Searching for life in 3-billion-year-old fossils: Will we know it when we see it?

fossil

Geologists examining fossils in rocks help us to gain purchase on the conundrum of what constitutes life by identifying its remains. For relatively recent fossils – think dinosaurs – the answer is straightforward. Though extinct, their bodies look much like extant organisms: bilaterally symmetrical, bearing notable features such as skeletons, teeth and tails. But life was altogether different before the Cambrian Explosion.

What, then, of the remains of first life-forms, those that lived and died on an Earth almost entirely unlike our own, at a time before continents accreted, when sulphurous seas stretched across a young planet?

How would one recognise fossils that are 2.5 to 3.9 billion years old?

To answer the question with which I opened – what do the remains of life look like? –they look a lot like all sorts of other things. Or, to turn the question on its head, lots of old things look a lot like what we expect old life to look like, whether in its form, complexity or simplicity. If once ‘beauty’ and ‘complexity’ were markers of life, and later geobiologists sought early life in its starkest simplicity, now neither is sufficient. Nothing visibly distinguishes the vital from the non-vital when looking for ancient life. Simply put, the search for ancient life is no longer a search for ancient lifeforms.

Read full, original post: The shape of life

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