Saturday, April 21, 2012


I posted a while back about Fermi's Paradox and Geoffrey Miller's excellent hypothesis; that it is caused by "computer games not atomic weapons". Another hypothesis is that intelligent life from elsewhere "seeded" Earth with life. There is at least one little data point in support of this theory:

Crick and Orgel further suggested that directed panspermia might help resolve one or two anomalies in the biochemistry of life-forms on Earth. One of these was the puzzling dependence of biological systems on molybdenum. Many enzymes, for example, require this metal to act as a cofactor. Such a situation would be easier to understand if molybdenum were relatively abundant on Earth. However, its abundance is only 0.02% compared with 0.2% and 3.16%, respectively, for the metals chromium and nickel, which are chemically similar to molybdenum. Crick and Orgel commented: If it could be shown that the elements represented in terrestrial living organisms correlate with those abundant in some types of star-molybdenum stars, for example-we might look more sympathetically on "infective" theories.
I was reading a paper about The distribution of elements in cells:
"With the advent of dioxygen the role of selenium has changed to that of a catalyst for the removal of peroxides and of iodine. Once again the special switches in chemistry of several elements with the coming of dioxygen suggest that evolution does not depend upon random mutation but that it operates following stress due to the environmental changes organisms suffer, see Section 9.1."
The availability of individual elements in the biosphere, especially in biologically accessible forms, has varied throughout the Earth's history; especially in response to increasing oxygen levels. In response to this, organisms have shifted the mix of the elements that they use to build themselves and mediate chemical reactions.

1 comment:

CP said...

In 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their oxidized nitrogen suitable for making organic nitrogen compounds, or the organics themselves (like proteins) from prokaryotic bacteria.[49][50][51] The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42− is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water. Once oxygen made by early life appeared in seawater, it helped dissolve molybdenum into soluble molybdate from minerals on the sea bottom, making it available for the first time to nitrogen-fixing bacteria, and allowing them to provide more fixed usable nitrogen compounds for higher forms of life.