Narrator: This is Science Today. When researchers want to learn more about events that occurred here on Earth billions of years ago, they look for chemical clues in ancient rocks. Chris Reinhard, a geoscientist at the University of California, Riverside helped analyze 2.5 billion-year-old black shales from Western Australia. These rocks give scientists more insight into early Earth.
Reinhard: We're trying to look at when oxygen first started to accumulate in Earth's atmosphere.
Narrator: The shales they're studying essentially represent fossilized pieces of the ancient seafloor.
Reinhard: It's pretty stunning and when we work on this really old stuff, we sort of work on the 2.2 to 2.4 billion year time scale, but that .2 is 200,000 million years, which is a really staggering amount of time! And so that's really an important part of doing all this, I think, is sort of an appreciation for how the Earth evolves through time and really what sort of staggering time frames we're looking at.
Narrator: For Science Today, I'm Larissa Branin.