Did Life Come Here From Mars?
It's still an intriguing theory, but still unproven.
- By Dirk Schulze-Makuch
- AirSpaceMag.com, August 29, 2013
If you’re old enough, you may remember the buzz created in 1996 when scientists claimed to have found fossilized life in a Martian meteorite called ALH84001—a discovery announced by the President of the United States. The scientific community, though, was far more skeptical, and is even more so today.
Shortly after that announcement, Joe Kirschvink from Caltech gave the Carl Sagan Lecture at the American Geophysical Union Meeting in San Francisco. I was there, along with many other students crammed into the giant auditorium, to hear him make the case that we might all be Martians.
Now another prominent scientist, Steve Benner of the Foundation For Applied Molecular Evolution, claims that we are likely of Martian origin. Why is that? Let’s go first to Kirschvink’s general arguments, then to the more specific one by Benner.
Imagine the inner solar system 4 to 4.5 billion years ago, when we believe that life originated on Earth (or maybe, we should now say, first arrived). Earth had a very violent birth. A body the size of Mars collided with the primordial planet and ripped pieces of its mantle apart, which re-formed to become—in part—our Moon. A hot magma ocean was the result, followed by alternating periods of extreme hot and cold—surely not the benign place we like to imagine for life to begin. Mars, on the other hand, was not the cold, dry, radiation-bathed place it is now, but a rather more pleasant world, with abundant water on its surface, a much thicker atmosphere, and even an occasional rainstorm. Perhaps Mars was a better place for life to originate?
Let’s continue the thought experiment spurred by the claimed fossils in a 4.5 billion-year-old Martian meteorite. Could Martian organisms possibly have survived the ejection from Mars, travel through space, and entry into Earth’s atmosphere? Research along this line has shown that the answer is a resounding yes. The interior of ALH 84001 was never heated above 50 degrees C (122 F)—well below sterilization temperatures.
Now Steve Benner claims that the element molybdenum, which appears to be important for the origin of life because of its catalyzing properties—meaning that it can enhance chemical reactions and is used by most organisms for that purpose— could have been available for chemical reactions on the surface of early Mars, but not on Earth. Why? Because Earth’s surface was oxygen-poor at that time, with an atmosphere that inhibited oxidation, and molybdenum is only soluble in the oxidized state. The Martian surface had become oxidized earlier in time, and was in that state presumably during that early phase when life would have originated.
This clearly is a hypothesis to keep in mind for the future. But it is by no means certain that life developed this way. From a geological viewpoint, any planet has a multitude of environments, not just a single one; the Sahara desert is not representative of the entire Earth. There could very well have been some oxidized zones on Earth 4 billion years ago, and Mars, with its thicker atmosphere, probably was more reducing than it is today. Furthermore, even though there are reasons to believe that molybdenum plays an important role in enhancing the transition toward life, it is not proven that without it, life would not have originated. Finally, many scientists think that life began at hydrothermal vents on the ocean bottom—and sorry, in this regard Earth trumps Mars, as it had, and still has, much more water.
Let’s face it. We know pathetically little about the origin of life, anywhere. And if it did begin on Mars and was later transferred to Earth, which clearly is a possibility, we don’t gain much by moving the point of origin, because environmental conditions on early Earth and early Mars were in many respects quite similar.
I’m sure my physicist friends get a big laugh. Those guys know what happened within a fraction of a second after the Big Bang, but we still know very little about how life originated on Earth. We know some of the steps that must have occurred, but there is no convincing hypothesis for how it all came together, and no one dares to think we can reproduce it in a lab. So what should we make of this new claim? People like Steve Benner should be applauded for putting forward new ideas, but we are still light years from solving the puzzle.
Dirk Schulze-Makuch is a professor of astrobiology at Washington State University, and has authored or co-authored seven books related to the possibility of life in the solar system and beyond.