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Chemical fossils push back the date for animal life to at least 635 million years ago


Fossils push animal life back millions of years: study
36 minutes ago
PARIS (AFP) - Animal life first appeared on Earth tens of millions of years
earlier than thought, according to a new study released Wednesday.


Oldest Fossil Evidence for Animals 
FoundBy Robin Lloyd, LiveScience Senior Editor
posted: 04 February 2009 01:00 pm ET

The oldest fossilized chemical evidence of animals has been unearthed in
Oman and reveals that tiny sea sponges were abundant 635 million years ago,
long before most of the planet's other major animal groups evolved,
according to a new analysis. 

This early life hardly looked like us, but some of the so-called demosponges
can be sizable today. Demosponges still make up 90 percent of all sponges on
Earth and 100 percent of Earth's largest sponges, including barrel sponges,
which can be larger than an old-style phone booth. 

The ancient demosponges - probably measuring across no more than the width
of a fork tine - were pinned down via fossilized steroids, called steranes,
which are characteristic of the cell membranes of the sponges, rather than
via direct fossils of the sponges themselves.   

"The fact that we can detect sponge steranes at all suggests that by the
Cryogenian Period [about 850 to 635 million years ago] demosponges were
ecologically prominent and there were abundant demosponges living on the
shallow sea floor," said geochemist Gordon D. Love of the University of
California, Riverside, who headed up the analysis detailed in the Feb. 5
issue of the journal Nature. 


Chemical fossils push back the date for animal life to at least 635 million
years ago
By Rachel Ehrenberg 
Web edition : 2:02 pm 
The findings, published in the Feb. 5 Nature, suggest that the ancient
ancestor of fully formed animals survived a massive glaciation that
enshrouded the Earth in ice at the end of the aptly named Cryogenian period
"Evidence of animal life from before the Marinoan," the severe glaciation of
635 million years ago, "is really something," says Jochen Brocks of the
Australian National University in Canberra. Brocks and Nicholas Butterfield
of the University of Cambridge in England coauthored a Nature commentary on
the new work.
Sponges, however, may have come on the scene before the Ediacaran period and
lived through it. The new analysis, led by organic geochemist Gordon Love of
the University of California, Riverside, documents the molecular remains of
a steroid from sedimentary rock deposited 150 meters below the end of the
Marinoan ice age. (Researchers debate when this ice age actually started.)
The steroid fossil, known as 24-isopropylcholestane, or 24-ipc, is the
geologically stable form of a steroid known today from the cellular
membranes of one of the three classes of sponges, the Demospongiae. A small
group of algae also make the molecule, but the ratios of 24-ipc to other
algal compounds rules algae out as a source
"Finding a molecule that was made by an organism, that means the
biosynthetic ability to make that molecule must have evolved earlier,"
Brocks says.

The new work fits nicely with molecular clock work dating the evolution of
multicellular life, says Peterson. It also ties in well with ideas about
ocean and atmospheric chemistry. These early sponges might have helped bring
about the oxygenation of the deep oceans, which then paved the way for more
life. Sponges are a dominant stationary animal in the Cambrian, but then
their presence seems to taper off,