Then, during the Ordovician period, which began around 490 million years ago, many new species sprang into being. The first coral reefs formed during that time, and the first true fish swam among them. New plants evolved and began colonizing land.
If you picture the evolutionary tree of life,' most of the main branches existed during the Cambrian, but most of the smaller branches didn't get filled in until the Ordovician, Saltzman said. That's when animal life really began to develop at the family and genus level. Researchers call this diversification the Ordovician radiation.
The composition of the atmosphere has changed many times since, but the pace of change during the Cambrian is remarkable. That's why Saltzman and his colleagues refer to this sudden influx of oxygen during the SPICE event as a pulse or burst.
After this pulse of oxygen, the world remained in an essentially stable, warm climate, until late in the Ordovician, Saltzman said.
He stopped short of saying that the oxygen-rich atmosphere caused the Ordovician radiation.
We know that oxygen was released during the SPICE event, and we know that it persisted in the atmosphere for millions of years -- during the time of the Ordovician radiation -- so the timelines appear to match up. But to say that the SPICE event triggered the diversification is tricky, because it's hard to tell exactly when the diversification started, he said.
We would need to work with paleobiologists who understand how increased oxygen levels could have led to a diversification. Linking the two events precisely in time is always going to be difficult, but if we could link them conceptually, then it would become a more convincing s
|Contact: Matthew Saltzman|
Ohio State University