RIVERSIDE, Calif. -- If we're looking at Mars, or planets in solar systems far, far away, how can we tell whether they support life? Researchers at the University of California, Riverside will share a $50 million grant from the NASA Astrobiology Institute (NAI) to help answer that question by studying ancient rocks on Earth to determine how oxygen developed in our atmosphere billions of years ago.
Specifically, UC Riverside's team will spend five years trying to map the different states of life on Earth from 3.2 billion years ago--when bacteria may have first begun oxygen-producing photosynthesis--to about 700 million years ago, about the time animals came on the scene, said UCR Distinguished Professor of Biogeochemistry Timothy Lyons, leader of the "Alternative Earths" team.
"The rate of discovery of exoplanets--planets from other solar systems--has been exponential, but we are a long way from the technology required to visit those planets, so the question is, what can we learn from early Earth to inform our exploration of life in the universe?" Lyons said.
"Earth is the only planet we know of that has life, so why look for life all over the universe if you don't, at the same time, explore how life evolved on our planet, and the signatures of that early life? It seems obvious, but it hasn't always been an easy sell to spend millions of dollars to look at 3-billion-year-old rocks from around the world to understand what might be on Mars or an exoplanet light years away."
UCR's team is one of only seven interdisciplinary teams selected to become members of the NAI, which is headquartered at NASA's Ames Research Center in Moffett Field, Calif. According to NASA, "average funding for each team will be approximately $8 million." The other six teams chosen to join the NAI are from NASA's Goddard Space Flight Center, NASA's Ames Research Center, NASA's Jet Propulsion Laboratory, the SETI Institute, the University of Colorado in Boulder, and the University of Montana in Missoula.
The idea behind the UCR-led study is to imagine what you could see if you were observing Earth remotely 3 billion years ago, Lyons said. What kind of evidence would confirm that our planet was habitable, and in fact teeming with life?
Liquid water and temperatures in the "Goldilocks Zone"--neither too hot nor too cold to sustain life--are already known to be important markers for habitability. The presence of oxygen can also be an indicator of complex life (such as animals that require oxygen), Lyons said. It isn't necessary for all life, but oxygen is a product, and therefore a signature, of life, he said, whether produced by plants or, as it was initially, by bacteria.
In fact, in its first 2 billion years or so, Earth didn't have any oxygen in its oceans or atmosphere.
The planet was constantly changing during its early history; it was hot, it was cold; it was mostly water and then it had land, continents which formed, grew and collided through plate tectonics.
Yet life existed through all those changes, Lyons said. People and other animals couldn't have lived on Earth 3 billion years ago, but there was life nonetheless--simple organisms like photosynthetic bacteria that ultimately caused oxygen to accumulate in our atmosphere about 2.4 billion years ago.
So if you were looking at Earth from afar, trying to determine whether there was life, what would you see in those early years? That's what Lyons' team will be trying to recreate, using clues from very ancient rocks collected by drilling or by sampling outcrops exposed at the surface.
Many of the rocks have already been collected from parts of Australia, Brazil, Canada, Russia and multiple spots on the African continent, including Zimbabwe, South Africa, Namibia, Gabon and Angola.
"South Africa and Australia, for example, have wonderful exposures of some very ancient rocks that are not heavily altered by time," Lyons said. "We also have some money to explore new areas with high potential for new perspectives, but we already have one of the best collections of materials ever assembled for a project of this sort.
"The kinds of rocks we look at are in layers, with the oldest at the bottom, and each of the layers is a page in the history of the ever-changing biology and chemistry of the oceans, land surfaces and the atmosphere on early Earth. We're trying to read that book, and if we find fossils in the rocks, great, but fossils are rare in rocks that old, so we'll be looking more at the chemical fingerprints left by the processes of life, as a way of telling us what was happening then on Earth."
These fingerprints, Lyons said, "are exactly those NASA is searching for on Mars and will use in its exploration beyond our solar system."
The Alternative Earths project will also study tectonic movement as a driver of large-scale environmental change and how that impacted the evolution of oxygen and life on Earth.
The UCR-led project will involve 19 scientists from 11 academic institutions, including Yale University (Lyons's alma mater), Georgia Institute of Technology (Georgia Tech), Arizona State University, J. Craig Venter Institute, Oregon Health and Science University, Pennsylvania State University and Rice University, two universities in Denmark and one in Belgium.
The two working group leaders are both former UCR graduate students who studied with Lyons--Noah Planavsky, assistant professor geochemistry at Yale, and Chris Reinhard, assistant professor at Georgia Tech's School of Earth and Atmospheric Sciences. They will work most closely with Lyons to coordinate the efforts of the widely dispersed team. UCR professors involved in the project are Andrey Bekker, Mary Droser and Gordon Love, all members of the Earth Sciences Department.
"This award is large by any standard, and with it comes terrific opportunity and responsibility," Lyons said. "It's the culmination of the 10 years I've spent at UCR, and the wonderful students, postdocs and colleagues I have worked with. It feels like a crowning achievement, because of the size of it, all the people involved, and the research foundation it builds on. I am delighted about the group we have assembled and the unique opportunities that lie ahead. It speaks to the strength of astrobiology at UCR and the legacy of that tradition. I couldn't be happier."
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