|Evolution in the News - July 2019|
|by Do-While Jones|
Is methane on Mars a sign of life?
Some scientists are really “excited” about methane on Mars because they think it might be an indication of life on Mars. They think that if there is (or was) life on Mars, it must have evolved there, proving that life evolved on Earth, too. It is flawed logic—but when it comes to evolution, most of the logic is flawed.
The article that first caught our attention was titled “Life may have come to Mars early” on page 9 of the 29 June, 2019, issue of New Scientist. That title implies that there is no question there was life on Mars. The only question is when it evolved there.
It was hard to find that article on-line because New Scientist changed their misleading title in the magazine to a different misleading title on-line. It is, “Mars meteorite assault stopped 500 million years earlier than thought” in the on-line version. Regardless of the title, the print version and on-line version of the article both said,
A period of intense meteorite assaults on the inner solar system may have stopped far earlier than we thought. Now there’s evidence to suggest that giant asteroid and comet strikes on Mars stopped 4.48 billion years ago, allowing it to develop conditions favourable to life as early as 4.2 billion years ago. It overturns a previous suggestion that the inner solar system, including Earth and the moon, continued to be heavily hit by meteorite impacts – a period known as the Late Heavy Bombardment – until around 3.8 billion years ago. 1
They used to think the Late Heavy Bombardment ended 3.8 billion years ago. Now they think it ended 4.3 billion years ago, therefore life could have arisen spontaneously 4.2 billion years ago, which is 500 million years earlier than previously thought—as if an extra 500 million years would make the impossible origin of life more probable. What is the evidence?
Desmond Moser at the University of Western Ontario, Canada, and colleagues have analysed meteorites thought to come from Mars’s southern highlands. The specimens are pieces of Mars’s crust which were knocked into space by a collision, and have since fallen to Earth as meteorites. Around 120 of these have been recovered to date. 2
Their estimates of conditions on Mars 4 billion years ago are based on rocks found recently on Earth, which they believe were knocked so far into space when something smashed into Mars that those rocks fell to Earth because they were more strongly attracted by Earth’s gravity than Mars’ gravity. They even think they know exactly where on Mars those meteorites came from. How can you argue with crazy logic like that?
You might wonder, what does meteor bombardment have to do with the origin of life?
The massive impact on Mars would have been a “globally sterilising” event, he [Desmond Moser at the University of Western Ontario, Canada] says. But it may also have helped to establish habitable conditions by accelerating the release of water from the planet’s interior. 3
How do we even know there was a heavy bombardment?
But the evidence for the Late Heavy Bombardment – a specific period of heavy asteroid strikes – is diminishing, she [Michele Bannister of Queen’s University Belfast] says.
“The Late Heavy Bombardment is an idea that was originally put together because of the way that the crater record on the moon was interpreted,” she says. 4
In other words, it is “lunacy.” The idea that giant asteroids brought water to the surface of Mars 4.48 billion years ago is based on craters on the Moon.
What does this speculation about asteroids striking Mars have to do with methane on Mars? Nothing, really—except when researching professional literature for the basis for the New Scientist article, I stumbled across a recent article in Nature which was titled, “Record methane level found on Mars” in the print journal, but titled, “Mars rover detects ‘excitingly huge’ methane spike” on-line. It said,
Planetary scientists avidly track methane on Mars because its presence could be a sign of life on the red planet. On Earth, most methane is produced by living things, although the gas can also come from geological sources such as chemical reactions involving rocks. 5
This led to yet another article in Nature, titled, “Aeolian abrasion of rocks as a mechanism to produce methane in the Martian atmosphere.” The title seems to indicate that Aeolian abrasion (wind erosion) causes methane to be released from Martian rocks. But, when you read the article, you will find the opposite conclusion.
… we suggest that aeolian abrasion is an unlikely origin of the methane detected in the Martian atmosphere, and that other methane sources are required. 6
This led us to an even earlier article.
Scientists have been catching hints of methane in the Martian atmosphere for 15 years using Earth-based telescopes, Mars orbiters and NASA’s Curiosity rover. As evidence of the gas has accumulated, the debate over its origin has intensified. “Nearly 95% of all the methane in the Earth’s atmosphere originated from current and past biology,” says Sushil Atreya, a planetary scientist at the University of Michigan in Ann Arbor. “So, it is natural to ask whether methane on Mars is also of biologic origin.”
The gas’s presence on Mars has surprised researchers, because chemical reactions in the atmosphere should destroy any methane molecules there within a few centuries. A measurable methane level suggests that an active source must be replenishing the gas. 7
This isn’t evidence of life on Mars millions of years ago because all that methane would have dissipated by now. There are two possibilities. (1) There is life on Mars producing methane now. (2) Methane is being produced through some geologic process now. Since no other detector has found life on Mars now, the first option isn’t likely.
Curiosity now routinely detects a background level averaging 0.5 parts per billion (p.p.b.) of methane in the atmosphere (by contrast, Earth’s level is about 1,875 p.p.b.). But the Martian concentration changes unexpectedly over time, says Atreya. Observations have also suggested the presence of large plumes with concentrations of 45 p.p.b., and Curiosity has detected burps of around 7 p.p.b. that dissipate quickly. “We didn’t expect methane to be on Mars, and it shouldn’t be variable unless there is an active source and a vigorous sink,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena.
Researchers have suggested several possible sources. The peaks might come from subsurface chemical reactions between rocks and water, carbon-rich meteorites that enter the atmosphere, or from sudden releases from reservoirs beneath Mars’ surface. Most thrilling of all, the peaks could have a biological origin. “It’s really a mystery,” says Ehlmann. 8
They don’t know what causes the methane, and they don’t know what causes it to disappear. Methane on Mars is neither proof that there is life on Mars now, nor is it proof there was life on Mars in the past. It certainly isn’t proof that life began on Earth through abiogenesis.
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New Scientist, 24 June 2019, https://www.newscientist.com/article/2207355-mars-meteorite-assault-stopped-500-million-years-earlier-than-thought/
5 Alexandra Witze, Nature, 27 June 2019, “Record methane level found on Mars”, page 420, https://www.nature.com/articles/d41586-019-01981-2
6 Safi, et al., Nature, 3 June 2019, “Aeolian abrasion of rocks as a mechanism to produce methane in the Martian atmosphere”, https://www.nature.com/articles/s41598-019-44616-2
7 Nisha Gaind, Nature, 23 April 2018, “Mars probe poised to solve red planet’s methane mystery”, https://www.nature.com/articles/d41586-018-04948-x