Saturday, March 17, 2018

Paper: Evaluating The Fossil Record Of Earliest Life

Understanding ancient life: how Martin Brasier changed the way we think about the fossil record - JONATHAN B. ANTCLIFFE, ALEXANDER G. LIU, LATHA R. MENON, DUNCAN MCILROY, NICOLA MCLOUGHLIN and DAVID WACEY

I really enjoyed reading this paper which came out in a special publication issue of the Geological Society, London, in 2017. It is a tribute to the work of Martin Brasier who made significant contributions to our understanding of early life and early animal evolution. In particular, Dr. Brasier argued for a more rigorous approach to analyzing fossils, or claimed fossils, of very early life. He developed detailed criteria for describing and interpreting enigmatic structures as either abiogenic or biogenic, and promoted the use of cutting edge imaging technology to better visualize 'fossil' structures in two and three dimensions.

An excerpt:

Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient fossils. Structures reported from the Apex chert (3.46 Ga) that were interpreted to occur in sedimentary rocks and to be biological in origin (Schopf & Packer 1987; Schopf 1992, 1993) were, for a decade or more, considered compelling candidates for the earliest fossils. Martin Brasier’s most important contribution to this debate was to characterize those structures in great detail and to develop a framework within which claims of the ‘oldest’ or ‘earliest’ life should be couched. In his lectures on this subject, Martin referred to the competitive tendency among palaeontologists working on early life as the MOFAOTYOF principle: My Oldest Fossils Are Older Than Your Oldest Fossils.

In particular, Brasier et al. (2002) made it clear that the burden of proof must fall on those making the claim of ancient life, not those refuting it: Ancient filamentous structures should not be accepted as being of biological origin until all possibilities of their non-biological origin have been exhausted. In particular, it is important to note that complex ‘septate’ carbonaceous structures can result from experimental hydrothermal processes. (Brasier et al. 2002, p. 80) In other words, we should assume that ancient structures resembling fossils, such as those in the Apex chert, are abiological until it can be shown beyond reasonable doubt that they are not, rather than the other way around. Brasier (2015) articulated this concept clearly:

This . . . allows palaeobiologists to set up a hypothesis which will prevail until proved false . . . Any newsworthy, and culturally challenging, interpretation must therefore be tested against a less exciting interpretation. This ‘null hypothesis’ is usually regarded as the ‘most boring explanation’. It is boring precisely because it is thought to have a higher probability of being correct. Brasier (2015, p. 9).

This could be thought of as Brasier’s razor: ‘the most boring answer is probably the correct one’.

This critical approach applies to the problem and controversies surrounding  the fossil record of the earliest animals too. A reassessment led Dr. Brasier  to retract his previous claim about the earliest sponge spicules from the Late Ediacaran ( ~ 560 million to 541 million years ago) age deposits of Mongolia.

Finally, his work on accurately characterizing the scratches, pits, holes, undulations, blobs and globules on and within sedimentary deposits has enormous implications for the search for potential fossils on other planets.

Dr. Martin Brasier died in a car accident in 2014. 

Open Access.

No comments:

Post a Comment