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).
