Abiogenisis, the question of the origin of life
When did life begin on earth?
How did it begin?
What was it doing?
What impact did it have on the earth?
What kinds of evidence do we have for its existence? Is it conclusive?
Life began on earth sometime between around 4.4 billion years ago, when first water vapour liquefied, and 2.7 billion years ago, when measurements of the ratio of the isotopes of carbon (C12 to C13), iron and sulphur in rocks begins to indicate a biogenic origin.
The earth's crust undergoes a constant process of metamorphosis through the forces of plate tectonics. The crust material is constantly being re-cycled, reduced to sediments, heated (even super-heated), compressed, subjected to the passage of hot fluids ... This makes it very difficult to collect direct evidence about conditions in the distant past; the rocks have simply been deformed too much. How then can we determine when life began on earth?
Researchers into the very distant past must rely on indirect evidence. Unfortunately, no one line of evidence is conclusive; researchers must measure many different indicators to generate persuasive results. The oldest rocks found today are part of sediments and lava flows that indicate that the processes of re-cycling already had a long history.
Nicola Mcloughlin a post-doc researcher under Harald Furness in the Early Earth and Biosignatures Research Group at CGB, summarised the currently accepted beliefs about significant dates in the earth's abiogenisis (or question of the origin of life) at a recent informal seminar.
She underlined the difficulties inherent in this research area with a contemporary example. Within the field of Abiogensis there is currently extensive debate about the controversial aging of an outcrop of rock on a tiny island, Akilia, west of Greenland. Analysis of zircon crystals deep with the now exposed ancient rock layers gave a carbon isotope signal with low levels of C13, normally considered indicative of life having been present. Mcloughlin, however, presented a convincing case for there being insufficient information to make a conclusive case. She explained how the crystals themselves have concentric layers of various ages, to say nothing of the layers of rock in the outcrop itself, which are particularly distorted and convoluted, and there are other possible explanations for the low C13 levels. New techniques including an unobtrusive vibrational technique are being applied to the material in the hopes of learning more information about and maybe resolving this controversial case.