In what seems a cross between Jules Verne's Journey to the Center of the Earth and H. G. Wells' The Time Machine, researchers from the University of Rochester are burrowing deep underground into the most ancient regions of the globe to find the lost world where life began.
The endeavor, called The Mission to Early Earth, is part of the NASA astrobiology program. Astrobiology literally means "star life," but the NASA program is looking for life anywhere beyond our planet. To do that, however, an astrobiologist needs to know what he or she is looking for in the first place.
"If we're going to look for evidence of life on Mars or beyond, then we have to know what we're looking for," says Ariel Anbar, professor of earth and environmental science at the University. "There is so much we don't know about the origin and early evolution of life. What chemicals must be present? What kind of atmosphere helps life start? What are the factors we haven't even thought of? If you want to understand the probability of life being elsewhere, what that life might be like, and what the course of evolution might be, then you should be studying the only planet known to harbor life, and study the history of that planet."
Anbar is a member of one of NASA's astrobiology teams and a geoscientist, studying the planet to learn about its inhabitants. The greatest hurdle in trying to form a picture of what the world was like when life first formed is the scarcity of study samples. Old Earth simply doesn't exist anymore-on the surface. "We don't have a time machine, so we're stuck with old rocks," says Anbar. "But there aren't very many places you can find rocks that are billions of years old that haven't been ruined by exposure, so we're going to go subsurface."
"Subsurface" means drilling a couple hundred meters into the oldest known rock formations in the world. Anbar has just returned from Australia with his team on an exploratory mission to scout sites in parts of the Earth's crust that date to nearly 2.5 billion years old-more than halfway back to the Earth's birth-a time when the only life on the planet was bacteria. The NASA-funded trip to the Outback turned up a number of possible drilling sites that Anbar thinks may yield samples of the Earth's environment that have remained frozen in time. Though there are some sites in the world that boast rocks as old as 3.8 billion years, the Australian rocks are relatively undisturbed by weathering and geological processes.
Anbar's team is especially excited at the chance to pull organic molecules from the ancient rock bed. Such molecules can speak volumes about the organisms that produced them and should shed light on the course that evolution took in life's infancy. The first life forms may have had a biochemistry substantially different than today's, which means astrobiologists investigating Mars or other worlds would need to be looking for something totally unlike anything they may have assumed.
Anbar hopes to discover in what kind of environment astrobiologists should expect to find basic life. NASA hopes to launch space telescopes in the near future that will be able to pick out light from planets around distant stars. But what kind of telescope NASA builds will depend on what scientists are looking for-should it be tuned for an oxygen atmosphere or methane, or something else entirely? The answer to that will come from work like that of Anbar and his colleagues.
The Earth's basic chemistry was very different billions of years ago than it is now. It's widely accepted that the amount of oxygen in the atmosphere rose dramatically around 2.2 billion years ago, but there are a number of factors scientists don't know, not the least of which is, what completely changed the entire planet's atmosphere? Anbar explains that the classical argument is that that was the time period when photosynthesis evolved and created oxygen, but there's good evidence that oxygen-producing photosynthesis is much too old, leaving scientists stumped when trying to explain the oxygen surge. Scientists don't really know the exact living conditions on early Earth, and until they find evidence of the makeup of the atmosphere trapped inside ancient rocks, they'll have nothing but speculation.
"The odds are that we'll come across some surprises," says Anbar. "Some recent work by members of our team found that eukaryotes, the microbial line that humans came from, might have existed as early as 2.7 billion years ago. That's much earlier than a lot of people thought, which means there was a lot more diversification of biology back then. So maybe we'll learn that life was almost inevitable, a kind of by-product of our Earth's formation. Or maybe we'll learn that we're more rare and special than we ever imagined."
Anbar and the rest of the astrobiology teams' work is funded by the National Aeronautics and Space Administration (NASA).