wpainter at vnet.ibm.com wrote:
: What are the current estimates on the total number of species of plant and
: animal life in the world today?
Oops. In my first response I did not notice that you were only
interested in plants and animals, not fungi, eubacteria, archaebacteria
and other life forms. We do have fairly good estimates of plant and
animal species diversity. I don't have the number handy though...
Anybody else?
Or are you really interested in all types of organisms?
A reference I do have handy is TIMESCALE by Nigel Calder. It
says that life is estimated to have started 4 billion years ago, the
first photosynthesis was about 3.9 billion years ago, but the first
bluegreen algaes evolved about 1.6 billion years ago and true plants
(eukaryotic photosynthesis) evolved about 1.3 billion years ago.
Thus, more evolution (2.7 billion years) took place before the
arrival of "plants" than afterward (1.3 billion years). Most of what
people think of as evolution (the rise of the vertebrates) is only very
recent, taking place over the last 0.5 billion years.
It is likely that point mutations in DNA occurred at a higher
rate in the first 1 or 2 billion years than it does today, because life
evolved more accurate polymerases and better DNA repair machinery. But
it seems that the advent of sexual reproduction (about 1 billion years
ago) has had a very large impact on the rate of evolution.
--
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* Brian Foley * If we knew what we were doing *
* Molecular Genetics Dept. * it wouldn't be called research *
* University of Vermont * *
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