5. Too much molecular Hydrogen (H2) early in Mars’ history
New research by James Kasting, a planetary scientist at Penn State University, argues that early Mars was kept warm by a Carbon Dioxide (CO2)-Hydrogen (H2) atmosphere which in turn allowed for the running water thought to be needed to form Mars’ valley networks.
For 20 years, Kasting has been looking for ways that early Mars could have been warm enough to form those valleys. In a paper now in peer review, Kasting posits that a combined greenhouse effect from CO2 and H2 could have created these warm, wet conditions, some 3.8 billion years ago.
“The presence of significant amounts of H2 essentially requires that Mars was lifeless at that time,” said Kasting. “Organisms would probably have eaten the hydrogen if they were present. You can’t do [valleys] without a warm climate, and a warm climate is hard to produce. A CO2-H2 greenhouse can do it.”
Finally, there’s no obvious indication that life has played a significant role in modifying the landscape or inhabiting its surface.
Catling points to a lack of black shale as evidence that Mars has never had abundant photosynthetic life.
On earth, he says evidence for ancient microscopic life is visible to the naked eye in the form of black shales; fine-grained sedimentary rocks rich in dead microbe remnants. No such shales are seen on Mars.
“Had life been abundant,” said Catling, “you might expect them to be exposed by wind erosion every now and again.”
However, Bethany Ehlmann, a planetary geologist at Caltech, says unlike earth, Mars wasn’t able to sustain all of its habitats through time. Thus, she would expect life on Mars today to be hiding in hard-to-reach niches rather than exerting a strong control on the planet’s current chemistry.
“It’s going to be hard to tell without going there with a team of astronauts and a deep drilling rig,” said Kasting. “But my gut feeling is that Mars doesn’t have, and never did have, life.”