Life originated as an oddity

Coming up with a theory for the origin of something so complex and ancient as life on Earth might seem to be at the pinnacle of hubris, yet such ideas are not uncommon. A novel slant on the ‘Big Question’ centres on how cells get their energy, rather than on trying to put together all manner of chemical prerequisites (Lane, N. 2009. The cradle of life. New Scientist v. 204 (17 October 2009) p. 38-42). Mike Russell began his career as a geochemist looking at hydrothermal mineral deposits and the intricacies of their formation, while at the University of Strathclyde, Scotland. He now works at NASA-JPL in Pasadena, California inspired by the views of a self-funded eccentric Cornish farmer, Peter Mitchell. Cell energetics, according to Mitchell, are about pumping protons through cell membranes to effect the oxidation and reduction fundamentals of metabolism; in short electrochemical gradients. That is now recognised by every cell biologist, though once it was considered absurd. Russell’s take on that novel truism is that the environment of life’s origin must have involved similar processes taking place in the absence of living cells, which inherited proton pumping. His choice is mineralised pinnacles full of foam-like voids that can act as minute chemical factories: not the famous sulfidic black smokers of ocean ridge systems, but cooler features formed of carbonates precipitated from alkaline sea-floor hydrothermal vents. The carbonate foam in ancient examples, well-known to Russell from their mineralisation, contains bubbles lined with iron sulfides. Sulfides are known to have catalytic properties; proteins in living cells that convert CO2 to sugars have Fe-S bonds at the core of their structure; alkaline hydrothermal vents emit hydrogen released by alteration of olivine in ocean-floor basalt to serpentine minerals; bubbles in carbonate foam look very like potential precursors to cells. To produce the first living cells, these features together in one enclosed space need 10 steps of quite simple chemistry. Except, that is, for nucleic acid production…

End-Permian crisis not so bad for ammonites

The greatest known mass extinction at the end of the Permian Period snuffed out 85% of fossil marine species. It is widely understood to have taken at least five million years for ecosystems to begin recovering, and some animal groups remained depressed for longer still, especially those living at or near the sea floor. Yet one group of cephalopods, the ceratidid ammonites, almost immediately began to thrive, despite the ammonoid sub-Class having been among the hardest hit groups (Brayard, A. et al. 2009. Good genes and good luck: ammonoid diversity and the end-Permian mass extinction. Science, v. 325, p. 1118-1121). Only three genera of ceratidids survived the cataclysm, but within 1-2 Ma there were almost 100 representatives. A similar swift recovery is shown by the completely unrelated conodont animals (now-extinct eel-like vertebrates whose teeth are generally the only parts to be fossilised). For such a success story to emerge by pure chance seems intuitively unlikely: for cephalopod  equivalents of Lazarus to go forth and multiply so nicely requires genes well-suited to the conditions that followed the mass extinction.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s