Is Terrestrial Life of Extraterrestrial Origin?

A few weeks ago a paper titled Life Before Earth was posted on the arXiv preprint repository. It came to my attention by way of this MIT Technology Review article and this blog post. The paper, using a rather simple extrapolation, argues that the apparent rate at which the complexity of terrestrial life increases suggests that its birth occurred approximately 9.7 billion years ago. Earth, in contrast, is around 4.5 billion years old. If their extrapolation is to be believed, then this discrepancy can only be resolved if terrestrial life is in fact of extraterrestrial origin. I will briefly summarize their argument, but I will not attempt to justify its validity. The original paper can be read here and is fairly accessible. The paper’s conclusions are consistent with a fact that has always puzzled me; the surprising complexity and maturity of what is known as the Last Universal Common Ancestor. It is this topic that I wish to focus on in this post.

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Emergent Modularity

Last week I attended a talk at MIT by Michael Deem, a professor at Rice University who has done some very interesting work on the emergence of modularity in evolution. This is a topic that I have long thought about, as it seems that modularity is intrinsic to many biological phenomena, and it also seems that modular systems would by construction have certain internal structure that can be exploited in computational modeling. My thinking on the topic has been crude and qualitative, and so it was with some delight that I discovered Michael’s work in this area, as his group has placed this problem on very firm quantitative footing. The talk was thought provoking, and left me with genuinely new insights, something that happens with only a small, small fraction of the talks I attend.

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