The UCR Department of Earth Sciences is the heart of one of seven science teams selected to join the NASA Astrobiology Institute in 2015. Distinguished Professor of Biogeochemistry Tim Lyons is leading the team of 21 scientists from 11 partner institutions, including Yale University, Georgia Tech, Arizona State, Oregon Health and Science University, and the J. Craig Venter Institute.

The Alternative Earths team has been awarded ~$7.5 million over five years to address the question of how Earth has remained persistently inhabited through most of its dynamic history. The idea is to look back in Earth history for direction in our search for life elsewhere—be it Mars, moons of Saturn, or worlds much farther away…

Why is it important?

There’s a serious buzz these days about the nearly continuous discovery of planets orbiting stars outside our solar system. The known number of these so-called exoplanets is already in the thousands, and hundreds of them are about the size of Earth. (One recently discovered Earth-sized exoplanet is just 39 light-years away!) Some of these exoplanets are the right distance from their host star to potentially harbor the key ingredient for life as we know it: liquid water. Within the next couple of years, new NASA missions, including the launch of the James Webb Space Telescope, will make it possible to peer into the atmospheres of these planets and see what they are made of. That’s when things will really get exciting.

Take Earth, for example. If you could view our planet’s atmosphere from many thousands of light-years away, you would see water. You would also see large amounts of free oxygen (O2) that derives entirely from photosynthesis. For Earth, O2 is a signature of life—a biosignature. Yet Earth was also inhabited at times when there was little or no O2 in the atmosphere. So what did the atmosphere look like back then? In the absence of O2, what biosignatures would there have been?

That’s what the Alternative Earths team is trying to figure out. It is conceivable that each of Earth’s widely varying planetary states translates to a particular atmospheric composition that could one day be detected on an exoplanet—and that one of these “Alternative Earths” could help prove the presence of life elsewhere in the universe.