, together with weathering of rocks through acid rainfall and activity of burrowing organisms resulted in the formation of early soils.

Between the Cambrian and Ordovician periods essential requirements for aquatic plants but also animals, fungi, bacteria etc where established so they could make the transition onto land. These requirements being land itself, shallow, less turbulent shore line, soil formation and suitable atmospheric conditions. By the end of the Ordovician period the supercontinent Rodinia  which formed during the Proterozoic eon fragmented  into East and West Gondwana and Laurasia which would over long periods of time lead to the positioning of the continents we are familiar with today.

During the  Ordovician (485-443 mya) period as mentioned  marine life continued to flourish but  made the transition onto the land. Global climates during this period were more variable and in some regions the atmosphere was cooler and moister allowing the first land plants to evolve for terrestrial rather than aquatic habitats.

Primitive plant fossils have been identified around the middle of this period about 470 mya in form of liverworts and hornworts. Liverworts and hornworts are grouped together in a category called bryophytes which include mosses and are believed to have evolved from green algae.The name bryophyte comes from the Greek meaning ‘moss plant’. They have no water or nutrient absorbing roots or structural strength  to hold them upright or vascular system to conduct water and nutrients they have absorbed. Although able to colonise terrestrial habitats they still require moist habitats to  complete their life cycle. They reproduce asexually by water borne spores. There is further evidence of them forming associations with primitive fungi to absorb water and nutrients.Today bryophytes  occupy predominantly damp habitats with the ability to colonise areas rapidly and tolerate high levels of disturbance and exploit rich sources of nutrition. A testament to their evolutionary past and continuing success.

Lichens were also present. A lichen is a mutualistic relationship between two organisms of two of three separate kingdoms;  a fungus which cannot photosynthesise but provides a protective surrounding and probably nutrients together with either a photosynthetic green algae (chromista) or  Photosynthetic cyanobacteria (bacteria). Pre-chloroplast containing prokaryotes are believed to have evolved into green algae which in turn evolved into plants.

What evolutionary development made possible the appearance and resulting biodiversity of plants? It is believed the earliest and simplest Algae cells reproduced asexually by division producing diploid (containing two sets of chromosomes) spores which developed into new algae called  sporophytes, which were the exact copy of the parent. Evolutionary change was made possible by an alternating of generations where the a asexual diploid sporophyte releases its spores (but each spore only contains a single, haploid,set of chromosomes) which grows into a gametophyte which in turn  releases identical male and female gametes which when swimming  together  fuse (sexual reproduction) the resulting sporophyte also termed a zygote starts the cycle again.  Sexual reproduction within kingdoms (plants, animals, fungi etc) allowed adaptation and evolution leading to increased biodiversity with living organisms able to exploit and survive in changing environments.

The early Silurian period (443-419 mya) shows fossil evidence of the first land plants colonising the now muddy fringes of coastal swamps. These plants show water deficient, terrestrial colonising adaptations. Notably early water and nutrient conducting vascular tissue. These plants or tracheophytes had and continued to evolve, able to grow upright and taller to  maximise exposure  to the  sun for photosynthesis with roots to hold them into the soils. Lignin,  a  complex polymer found in vascular and other plant support tissue evolved allowing rigidity and allowed the plants to stand upright. Lignin is found in red algae today supporting evidence of this evolutionary pathway. Fossil evidence of club mosses is also found in the early Silurian. Club mosses are different from true mosses in being vascular rather then non vascular as true mosses are. Club mosses or lycophytes  would have evolved from true mosses or bryophytes. In the animal kingdom ancestors of fish continued to dominate the vertebrates in the oceans and evidence of the the first land invertebrates (animals without a backbone) such as springtails and bristletails are seen.

photo shows brownish non vascular true moss growing in association with darker green vascular club moss or tracheophyte. Today club mosses are small but by the Carboniferous many now extinct species were 40m tall

The  Devonian period (419-358 mya) followed the Silurian and is the period which determined many of the characteristics of todays plants which are not completely dependent on aquatic habitats to complete their life cycle. Now extinct plants included first traces of leafless fern fossils such as Cooksonia (also Rhynia and Zosterphyllum) growing to around 30cm tall with wind dispersed spores carried on the tips of upright stems to transport water and nutrients  and Sporogonites which had early root like structures (rhizoids) for anchorage in the early soils.

Soil is now easily recognisable, built up from the continual oxidative decaying of organic matter. The combined effects of decomposing organisms leaching acids into the rocks together with the action of fungi and evolution of primitive roots to penetrate the substrate keeps contributing to the continual build up of  soils. This period also  shows the evolution of more  primitive wingless invertebrates including  molluscs such as snails and arthropods including  harvestmen spiders, scorpions, centipedes, millipedes  all feeding on decaying organic matter and one another.

They  co evolved with seed plants  such as seed ferns whose spores were enclosed in a desiccation resistant coat.

Early Gymnosperms are also seen in the fossil record. They are plants with their seeds (like todays seed scales found in conifer cones) unprotected by an ovary or fruit. They included tall growing horse tails, conifers, cycads, ginkgo as well as club mosses. Many of them growing much taller than the earliest tracheophytes such as Cooksonia . Because club mosses although growing tall because of a vascular structure, reproduce by spores and rely on an aquatic environment as part of their life cycle so are not classified as gynosperms. Many of them grew to more than 40m tall much taller than todays  common trees like sycamore and lime trees.

Oxygen in the atmosphere was continuing to increase whilst carbon dioxide was decreasing. By the late Devonian fossil records shows an abundance of taller plants with recognisable roots and leaves containing recognisably evolved stomata for respiration. Leaves are believed to have evolved from branching shoots to cope with the increased need for photosynthesis and stomata for the increased need to respire.  Woody lignin containing stems with vascular tissue and sexual organs for reproduction are seen in the fossil record together with evidence of the primitive fungi which are believed to have assisted plants in colonising land by increasing their ability to absorb water and nutrients. This  late Devonian explosion is also the beginning of primitive amphibians and  arthropods co-evolving with  early seed plants.

The Devonian is followed by the Carboniferous period (358-298 mya) and the expansion of the  gymnosperms  with vast swamp forests which today forms unsustainable source of fossil fuels such as coal.

The Permian period. (298-251 mya) shows the proliferation and diversification of the seed plants and conifers, the climate drying and the formation of the single  super continent Pangea. The Permian also shows the first fossil evidence of beetles.

This is followed by the Triassic period (251-201 mya)  known as the Age of Reptiles where dinosaurs evolved as did the evidence for the first flies.

The Jurassic period (201-145 mya) where the dinosaurs continued to flourish and the first evidence of  the ancestor of birds Archaeopteryx. The period when the supercontinent of Pangea splits and now becomes Gondwanaland and Laurasia. Climate becomes wetter leading to conifer jungles.

Around the beginning of the Cretaceous period (145-66 mya)  is where first flowering plants , angiosperms, appeared and diversified rapidly in around 5 million years beginning around 140 mya. Seed ferns or pteridophytes like the dinosaurs become extinct at the end of the Cretaceous period. Seed ferns are considered an thought an intermediate evolutionary stage between todays spore bearing ferns and the  angiosperms (flowering plants).

Discovered in 1994 in a ravine in Wollemia National Park by David Noble, Wollemia nobilis believed to be en extinct gymnosperm which has fossils dating back 90 mya. These trees grew to around 40m tall. This specimen is located in the Botanic Garden of Rome.

The  speed of evolution and diversification of flowering plants compared to previous evolution of rates of earlier the earlier plants; seed ferns and gymnosperms as well as animal species deluded scientist for many years. It is now believed that two things contributed to this . Polyploidy. a plants ability to duplicate large bits of genetic information allowed rapid explosion of diversity. Polyploidy is fatal in animals but not so in plants. Secondly pollen spreading ability.  Angiosperms show structures that attract flying insects for pollination.  Bees make an appearance here co-evolving with flowering plants. Also the first ants make an appearance believed to have evolved from wasps. Insects and flowers are inextricably linked through time in mutualistic relationship.

This brings us to the last two periods the Palaeogene  also known as the Tertiary (65 -2.4  mya) which is marked as mentioned earlier by the end of the Age of Reptiles or dinosaurs and the rise of early mammals.  It is thought a meteorite hitting the Earth wiped out 75% of the species on Earth. By 60 mya there is evidence of owls in the fossil record, by 55mya a great diversity of  birds  are seen and by  52mya bats are seen in the fossil record. Butterfly’s and moths make their first  appearance in the known fossil record about 40 mya.

The Palaeogene also shows  the appearance of Grasses evolved from angiosperms around 35 mya leading to grassy plains which provided food for grazing animals as well as shelter for other evolving mammals. Conifers dominated the colder climates whilst flowering and fruiting angiosperms the tropical climates. By 30mya modern mammals  are evolving and diversifying rapidly.

The Neogene or Quaternary period  (2.4 mya - present) is when moderns mammals evolved, estimates vary but  humans are thought to have evolved less than 2 million years ago with  our  closest extinct species Homo erectus ‘ Upright man’. Our form Homo sapiens ‘ Wise man’ is thought to have evolved somewhere between 550.00 years and 750, 000 years ago. Fossil records show that we started to get smart, making tools about 80,000 years ago.

 

As mentioned at the beginning the above events are by and large in todays consensual chronological order and as new discoveries are made there will be shifts and additions to the events. What is clear is that the two most noticeable kingdoms the plants and animals had periods of rapid expansion of diversity leading to todays flora and fauna.  Fungi and the other kingdoms bacteria etc no doubt had massive expansions of evolutionary biodiversity also. By having a comprehension of how life evolved and evolutionary biodiversity, extinct and extant we can truly appreciate the right to existence that every species on our Earth has and we should respect this evident but under represented fact

There were a number of mass extinction events that wiped out large numbers of species and altered climatic conditions for long periods of time. Isolated surviving pockets of land for example following ice ages allowed the recovery and evolution of biodiversity into the species existing today. Considering the time scales that led to todays biodiversity it can be seen that the rate of biodiversity loss today far exceeds the rate of loss of the past. Is an offhand estimate of 100 times faster  loss a silly estimate considering the millions of years present biodiversity took to evolve? Perhaps it is too low!

The preceding account teaches us the vast time scales our present  biodiversity and complex interactions have  taken to evolve on our planet Earth. Add to this the size of our Earth to the rest of the universe.  The spatial size of the universe is unknown. The term universe includes space and time. The observable universe is thought to be about 90 billion light years across containing billion trillions of plants of varying size. Our sun is 330.000 times larger than earth (1300.000 Earths can fit inside it).  All the matter in the universe including us are made of atoms,  we have a connection  with our universe. We are not just a part of nature we are a part of the universe.