If you looked in a mirror this morning, you may have seen a descendant of creatures from Mars. That is, if biochemist Steven Benner of the Westheimer Institute of Science and Technology in Gainesville, Fla. is right. "Life started on Mars and came to Earth on a rock," Benner declares. Today, at the European Association of Geochemistry's Goldschmidt Conference in Florence, Italy, Benner made what many in the origin-of-life debate call an interesting, but not convincing, new case for our martian heritage.
However and wherever life began, one thing is sure: Its first organic building blocks, called hydrocarbons, had a number of hurdles to clear before evolving into living cells. Fed with heat or light and left to themselves, hydrocarbons tend to turn into useless tarlike substances. And even when complex molecules like RNA (most biologists' best guess for the first genetic molecule) arise, water quickly breaks them down again.
Benner argues that those chemical hurdles would have been lower on early Mars than on young Earth. To begin with, early Earth was probably a water world, completely covered by oceans, but water covered only parts of Mars's surface. Moreover, he notes, rocks on Mars had a stronger oxidizing effect than rocks on Earth, so oxygen-bearing molecules would have formed more easily there. "This is established by observations today on both planets, as well as by models for how planets form," he says.
As a result, molybdates-molecules that contain molybdenum and oxygen-could have existed on Mars, but probably not on Earth. Like oxidized boron (which occurs in dry regions and would also have been rare on a water-covered early Earth), molybdates tend to prevent organic materials from turning into tar. Benner says laboratory experiments show that molybdates can convert certain organic molecules into ribose-an important component of DNA. "This is a fact," he says.