Did global cooling lead to marine life biodiversity?

BEIJING, July 28 (Xinhuanet) -- An explosion in
marine biodiversity that happened 460 million years ago could be the result of
global climate change, according to researchers.

Scientists from the INSU-CNRS Laboratoire
Pal¨¦oEnvironnements et Pal¨¦obioSph¨¨re (CNRS) Universit¨¦ Claude Bernard Lyon and
Australian National University in Canberra have found evidence of a progressive
ocean cooling of about 15¡ãC over a period of 40 million years during the
Ordovician, a geologic period extending from 490 to 440 million years ago.

Until now, this geologic period had been associated
with a "super greenhouse effect" on our planet. The results from this study were
published in the July 25, 2008 issue of Science.

The researchers found that marine water at the
beginning of the Ordovician (480 million years ago) was very warm (around 45¡ãC),
too warm for complex living organisms to develop. The temperature measurements
were obtained from fossils of primitive eels called conodonts, whose geologic
age was known by the researchers.

They analyzed a mineral found in these eels' skeleton
for changes in the ratio of two oxygen isotopes, which is dependent on the
temperature of the ocean water in which the animals lived. The early Ordovician
was a time when our planet's atmosphere was still very rich in CO2, causing a
strong greenhouse effect and therefore very high ocean temperatures.

The progressive ocean cooling coincided with an
explosion in marine biomass and biodiversity (the number of genera and families
jumped by a factor of three to four). This event took place during the Upper
Ordovician, around 460 million years ago, when ocean temperatures became
comparable to those of present day equatorial waters. Not only did marine
animals diversify, but their range also spread to the seafloor, and the first
coral reefs appeared.

The cooling of the oceans was coupled with
atmospheric cooling, indicating that a global change in climate took place. This
could have played a major role in the unprecedented increase in biodiversity
seen in the Ordovician, which opened the modern era of diversity and complexity.

(Agencies)