Earth’s most ancient fossils are hard to find. Some scientists think a few of the earliest fossils might still be preserved in Earth rocks blasted to the moon by an asteroid or meteor. Others believe much of the evidence has been erased forever by the constant heat and pressure of plate tectonics.
But learning as much as possible about the earliest life on Earth is probably the best starting point for trying to find life somewhere else, said Roger Buick, a paleontologist who became the first faculty member hired specifically for the University of Washington’s pioneering graduate program in astrobiology. He also is an associate professor of earth and space sciences.
"The earliest organisms were presumably very simple, both in their structure and their chemistry," he said. "The evidence we’re used to seeing for modern life may not be a good guide for what to look for in earliest life."
As a doctoral student nearly two decades ago, Buick discovered stromatolites, or mounds of sedimentary rock, formed by microbes 3.5 billion years ago in western Australia. Those mounds remain the oldest visible evidence of life on Earth.
Buick suggested that using basic techniques to search for the simplest evidence of ancient life on Earth is the best approach to finding evidence of life elsewhere. That is a message he delivered today at the American Astronomical Society’s annual meeting in Seattle during a session called "The Biology of Astrobiology for Astronomers." There are a variety of difficulties associated with searching for early life based on what we know of biology and geology, he said, yet both disciplines must be involved if we are to be successful in the search for life elsewhere.
"We have to go from what we know, but we also must have an open mind because we might be surprised by what we find," he said. "We have to be hypercritical so that we’re not misled by superficial resemblances to what we know."
It will be a tough chore for astrobiologists to turn their field into a self-sustaining endeavor because for so long science fiction has made the idea of life away from Earth a fanciful notion of all sorts of intelligent aliens, Buick said.
"It will take a lot of work to turn it from science fiction into science, and because it is so interdisciplinary it’s going to require a rethinking of how science is done," he said.
The UW started the first graduate program in astrobiology four years ago with a National Science Foundation grant for graduate education and research. That later was supplemented by a major award from the National Aeronautics and Space Administration’s Astrobiology Institute and money from the UW. The curriculum involves 11 degree programs – including astronomy, microbiology, chemistry and oceanography – and graduates receive degrees from one of those programs with an endorsement certificate in astrobiology. Graduates will have broad, interdisciplinary knowledge, the kind many of their professors are just starting to gain now.
Buick said fossil evidence of early life, whether from Earth or somewhere else, could be so tiny that it is at the limits of – or beyond – current capabilities in optic microscopic resolution. Those life forms might have existed without hard bodies, so fossil evidence would be exceedingly difficult to find and might consist only of poorly preserved organic polymers.
He noted there are three instances – two in Greenland and one in Australia – in which evidence for life on Earth was discovered that was as old or older than what he found. But in two of the cases the evidence is not clear-cut and there are ongoing scientific disputes about the meaning of the data. To resolve these arguments, he said, it is important for scientists to understand how signatures for biological life can be altered or erased from rocks, primarily by heat and pressure.
To sort out the terrestrial evidence and to apply it to the search for simple extraterrestrial life will involve many, if not most, of the existing scientific disciplines, each adding bits of knowledge to crystallize the science of astrobiology, Buick said.
"The bottom line is that we don’t know much yet, but it’s going to be a huge amount of fun finding it out," he said. "And everyone has something to contribute."
University of Washington. January 2003.