Life Before Earth?

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A few days ago, biologists Alexei Sharov and Richard Gordon published a paper that sent shock waves throughout the academic community. In their paper titled Life Before Earth they propose that life originated before the formation of our planet. But just in case that wasn’t radical enough, they further state that:

adjustments for potential hyperexponential effects would push the projected origin of life even further back in time, close to the origin of our galaxy and the universe itself.

In my last post I discussed the transition from non-life to life. However, no where in that article did I discuss the timing of that transition. The dominant view at present is that life originated ~3.5 billion years ago. This estimation comes from direct and indirect evidence of prokaryotic (single-cell organism) activity in Western Australia and South Africa. Although it is hard to prove empirically, most biologists are confident that life on Earth did not exist before this period. This is because between 4.6-4.0 billion years ago Earth can best be described as a chaotic hellscape of magma oceans and planetesimal collisions (i.e., not the best place for RNA replication).

But this latest paper by Sharov and Gordon claims life existed before earth (before even the formation of our galaxy). To be precise they calculate the time of origin for life to be 9.7 ± 2.5 billion years ago. For context our galaxy is ~8 billion years old, and our solar system and planet is 4.6 billion years old.

How could this be?

The authors propose that biologists have neglected to acknowledge the “cosmic time scale” of life. In their paper they posit that in terms of genetic complexity life has grown exponentially (they measure genetic complexity by the number of non-redundant functional nucleotides). Prokaryotes, eukaryotes, worms, fish, and mammals were included in the authors study sample and genetic complexity was plotted on a logarithmic scale (Figure 1). With these data they found that genome complexity doubled every 376 million years. They conclude that if genome complexity doubles at this rate prokaryotic complexity could not have been achieved by 3.5 billion years ago. Both Sharov and Gordon blame biologists of presuming a rapid primordial evolution in order to fit the time scales required by our planet’s age.

log.png Figure 1

Within this new proposed framework the authors suggest that this exponential doubling time is an inherent evolutionary process accelerating quickly with new, more efficient forms of information storage than genomes (e.g., highly complex brains, language, books, computers, internet). Now I am definitely someone that believes exponential growth is an inherent property of evolutionary processes. I am also someone that thinks evolutionary processes generally tend towards greater and greater levels of system complexity (even though recent research has demonstrated that this is not always the case). However, more than doubling the time of the origin of life proposes a radical re-imagining of life and our universe. Such a proposition demands tremendous evidence. I commend Sharov and Gordon for proposing a bold idea and approaching the evolution of life from a novel perspective, but they did not provide us with tremendous evidence.

Biologist PZ Meyers was first to point out that they cherry picked their data. They did not include many organisms that would have completely thrown off their logarithmic scale. Furthermore, even if the logarithmic scale with all organisms plotted remained unchanged it would not be scientific to assume you can project it back to single nucleotide replicators that existed 9.7 billion years ago. Finally, biologists have only started to understand what is and what is not functional within the human genome. Therefore, we cannot assume that measuring genome complexity based off of our current understanding of functional non-redundant nucleotides is useful.

Unfortunately the claim that life originated 9.7 billion years ago might destroy the credibility of both the paper and the authors. I say unfortunately because within this paper the authors actually make a profound claim that I agree with:

The Drake Equation of guesstimating the number of civilizations in our galaxy may be wrong, as we conclude that intelligent life like us has just begun appearing in our universe. The Drake Equation is a steady state model, and we may be at the beginning of a pulse of civilization. Emergence of civilizations is a non-ergodic process, and some parameters of the equation are therefore time-dependent.

Recently I wrote about why I think it is highly probable that we are the first intelligent civilization to develop in our galaxy. My main reasons for thinking this are:

A) Our universe was not always well-suited for the evolution of life

B) Biological evolution requires billions of years of planetary stability

C) Biological evolution can produce trillions of species without ever selecting for high-intelligence and civilization

There are actually many more reasons why I think this is likely so I suggest reading my entry Intelligent Life in the Milky Way if you want to know more about it. Either way, my line of reasoning is certainly in line with Sharov and Gordon’s assertion that “intelligent life like us has just begun to appear in the universe.” Although they come at it from a slightly different perspective, I obviously find this assertion profound and compelling.

In the end I think Life Before Earth is worth a read if you are interested in learning more about Sharov and Gordon’s claims; but I am personally not sold. Biologists may never know the precise historic pathway of inanimate to animate matter and the specific materials present on the prebiotic earth, but I still think a 3.5 billion year origin for life is more likely than a 9.7 billion origin.

In the future biologists do need to demonstrate how biological evolution was able to produce highly complex prokaryotic genomes in a relatively short period of time. There could be a number of currently unknown reasons for this that do not require a single-nucleotide replicator with pre-galactic origins.

That is not to say that life could not have originated completely or partially from space. The idea that asteroids with complex organic compounds seeded our planet during the late-heavy bombardment 4 billion years ago is quite possible. But positing the chemical compounds necessary for life existed 9.7 billion years ago requires more evidence than a logarithmic scale with cherry picked data points.

Discuss this on Hubski or let me know what you think on Twitter!

 
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