Now that Curiosity has landed safely in Gale Crater and directly upon an alluvial fan at the base of Mount Sharp–a mountain likened in its strategraphic layering to the Grand Canyon, my imagination is vexed. I want the rover to find FOSSILS.
Am I being dreamy and silly to hope for this? It’s hard to say. But one thing is certain: if Mars consists solely of microfossils (single-celled organisms), then there will be no discovery of them by Curiosity because its microscope is not of sufficient magnification to detect them. Curiosity has investigative tools for detecting evidence of microfossils and of life, but not to make a definite visual determination of life’s tiniest forms.
Experts, though sharing a general consensus that protists (single-celled organisms) probably once existed on Mars, are not terribly optimistic that multicellular life ever has.
Still, it’s possible. Here’s National Geographic from November 3, 2010:
Victor Baker, a planetary scientist and geoscientist at the University of Arizona in Tucson . . . agrees that Martian groundwater had the potential to support life.
“There are subsurface environments on Mars, even today, which are undoubtedly not much different chemically, or [in terms of] temperatures and pressures, to subsurface environments on Earth that have life in them,” he said.
But when dreaming of Martian fossils, Baker cautioned, don’t expect to find the kinds most familiar to us on Earth.
“Whatever is an indication of previous activities of living organisms can be a fossil. It doesn’t have to be bones. It can be traces. It could be evidence of chemistry that one can tie back to a biological process,” he said.
“To expect that Mars would have achieved something like the Cambrian explosion“—Earth’s most intense burst of evolution—”would really be stretching it,” he added.
“But to expect that Mars might have [microorganisms] similar to what was characteristic life for most of Earth’s very early history is not too great of a stretch.”
Victor Baker’s cautious assessment about this matter is probably representative of the scientific community generally. As to the issue of whether there has been enough time for multicellular life to evolve on Mars, this (also from National Geographic) seems hopeful:
Recent high-resolution images taken by NASA’s Mars Reconnaissance Orbiter suggest Mars may have stayed wet a billion years longer than most previous estimates, scientists report.
Researchers say they have identified water-carved features that date to the Hesperian Epoch, 3.7 to 3 billion years ago.
The time frame is far more recent than the period scientists most often associate with the presence of liquid water on Mars—the Noachian Epoch, which spanned the first billion years on the red planet from about 4.6 to 3.5 billion years ago.
Catherine Weitz is a senior scientist with the Tucson, Arizona-based Planetary Science Institute. She and her colleagues spotted the water-shaped features along plains next to the Valles Marineris, a long system of canyons at the Martian equator (photo: a canyon in the Valles Marineris).
“This was a big surprise, because no one thought we’d be seeing these extensive fluvial systems in the plains all around Valles Marineris that were formed during the Hesperian Era,” Weitz said in a press release.
“Everyone thought that by then the climate had pretty much dried out.”
And back in 2010, the Washington Post reported that NASA’s Mars meteorite team was again asserting that the controversial ALH84001 Mars meteorite, 4.5 billion years old, does indeed appear to possess microfossils and so presents strong evidence that life once existed on Mars:
“All the criticisms of our original paper got widely distributed, but when we did the work to prove the critics were wrong, it hardly made a ripple,” he [NASA’s David McKay] said at a conference interview. “We’re now in a position to say we’ve knocked down all the criticisms — and our biological explanation is the one left standing.”
Mars itself is 4.6 billion years old, and thus, if the NASA team is correct, life on Mars appeared in the first 100 million years of the planet’s existence. And if Mars had substantial amounts of flowing water on its surface up until 3.0 billion years ago (see above), that gives a window for the evolution of unicellular and perhaps multicellular organisms and their radiation of 1.6 billion years. That sounds like a lot of time, but it may not be enough. Earth itself spent perhaps 3 billion years in the single-cell stage. But maybe Earth spent so much time in the single-cell stage because the oceans on Earth are vast and so generated less direct competition for resources. Maybe on Mars multicellular life evolved more quickly because of issues of ecological isolation and competition.
But we’ll see what Curiosity discovers. If you haven’t, by the way, watched this full 11 minute film from NASA yet, it’s worth it.