'We're All Martians, Scientist Claims," the Telegraph recently wrote. Similar articles showed up in newspapers and on websites around the world.
The scientist who inspired the headlines is a chemist named Steven Benner, a distinguished fellow at the Foundation for Applied Molecular Evolution in Gainesville. Headlines notwithstanding, Benner is not a wild-eyed UFO advocate claiming to have seen Little Green Men. Instead, he is one of the world's experts on the origin of life.
The cause for Benner's newfound celebrity is a lecture he delivered at a geology conference in Florence, Italy, on Aug. 29. During his talk, he challenged his fellow scientists to look hard at the evidence we have about how life began.
Depending on how you view that evidence, Benner argued, Mars might be a more likely place for life to have started than Earth. The best way to determine the answer, Benner argued, is to look for certain types of chemicals on both planets.
"I really don't have a dog in this fight," Benner said in an interview after he returned from Italy. "It could go either way and I would be equally happy."
Benner and his colleagues have amassed evidence for one potential path by which chemicals could have become living matter. Small organic compounds could have reacted with each other to produce string-shaped, self-replicating molecules. These strands, known as RNA, later combined into double-strands: the DNA in which we and other species encode our genes.
In experiments, Benner and his colleagues have demonstrated the occurrence of many of the reactions in this path. But they've also discovered roadblocks.
For instance, the precursors to RNA can bond in a lot of ways. While some reactions can lead organic molecules toward RNA, many others can turn them into gooey tar.
Benner and his colleagues discovered that minerals containing borate could help life overcome this obstacle. Binding to the precursors of RNA, borate blocks them from reacting in destructive ways, so they are much more likely to form compounds that could eventually give rise to life.
But even in the presence of borate, Benner and his colleagues have found, these precursors can't make some of the final changes that turn them into RNA. Recently the researchers found that molybdate minerals can react with the precursors to help them become RNA.
While this chemistry may work in the lab, however, it may not have worked on the early Earth. Robert M. Hazen, a mineralogist at the Carnegie Institution for Science and author of The Story of Earth, is among the geologists who have argued that it's unlikely that borate or molybdate were abundant then. Today, borate is found in deserts that formed after large seas evaporated. But deserts may not have existed 4 billion years ago. A number of studies suggest that the early Earth was covered in water and had few if any continents.
As for molybdate, it only forms in the presence of oxygen. The atmosphere of the early Earth appears to have been nearly oxygen-free.
At the moment, Mars looks more promising to Benner. The evidence gathered by satellites and rovers suggests that both oceans and continents existed early in the planet's lifetime. Under those conditions, borate might have formed.
In June, more evidence emerged that supports this idea. Studying a meteorite from Mars, scientists at the University of Hawaii reported that it contained high levels of boron, a component of borate.
The atmosphere of early Mars also shows signs of having contained oxygen, enabling molybdate to form. With a supply of both borate and molybdate, Mars might have been a favorable place for RNA to emerge, and for life to start. A giant impact could then have kicked up microbe-laden rocks, which later fell to Earth.
In his lecture, Benner did not present this argument as proof that we are Martians. Instead, he offered a way to organize our thinking about the origin of life. He displayed a series of linked questions that scientists should ask themselves.
The first question is, did life start out as RNA? If the answer is no — and some scientists believe that to be the case — then they have to grapple with a different set of challenges to explain the origin of life.
For scientists who do accept an RNA-based origin of life, however, they need to find chemistry to produce it.
Benner hoped his talk would provoke new research, and it is already has. Hazen, for example, is studying 3.8-billion-year-old rocks from Greenland to look for signs of borate that he may have missed elsewhere.
Benner hopes the search bears fruit.
"Then I have all the deserts I need," Benner said. "I don't have to go to Mars."
© 2013 New York Times News Service