MadSci Network: Evolution
Query:

Re: radiation and evolution at varying ocean/eartth depths

Date: Sat Jan 21 19:12:33 2006
Posted By: Andrew Karam, Assistant Professor
Area of science: Evolution
ID: 1137848188.Ev
Message:

Boy, Jason – your question is very closely related to what I did my MS and Ph.D. research on – it's nice to know that at least one other person is interested! So…

First, you are correct that water and rock will provide very good shielding from cosmic radiation. But, for most of the history of the earth, cosmic radiation has not been a serious risk. UV was a significant factor until about 2 billion years ago, because the earth's atmosphere had no oxygen and, therefore, no ozone layer. Charles Cockell has calculated that the DNA damage from UV was as much as 1000 times higher in the distant past than today in areas exposed to UV. And soil, deeper water, and nocturnal lifestyle would all protect against those. But other cosmic radiation – charged particles from the sun, cosmic rays from supernovae elsewhere in the galaxy, etc have never really been a risk to life on earth because the earth's atmosphere and our magnetic field help protect us from them.

Something else that's interesting, but so far has not been formally looked into is that an organism's potassium concentrations may be related to rates of evolution. About one one-hundredth of one percent of natural potassium is radioactive, and every living organisms uses potassium as part of its natural biochemistry. So every living thing on earth gets some radiation exposure from internal potassium. Interestingly, some of the organisms with the lowest potassium concentrations also seem to have very slow rates of evolution – in particular, the horseshoe crab and an obscure shellfish (a type of brachiopod called "Lingula") are both virtually unchanged (evolutionarily speaking) in several hundred million years, and both have remarkably low levels of potassium. Right now, this is simply an interesting observation – my research was re-routed before I was able to check on this formally. Maybe someday…

Finally, I have done a little work with a colleague (Steve Leslie at the University of Arkansas at Little Rock) on whether or not changing radiation dose rates over time may have affected rates of evolution. We think that it has, and that evolution may have proceeded faster in the past, when radiation levels were significantly higher than they are today.

There is not much on-line about the radiation angle of changing rates of evolution due to changing radiation levels with time. For related information, you might try doing a Google search using the words "molecular clock" – this will turn up a whole bunch of sites. If you look under "molecular clock karam", you will turn up some references to the work Dr. Leslie and I have done in this area. Finally, if you have access to a university library, you might be interested in a series of papers by Leslie and I on how terrestrial radiation levels have changed over the history of life on earth – in particular, we have published 4 or 5 papers in the journal Health Physics between 1999 and 2002 or 2003 on these topics. Happy reading!


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