Chapter Eight

First life - Prokaryotes, archaea & bacteria 

8.1 And here is where biology takes over to describe the life in the lake’s water.

8.2 The intimate story of life in the lake begins a very long time ago. Although the lake was formed from glaciers which melted by the end of the last ice age some 18,000 years ago, the lake’s microbial life can trace its origins to the first life forms to arise in the oceans some 3.8 billion years ago, or perhaps even 4.1 billion years ago based on a very recent paper by Elizabeth Bell et al, from University of California.

8.3 As far as we know the first life form were the Prokyarota (meaning single cell with no nucleus). But something very interesting must have been going on in those pre-life oceans during the several hundred million years of their existence, because when the first, simplest, most primitive form of life appeared, the single prokaryotic cell, (pictured above) it was already a fantastically complex creation. In similar fashion, our far distant descendants may one day declare  the first human artifact to be Apollo 13.

8.4 That pre-life ocean may well have contained at the outset a wealth of organic components, complex molecules, and organic compounds, which themselves evolved elsewhere in space, maybe billions of years earlier, and arrived already dissolved in the oceans. A particularly large and rich region for detecting interstellar molecules is Sagittarius B2 (Sgr B2). This giant molecular cloud lies near the center of the Milky Way galaxy and is a frequent target for new searches. Some 50 or so complex molecules, including Benzine, Acetone, and Ethanol, useful building blocks of life, have been detected there.

8.5But it was a steep evolutional step from this initial ocean solution, to the "RNA World" – a phrase first used by Nobel laureate Walter Gilbert in 1986 – to describe the pre-life oceans of the Hadean eon. RNA is the molecule which brings about the ability to replicate and grow, but predates life itself.

8.6 Ribonucleic acid, along with proteins and carbohydrates, constitute the three major macromolecules essential for all known forms of life. Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. Some RNA molecules play an active role within cells by catalyzing biological reactions. One of these active processes is protein synthesis, a universal function wherein RNA molecules direct the assembly of proteins on ribosomes

8.7 But where did RNA come from? As Nick Allen says, ‘The idea that replicators life RNA were the first figments of life, predating any thermodynamic driving force, is, in mike Russel’s words, “like removing the engine from an automobile and expecting the regulating computer to do the driving”. 

8.8 Instead Nick Allen describes the primordial role played by thermodynamics.  “Thermodynamics is one of those words best avoided in a book with any pretence to be popular, but it’s more engaging if seen for what it is: the science of desire.  The existence of atoms and molecules is dominated by ‘attractions’,  ‘repulsions’ ‘wants’ and ‘discharges’, to the point that it becomes virtually impossible to write about chemistry without giving in to some sort of randy anthropomorphism.”

8.9   And this leads to speculation that the kind of assembly of organic components including RNA may have first taken place in and around hot smoking chimneys at vents well beneath the ocean surface such as at the Galapagos Rift. “This bizarre and isolated world seemed to be a vision of Hell.  Surely only the disturbed mind of Hieronymus Bosch could have imagined the giant tube worms, lacking either a mouth or an anus, and the eyeless shrimp, swarming in countless multitudes on the ledges beneath the chimneys, grotesque as a plague of locusts. Life in the smokers doesn't just endure these infernal conditions, it can’t live without them, it thrives on them. 

8.10 But how?  The answer lies in disequilibrium. As seawater percolates down to the magma beneath the black smokers, it is superheated and charged with minerals and gases, ost notable hydrogen sulphide.  Sulpher bacteria can extract hydrogen from this mix and attach it to carbon dioxide to form organic matter.

8.11 New studies continue to push the boundaries of this debate on the origin of life almost every month, as well as to what happened next.  For many years it was thought that the first, and simplest, form of life, the prokaryotes (single cell, no nucleus) were all bacteria.

8.12  But as recently as 1977 a whole new domain of life was discovered, microbes with the ability to live in extreme environments – some of which are referred to as extremophyles. They were named Archaea after the Archean eon whose extreme conditions persisted for the next 1.5 billion years on earth after the Hadean.  When these microscopic organisms were first discovered, they were considered bacteria. It became apparent however, that they were not when their ribosomal RNA was sequenced.

8.13  Archaea may be the oldest form of life on Earth, because they require neither sunlight for photosynthesis as do plants, nor oxygen as to animals. Archaea absorb CO2, N2, or H2S and give off methane gas as a waste product the same way humans breathe in oxygen and breathe out carbon dioxide.  This discovery gave further support to the idea that life originated on earth, not on the placid surface of the ocean, a gentle primordial soup warmed by sunshine, but in the hellish conditions of smoking vents beneath the ocean surface such as described above.

8.14  The  evolution of the next great domain of life, the bacteria, relatively well established.  The first single bacterial cell  began a long path of evolution starting with branches to  Aquiflex, Thermotoga, Bacteroid Cytophaga, and soon to  Cyanobacteria the main protagonist of our story.  Some 4 billion years of evolution have led to the present domain of bacteria, arguably the greatest of the three kingdoms of life. (see recent tree of life Hug et al.)

8.15  This is where one of the many different types of bacteria rises to the forefront with a brilliant invention, an invention which was to be the foundation of rapid growth, plant life, animal life and all complex terrestrial life we know today not least ourselves. Cyanobacteria come up with the idea of photosynthesis.  A brilliant scheme to take transparent water, add to it invisible air, and weightless sunlight and get all the forms of plant life we know today.

8.16  Soon Cyanobacteria with their unique evolutionary competitive advantage went forth and multiplied to the extent that they completely changed the world.  Not only did they grow in vast numbers, the by product of all their photosynthetic industry was free oxygen.  It is estimated that Cyanobacteria were responsible for raising the oxygen content of the earth’s atmosphere from 3% to its current 16% and thereby creating the conditions in which complex terrestrial life forms could evolve.

Continue Reading   Chapter Nine