Most Convincing Evidence Yet that Mars Supported Life
A lot of intriguing evidence has been collected over the years in support of the idea that life once existed on Mars. No definitive proof has been found, in the form of indisputable fossil evidence, for example. But it is known that Mars was once a watery world, and the existence of liquid water on the surface of a planet is the primary requirement for life to evolve.
Ample evidence has revealed that water once ran across the Martian landscape freely and in multiple locations. Liquid water can be found even now on Mars, at significant depths below the planet’s surface. Frozen water is located closer to the surface, and in impressive amounts. Much of this is no doubt the remnants of water that once formed Martian lakes or rivers.
The existence of liquid water on Mars, alone, wouldn’t guarantee it was inhabited. In fact, for a long time it was believed that surface water on Mars would have been highly acidic and therefore incapable of supporting living creatures.
However, a 2013 discovery by NASA’s Mars Rover Opportunity proved that at least some of the water that ran across the surface of Mars in ancient times carried a neutral pH , which means it was benign and could be consumed. This was an extremely significant finding by the Opportunity rover, since it proved that water quality on Mars in the distant past would not have been a barrier to the evolution and development of living species.
During this mission, the Opportunity Rover spent significant time exploring and taking samples within a 14-mile-wide crater named Endeavor. The Rover uncovered samples of clay minerals in an ancient rock sample on the rim of the crater, and after performing an analysis scientists realized that this particular type of clay could only be produced by water that was not acidic.
“This is water that you could drink,” declared Steve Squyres, a Cornell University professor who was the lead investigator on the Opportunity rover project. “This is water that was probably much more favorable in its chemistry, in its pH, in its levels of acidity ... for the kind of chemistry that could lead to the origin of life.”
It is believed that clays were generated by neutral-pH water flowing on the Martian surface 3.5-4 billion years ago, before the planet’s atmosphere was annihilated and it went through a period of significant cooling. Craters are good places to find these ancient clays, since the impact of the objects responsible for craters will inevitably excavate and rock and soils that were buried beneath the Martian surface in ancient times.
These findings have helped scientists piece together the conditions that once existed on Mars, and to understand how it made the transition from a warm and wet world to the frigid, dry desert we know today. They also provide confirmatory evidence for scientist convinced that life may have been present on Mars a long time ago.
“The fundamental conditions that we believe to be necessary to life were met here,” is how Squyres summarizes the Opportunity findings.
This, of course, does not prove that life existed on Mars billions of years ago. But it does show that the continuing search for fossil evidence, or even for living organisms in underground Martian reservoirs, is not a waste of time.
While the Opportunity discovery was significant because of what it revealed about water acidity on Mars, this is not the only instance where clay has been found in Martian craters. In fact, clay deposits in these locations are common.
In a 2015, Brown University geologists Ralph Milliken and Vivian Sun studied Mars rover imagery collected from 633 craters on multiple exploratory missions. On 265 of these they found evidence of clay deposits . After surveying the surrounding geology, they determined that 65 percent of these deposits were uplifted from the bedrock by meteor strikes responsible for the creation of the craters. This meant they had been created during the Noachian period, which encompassed the time when Mars was warm and wet more than 3.5 billion years ago.
But the remaining 35 percent of clay deposits appeared to be much younger in age. This has significant ramifications, because it suggests that liquid water continued to flow on Mars well beyond the end of the Noachian period.
“What this tells us is that the formation of clays isn’t restricted to the most ancient time period on Mars,” Milliken explained. The Brown scientists weren’t able to determine exactly when these clays were created, but it is clear they are much younger than the other samples observed and analysed.
Water has a long and interesting history on Mars, and its persistence on the surface increases the odds that it may have once hosted life.
A Speculative History of Evolution on Mars
Estimates are that the Martian climate was much warmer four billion years ago. It had an atmosphere that was much thicker and was able to capture the Sun’s energy and use it to heat its surface. Liquid water is known to be one of the necessary precursors to the evolution of life, and it is entirely possible that Mars’s long-lost lakes, rivers and oceans were teeming with microorganisms and other creatures that live and thrive in a marine environment.
Assuming, for the moment, that such life existed on Mars, the next obvious question is, did life also exist on land? If we assume evolution began in a watery environment, as it did on Earth, would there have been time for some creatures to crawl out of the sea and develop the capacity to survive in the open air?
If we extrapolate what we know about the development of life on Earth, it seems the answer to this question is ‘no, there wasn’t enough time.’
Like Mars, Earth was much warmer four billion years ago. The solar system formed only about 500 million years before that, and in a young solar system temperatures will be elevated everywhere, including on the surfaces of its planets.
Water ran freely and easily on both planets at that time, and readily collected where the geology was favourable. Each world was in the process of being shaped and formed by rampant volcanic and seismic activity, much of which occurred under the ocean and which helped create rich, hot stews where primitive microorganisms could evolve.
The first life forms on Earth made their appearance around 4.1 or 4.2 billion years ago. After that it took another 1.5 billion years or so for microorganisms to develop the capacity to survive on land. Evolution on land and in the sea continued slowly from that point on: it took approximately two billion more years for land-based plants and animals to develop (which is less than 800 million years ago from now).
If we assume a similar course of evolution for Mars, it seems clear that life never would have had the chance to evolve beyond a primitive, unsophisticated level. The devastating event that ripped away Mars’s thick atmosphere would have stopped evolution in its tracks, giving life no chance to take any further steps.
An Alien Home Base?
While evolution’s slow path would seem to rule out indigenous civilizations on Mars, there could be another possibility. Alien travelers visiting our solar system billions of years ago might have found Mars to be a more hospitable environment than Earth. Temperatures on Mars four billion years ago might have been less extreme than on Earth, since it was farther from the Sun. If alien explorers (a.k.a., ancient astronauts) were around, they might have used Mars as a home base.
It is of course unknown whether we were visited at that time by extraterrestrials. But if by some chance they were around, buried deep beneath the Martian surface there could be artifacts to prove they were there.
Top image: An illustration of astronauts on Mars. Credit: elenaed / Adobe Stock
By Nathan Falde