Spindle-shaped inclusions in 3 billion-year-old rocks are
microfossils of plankton that probably inhabited the oceans around the globe
during that time, according to an international team of researchers.
"It is surprising to have large, potentially complex
fossils that far back," said Christopher H. House, professor of
geosciences, Penn State, and lead author.
However, the researchers not only showed that these
inclusions in the rocks were biological in origin, but also that they were
likely planktonic autotrophs -- free-floating, tiny ocean organisms that
produce energy from their environment.