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Welcome to The Lotus Position, an intermittent collection of extempore navel gazings, ponderings, whinges, whines, pontifications and diatribes.

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The Budapest Office - Castro Bisztro, Madach ter

The Budapest Office - Castro Bisztro, Madach ter
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Thursday, 27 March 2008

Keep taking the molybdenum?

It's an interesting piece of work. Apparently "scientists" (quotes allude to my irritation with the increasingly vapid use of the word scientist) - including at least one proper biogeochemist, Prof Timothy Lyons) - have reconstructed some aspects of Earth's ocean chemistry between 2GY and 0.5GY BP (see Science Daily) and infer that a lack of oxygen and molybdenum during this time was responsible for delaying animal evolution. [University of California - Riverside (2008, March 27). Reason For Almost Two Billion Year Delay In Animal Evolution On Earth Discovered; paper due to appear in the March 27 issue of Nature]

Whilst intrigued that, according to the (online press) article the diversity of early single-celled life forms remained low from the beginning of oceanic surface oxygenation circa 2.4GY BP, and that "their multicellular ancestors [sic], the animals, did not appear until about 600 million years ago" the point is generally well made: molybdenum is essential in to the nitrogen fixation process in modern nitrogen-fixing bacteria - too little molybdenum = too little fixation, and eukaryotes deprived in turn of accessible nitrogen cannot thrive.

A neat explanation, but 2 billion years is an awfully long time and I can't help thinking that evolution would have rapidly favoured any organism that found another way to fix nitrogen.

So the proposed molybdenum solution to the question "Why was multicellular life so slow to get going?" actually raises an even more significant question: why is molybdenum so indispensable that nothing else would do?

I find it very hard to believe that Darwinian micro-evolution couldn't have fixed things (excuse the pun) in the available time so I have to doubt that the dearth of molybdenum was the fundamental limiting factor. Besides which, diversity does not equate to quantity - so early nitrogen-fixers may have been few in kind but more than plentiful enough to support the needs of eukaryotes... given the molybdenum available, what biomass was supportable?

Of course the rest of the findings on oxygen levels, obtained by using molybdenum as a proxy for oxygen concentration, remain valid but the point about molybdenum as an essential and evolution-limiting micronutrient seems a bit wobbly to me.

Geochemical-Stuff Rocks nonetheless