Single celled micro-organisms and their impact on the earth.

The formation of the solar system.

The Sun, along with its attendant planets were formed from a huge cloud of gas and dust that collapsed some 5 000 000 000 years ago due to perturbations within the cloud, possibly caused by a super novae explosion nearby. The sun is made up of mostly hydrogen, helium and traces of other heavier metals, these heavier metals formed the rocky planets one of which we now call the Earth. The lighter gases were blown out to the outer reaches of the solar system to form the gas giants Jupiter, Saturn, Uranus and Neptune. Our earth is a rocky body lying some 150 million kilometres from the sun and is chiefly composed of iron, oxygen, silicon, magnesium and many other elements. The earth is a dynamic system with plate movements; mountain building, ocean forming and atmospheric changes that make our world stand out from the rest of the planets in our solar system.
It seems probable that the Earth is the only body within our solar system that will harbour life of any description; however, there is speculation that Europa may have an ocean of water (under a thick layer of ice), which may support life. However, it must be stressed that all this is hypothetical and will be only resolved if a space craft can succeed in getting to the moon and then burrowing through the ice. Scientists are now working to see if this is feasible, but a mission of this calibre is unlikely to happen soon
The search for life on Mars is now becoming ever more unlikely to bring fruition, with scientists now discounting the likely hood that there are really Martian microbes embedded in the ALH84001 1.9 Kg meteorite from mars. The so-called microbes are extremely small and it is doubted whether even the DNA molecule could fit inside this cell. This however, does not mean that there has never been life on Mars at some period, it just seems very unlikely and the only way forward is to send more unmanned probes into space until we succeed in finding something, whether on Mars or else where.
Recently, astronomers say that they have detected other planetary systems orbiting other stars within the Milky Way galaxy, it must be stressed that these planets are huge and are most likely composed of gas similar to Jupiter and Saturn. Whether there are any rocky planets' orbiting these systems remains to be determined. It should also be remembered that if there are planets orbiting a suitable star this still may not be a haven for life, many factors go into the making of a planet appropriate for life. It is likely that scientists will develop methods for detecting the presence of life by looking at the atmosphere of these planets with new orbiting telescopes. The big question that scientists are trying to answer is how life gained a foothold on the Earth. Scientists know for certain that the Earth of 5 billion years ago was very different from the world that we inhabit today.

The planet Earth viewed from space. The large continent of Africa can be seen to the bottom right. Most of the Earths surface is covered in water. Liquid water, an atmosphere and the right distance from the sun all helped to kick start life within a few hundreds of millions of years after it's formation. This photograph is from the Encarta encyclopaedia.

When the Earth first formed it was under an incredible bombardment from huge meteorites and comets and the surface must have been completely molten. To get some idea of what took place go out side and look at the moon when it is showing it's first quarter with a pair of binoculars; and see some of the huge impact craters that occurred billions of years ago.
When Mariner 10 visited Mercury way back in 1974 scientist were surprised at the amount of craters that were seen on this small world. Venus and Mars have their share of large craters giving more weight to the idea of planetary accretion. The constant weathering, volcanism and plate movement of our own planet have all but removed the traces of this ancient bombardment.
It is probable that the original atmosphere has been completely replaced very early on in the Earth's history by the intense solar wind and bombardment by large meteors and other debris from the solar system. The Earths later atmosphere was the result of out gassing by the many volcanoes and fissures that were erupting at this period. The gasses that were present would have been extremely toxic to modern life forms; the atmosphere would probably have consisted of mostly Carbon Dioxide with some Nitrogen, Carbon monoxide, methane, ammonia, hydrogen cyanide and water vapour. It is also probable that the atmosphere was also much denser than it is today. The truth about the earth's early atmosphere will probably never be known for certainty.
With the Earth looking like a giant fireball most of the heavier elements, such as iron, would sink towards the centre of the Earth; while the lighter elements would be pushed upwards to the surface to form a crust. How long the Earth was in this molten state remains unclear it must have been for many millions of years. The latest evidence for life on Earth places single celled organisms back to 3.8 billion years, so certain areas of the Earth must have been cooler or at around a 100 C at this time. The oldest rocks found on the Earth are found in Isua in Greenland and are reported to be 3750 million years old, they consist of sedimentary and volcanic rock.

Scientists were for many years perplexed has to how we acquired such a large moon, perhaps it formed along side the Earth or was even captured at some later date. Some scientists maintained that the moon was ripped from the earth early on by the excessive spin of the earth on its axis. The Pacific Ocean basin was claimed to be the site where this event took place but the theory of plate tectonics and dating of the ocean bed meant that this idea was also unworkable and this idea was also dropped. With the magnificent engineering feat of putting men on the moon and returning samples of moon rock, it quickly became apparent that none of these scenarios would fit the bill and were pushed into the background.
The latest theory seems to answer some of the problems that were associated with the early models, but this latest theory may not be the final story. The uncertainties about the formation and beginnings of the solar system and life are what make it so exciting, just when scientists think that they have solved part of the story some new piece of the jigsaw is found and the model has to be modified. I believe that the main part of the story is correct and that the scientists have done an incredible piece of detective work to get us this far in our understanding of the solar system.

The Earth has a large moon in comparison to other planets within our solar system, (except for Pluto and its moon Charon) and it is now thought that our moon was created by the impact of a Mars sized object with the Earth very early on in the formation of the solar system. The rocks brought back from the moon by the Apollo astronauts seem to consist of the same material as that of the Earths crust.
If the latest theory is true then the impact must have been titanic to say the least, with huge amounts of material being blasted into space, which would then join together to form the moon, with the rest either falling back onto the Earth or drifting of into deep space. This collision may also explain why the Earth is tilted on its axis at 23.5 degrees perpendicular to its orbital plane. There are problems with this theory in that it would require the earth to have melted through out, but observations do not entirely fit with this scenario.
What impact would this fortuitous collision have had for any future development of life on earth? The earths axis precesses once every 26 000 years due to the moons (sun) gravitational tug. This gravitational pull of the moon may also have helped to stabilise the tilt of the Earth preventing it from wobbling too much and becoming chaotic. The tilt now gives us our seasons and helps to vary the amount of heat and light that the Earth receives. With the moon in close proximity to the earth the tides must have been enormous and would have prevented any life from gaining a foothold near the shorelines; also the effect on the ground would have been enormous. The moon picked up the lost angular momentum from the Earth's slowing rotation and gradually started to drift further away, allowing for more smaller tides where life could gain a foothold at the sea- land interface. Whole communities have since grown around the ebb and flow of the tides.

This photograph was taken by David Greensmith in 1996 and shows the famous meteor crater in Arizona. The crater is 1200 meters across with a depth of 180 meters. The size of the lump of iron is thought to be about 50 meters across and was travelling about 18km/s. The kinetic energy released would have been incredible, something in the region of a large hydrogen bomb exploding.

What effect this impact in Arizona would have had on the global scene is not sure but for the local flora & fauna it would have been devastating to say the least. Much larger craters have been revealed on the Earths surface by orbiting spacecraft. The Manicougan crater in Quebec is thought to be at least 200 million years old and Gosses Bluff, which is in Australia, is also a large impact crater. The most famous of all, is the asteroid that crashed into the Yucatan peninsula some 65 000 000 years ago which possibly helped the demise of the dinosaurs at a much faster rate than would have normally happened.
There is much evidence for a large amount of volcanic action around this period with the Deccan traps on the Indian sub continent spewing out huge amounts of poisonous gasses. It must also be remembered that many species of dinosaur were already on their way out 65 000 000 years ago. It is more probable that climatic changes due to tectonic and volcanic eruptions changed the climate to such an extent that many life forms simply could not cope and consequently perished.
There have been other mass extinctions on the Earth and whether asteroids or comets have caused these is open to debate. For instance the Permian-Triassic boundary shows a huge decrease in the number of species due to large eruptions of flood basalt in the Siberia region of the planet. It is thought that perhaps 90% of life disappeared at this boundary. It seems that the extinction of species is part of the normal process of life here on Earth. What may be a disaster for many species opens up new areas for animal life that would not normally gain a foothold in that present climate. Much remains to be discovered about why species disappear. An intriguing question is to how many different life forms have at one time or another been on this Earth, it must number in the hundreds of millions.

This photograph was taken in 1992 from my back garden here in the suburbs of London. The light pollution does not make that much difference when a bright image such as the moon is photographed. The instrument that I used was a 4" refractor with an Olympus OM-2 mounted on the eyepiece end. Note the huge amount of cratering that this small world received many billions of years ago. The Earth must have received the same treatment as the moon but weathering and plate movements have helped to hide the scars. The film was T-max 100 and was developed in T-max developer.

Eventually the Earth cooled and water vapour condensed into liquid to form the oceans that we see today. If it were possible to fly over the Earth at that period it would be unrecognisable, and extremely inhospitable to any modern day life forms. No one knows for sure how long it took the Earth to cool sufficiently for liquid water to form the oceans but it must have been many hundreds of millions of years. The bombardment of the planet stopped about 3.8 billion years ago but it is obvious that other large bodies would have impacted with the earth for many millions of years after the main bombardment had finished. The continental masses were not as large as their modern day equivalents and probably were split into many smaller land masses. No one knows whether the continental pates were moving any faster or slower than the plates of today. But what is certain is that there was a huge amount of volcanic activity and large amounts of magma along with various gases being thrown up from within the earth. Along with new land being added the atmosphere and also the mineral content of the oceans must already have begun to take shape.
Life may have got started and then been extinguished on more than one occasion; but this is pure speculation because of the lack of any fossilised evidence from this period. Any rocks would have been squeezed, crushed and melted many times over at this period of the earth's history.
But it was within this scenario that the first indications of life began to stir. What these first replicators were is again unknown and it is certain that they would have been very different from anything that we find today. Modern cells are very complex chemical factories with millions of reactions taking place every second.

This photograph shows a freshwater spirochete magnified about X700. The bacterium was photographed with a X40 DIC objective.

What scientists are trying to figure out is how inorganic chemicals bridged the gap to become organic. Which came first, DNA, RNA or proteins? What is certain is that a molecule gained the advantage over all the rest and began the fairly complex task of reproducing its self, and eventually within a comparatively simple membrane bounded cell. The molecule on its own does not constitute life this would come only once the membrane had formed and cells could replicate. The key to success is being able to replicate over and over again but also being able to take advantage of any mutations that take place. Any slight advantage over the next molecule means that it may get to replicate faster and also get a bigger share of the nutrients that are on offer. The successful proto cells would proliferate and eventually begin to dominate the environment. These molecules must have had primitive catalysts that speeded up the reactions, but these would certainly not be the proteins that are found today. Being able to keep pace with the earth and its geology meant that any new niches that became available to the molecule would be exploited quickly. Natural selection by evolution happened very early in the dawn of life.

This photograph was taken with phase contrast, and from this tiny sample millions of bacteria could be seen.

Bacteria have a cell wall made up from various polysaccharides which also include peptidoglycan; this cell wall prevents the cell from bursting open when water is taken up. The cell wall is also important in maintaining the shape of the cell. There are no membrane bound organelles within the bacterial cell. The DNA of the bacteria is in the form of multi loops and does not contain any histones which enable the DNA to fold in on its self. There are also plasmids within the cell body that also contain smaller amounts of DNA. Back in the 1950s scientists discovered that there were two different types of bacteria that mated. They called these different mating types (F) + and (F) - where F means fertility. The (F) + bacterium was able to pass DNA to a (F) - bacterium by what is called a pilus; this appendage allows the 20 genes that are contained on the loop to be transferred to the (F) - bacterium. The transfer can only take place if the two cell bodies are in contact with each other. Scientists discovered that this transfer of genetic material is useful in being able to confer immunity against certain types of anti-biotics. Unlike eukaryotic cells the DNA is not contained inside a membrane.
The membranes of modern eukaryotic cells are made up of two phospholipid membranes that enable the chemistry of the cell to be concentrated and controlled. Situated within the fluid membrane are various carrier proteins and cholesterol molecules. The membrane acts like a gateway only allowing certain molecules in and out of the cell body. Some of the proteins have chains of carbohydrates attached to them which act as identification and binding sites, these are called glycoproteins. The membrane is roughly about 7nm across. The organelles that are found within the cell body are also membrane bound these include the Golgi apparatus, nucleus and mitochondria.

This photograph shows a modern eukaryotic cell in the process of dividing. The Euglena will split down the middle to form two new cells.

Scientists are also debating where this first life could have arisen. Darwin thought some warm little pond would have been the ideal spot while other scientists thought the oceans or seas of long ago might have been a better choice. The most recently favoured spot is the deep sea black smokers with their abundance of thermal energy and chemistry spewing out into the cold dark recesses of the ocean. Did life originate here or did microbes drift down from the surface to these places over the millions of years and eventually claim this territory for their own. Judging from what geologists and astronomers have discovered about the early earth and sun, the surface areas of planet earth would not have been a good place to hang around, so maybe life did get started in a "safe" part of the earth away from the deadly rays of the newly formed star.
There must have been an abundance of chemicals and energy available to start the ball rolling, and once the first replicators arrived, natural selection would begin to wheedle those out that were unable to adapt to the rapidly changing conditions. The abundance of chemicals in the seas and lakes would not last for long and maybe this is when predators first evolved. Those primitive cells that could protect themselves from predation or become efficient predators themselves would proliferate. Single celled organisms that we call prokaryotes (cells that lack a membrane bound nucleus) held reign on the Earth for over 2 billion years gradually changing the atmosphere and making it ready for the next stage in the evolution of life. Traces of these primitive cells (stromatolites) have been found in rocks from the Precambrian period dating back over 3.5 billion years. There is some dispute has to whether these really are fossils or artifacts created by geochemical means. Stromatolites are the fossilised remains of Cyanobacteria and other microbes that lived in sheet like masses. Some of the earliest records of these fossilised remains date back some 2.7 billion years and can be found in Ontario Canada. Another site is at sharks bay in Australia where Stromatolites are still growing today after their first appearance 3.5 billion years ago. The water that they grow in is extremely saline and therefore there are very few predators that can graze upon them.

.

One thing that stands out about these single celled organisms is that they did not change appreciably in form or function for over a billion years. Evolution carried on at an extremely slow pace until the arrival of cells that could swap genetic material with each other.
In the 1970's vents at the bottom of the oceans were discovered. These vents are the result of volcanic activity and are due to the movement or spreading of the oceanic crust. Water seeps down through the many cracks in the seabed floor and is then heated up by the red-hot magma. This super heated water becomes impregnated with various chemicals such as hydrogen sulphide while on its journey back up to the sea floor. Bacteria have been quick to colonise these areas and have formed rich colonies that reduce the sulphur to make CO2. It is possible that the first life forms on Earth may have developed in areas that are similar to the hydrothermal vents. Chemo synthesis is the prime source of energy and many larger creatures have learnt to exploit the sulphur oxidising microbes that live here. What the first life forms were like is again open to discussion but they must have been even simpler than the bacteria that we find today and were also equipped to live in what we would term extreme conditions.
Prokaryotes reproduce themselves by a method called binary fission where the parent cell divides into two identical daughter cells, this along with their speed of reproduction, size and their ability to change their metabolism has enabled them to be successful for so long. Bacteria can also produce spores that enable them to resist extreme conditions where most other larger organism would fail.

This photograph was taken with a X40 phase contrast objective and shows bacteria in the act of spore formation. Endospores form in certain gram-positive bacteria by becoming dehydrated and forming a thick wall around the newly replicated chromosome. Many spores can remain viable for centuries and even resist fire, chemical, radiation and freezing temperatures. The spores form at the tip and anywhere up to the middle of the cell depending on the species. The old bacterial cell wall ruptures and releases the spore into the environment. These spores are not reproductive cells. When conditions are right the spores are re-hydrated with the help of enzymes and metabolic activity once again commences. Photograph Steve Durr.1999.

Some 2 billion years ago Cyanobacteria and photosynthetic bacteria began to change the amount of oxygen in the atmosphere appreciably through the action of photosynthesis; this can be attested to by looking at the banded iron formations that are found scattered around various localities on the Earth. Banded iron deposits were laid down some 2 billion years ago and are between 50-600 metres in thickness. It is thought by scientists that these banded iron deposits could only have been laid down with the help of photosynthetic bacteria that would have thrived in the warm shallow volcanic vents. Eventually the amount of oxidation would cease and the free oxygen would begin to accumulate in the atmosphere, once this happened the BIFS stopped forming.
To the first microbes that lived, the presence of Oxygen in the atmosphere would be extremely poisonous and would have destroyed many of the life forms that had held sway on the Earth for millions of years. To those that could utilise this very reactive gas a new more efficient energy source would be available with more ATP becoming obtainable for work within the cell.
The ozone layer was formed around 2 billion years ago by the process of sunlight acting upon the oxygen to convert it into O3, which helps prevent harmful short wave ultra violet light from reaching the surface of the Earth, thus enabling larger life forms to evolve that can live on the land. Many of the first organisms would have had to live in the water, which would help protect them from harmful UV.

This photograph of the sun was taken with my 102mm Vixen refractor with a NGC Max solar filter. The sun is the ultimate power source for all life on this planet giving us warmth and energy in copious amounts. A large group of sunspots can be seen in the top right of the photograph. The sun is a fusion reactor converting hydrogen into helium giving off huge amounts of energy in the process. The suns energy was down by 30% some 3-4 billion years ago. It is thought that gases such as methane and carbon dioxide from volcanic out gassing prevented the earth from going into a deep permanent freeze during this period.

The sun is a fusion reactor and sustains all life on Earth in one way or another .Jim Doyle a physicist at Napier University Edinburgh has written an account of how the sun produces this prodigious amount of energy, and how scientists have, over the years managed to work out how the sun actually does what it does. Give Jim's page a visit and found out for your self about this incredible ball of gas we call the sun. There are also other pages on relativity that you will also find very interesting.http://www.btinternet.com/~j.doyle/SR/Emc2/Fusion.htm
Photosynthesis is a process where sunlight, water and carbon dioxide are turned into the carbohydrates that most other animals, whether directly or indirectly need to survive, and is without doubt the most important process that is carried out by any living entity on this planet. The phytoplankton living in the sea are responsible for the millions of tons of carbon that is fixed into organic compounds each year and pump out a huge amount of oxygen that we need in order to respire. This remarkable process takes place within the cell organelle called the chloroplast, which is composed of a series of flat discs called lamellae. The lamellae are stacked one on top of the other like a stack of plates and they orientate themselves in order to collect the correct amount of sunlight. The conversion of light energy, CO2 and water into ATP, glucose and other cell components is carried out in a series of chemical reactions within the chloroplast. The chlorophyll molecule consists of carbon and hydrogen with a porphyrin ring that surrounds a lone atom of magnesium. The end product can be shown as a simple chemical equation.
6CO2 + 6H20 + Sunlight = (C6- H12- O6) + 6O2.
Photosynthesis is split up into two parts. The light reaction as its name suggests needs the energy from light to drive the chemical reactions. The second part of photosynthesis can operate without the direct input of light energy and is called the dark reaction.

Light reaction- The start of the reaction begins by the absorption of light by the pigment called chlorophyll, electrons are given so much energy that they can leave the chlorophyll molecule. The electrons are then passed along an electron transport chain to form NADPH and ATP. The water molecule that is split into H+02 replaces the lost electrons from the chlorophyll molecule. The oxygen is released into the atmosphere as a waste gas. The hydrogen is combined with CO2, which goes on to form glucose, starch, cellulose and various proteins. Light reaction =ATP+NADPH+O2. Both NADPH and ATP are then eventually released into the stroma, which is where the enzymes for carbon fixation are to be found.

Dark reaction- this part of the reaction takes place within the stroma, which is the space between the thylakoids. The ATP&NADPH drive the Calvin cycle, which uses the CO2 and a five-carbon sugar to build the carbohydrates, which are then stored or converted into the various cellular components. The Calvin cycle is carried out in minute steps and an enzyme regulates each step. This is out of necessity a very simplified account of what actually takes place within the plant cell.

This is a photograph of a cyanobacterium or blue green algae, as they were once known. This species is called Merismopedia elegans and forms a mat that is one cell in thickness. It is microbes similar to this that helped to transform the planets atmosphere from anoxygenic to oxygenic. Photograph Steve Durr 1999.

The next leap in the evolution of life was the Eukaryotic cells with their membrane bounded organelles. These cells had within them mitochondria ( and very important to modern life forms ) the chloroplast, it is thought by some scientists that these organelles were captured bacteria that have learned to live in symbiotic relationship with the host cell. Another great advancement that was brought about by the Eukaryotic cell was the introduction of sexual reproduction, enabling the cells to acquire variations through genetic exchange at a much faster rate. This shuffling of genes enabled organisms to radiate out into the many niches that were available and over the next 700 000 000 years many diverse and wonderful creatures emerged to inhabit almost every part of the dry land, air and oceans.

Introduction to photomicrography.