Was Ancient Mars Like Earth? How Mars Died while Earth Lived





Recent studies suggest that ancient Mars, like Earth today, may have had an oxygenated atmosphere and a plenitude of liquid water.

4 billion years ago, our world was a land of boiling oceans and rampant volcanic activity under a crushing atmosphere primarily consisting of carbon dioxide. Although the chemistry for life had already been established, the Earth’s surface was a hellish inferno, a world devoid of life. Meanwhile, ancient Mars showed great promise, with recent studies suggesting it was once more like Earth than we had ever imagined.

Today, Mars is a cold, dead world with an atmosphere barely more substantial than a typical laboratory vacuum. But, it wasn’t always this way. Some 4 billion years ago, Mars was in its Noachian geological period. Evidence suggest that, while Earth was truly inhospitable at the time, the Red Planet was home to oceans and an oxygenated atmosphere that may have warmed the planet enough to allow rainfall.

The earliest known life first gained a foothold on Earth some 3.7 billion years ago as the planet cooled, volcanism calmed and the Late Heavy Bombardment ended. However, as early life was developing on Earth, Mars steadily became a barren world. Mounting evidence suggests that, as Earth became habitable, Mars died, becoming the apocalyptic wasteland that we know today.

A Land of Lakes and Oceans

Mars’s Noachian Period spans 4.1 to 3.7 billion years ago while the inner solar system was undergoing the Late Heavy Bombardment, a period in which asteroid impact events were some 500 times more common than they are today. This, combined with geological activity promoted by the planet’s then dynamic interior, would have kept the surface warmer while also helping to create a denser atmosphere, which is exactly what happened on Earth at about the same time.

Areas of the Red Planet dating from the Noachian Period are of great interest to scientists today, since they’re the perfect hunting grounds for any fossils of organisms that may have thrived on ancient Mars. Although there’s still no evidence that life ever found a foothold there, it seems likely that all the requirements for microbial life were in place at the time.

Today, water generally cannot exist in liquid form on the surface of Mars, since the extremely low air pressure and temperatures cause it to boil away almost instantly. Nonetheless, NASA revealed evidence in 2015 that water does still flow on Mars, albeit briefly and intermittently in the lowest-lying regions of the planet during the summer. There’s overwhelming evidence that water once flowed abundantly, however, most notably in the enormous low-lying region of Acidalia Planitia in the northern hemisphere and the Hellas Planitia basin in the south.

Acidalia Planitia, now nothing more than a vast, dusty plain covering millions of square miles, was, according to the Mars Ocean Hypothesis, once home to a primordial ocean known as Oceanus Borealis. In addition, more than 200 lake beds from the Noachian Period have been identified by their distinct shorelines that appear to have been eroded by water activity long ago.

A Warmer, Oxygen-Rich World

Atmospheric oxygen first appeared on Earth during the Great Oxygenation Event some 2.45 billion years ago thanks to photosynthesising cyanobacteria. Recent evidence suggests that Mars had free oxygen in its atmosphere much earlier. Last year, NASA’s Curiosity Rover identified manganese oxide in Martian rocks, a chemical compound that’s either created by microbes or free atmospheric oxygen. Since it’s highly unlikely that Mars was habitable for long enough for any ancient life to truly thrive to the extent as it did on Earth, scientists have concluded that a combination of abundant surface water and atmospheric oxygen are the most likely culprits.

When the solar system was young, the terrestrial planets, such as Earth and Mars, were alive with volcanic activity producing vast quantities of carbon dioxide. Being a powerful greenhouse gas, carbon dioxide helped warm the atmosphere of both planets. In fact, without any greenhouse effect, Earth’s surface temperature would be an estimated -18°C instead of its present-day 16°C.

Mars, due to a combination of no longer having any greenhouse effect and being some 41 million miles further away from the Sun than Earth, now has a mean surface temperature of -63°C. Nonetheless, studies of the Allan Hills 84001 meteorite, which originated from Mars, have revealed that surface temperatures of 18±4°C were possible some 4 billion years ago when the meteorite crystallized from molten rock. Impressively, however, this is just one piece of evidence that suggests Mars was once much warmer, a characteristic that could only have been down to a thicker atmosphere and resultant greenhouse effect.

Last month, researchers concluded that heavy rain had played a major role in shaping the planet’s surface. As air pressures decreased from around 4 bars to 1.5 bars (Earth’s air pressure at sea level is 1 bar), raindrops could grow to larger sizes and fall faster, even despite the planet’s relatively low gravity. These larger and harder-falling raindrops cut into the Martian soil, forming surface features much like those found on Earth.

How Mars Lost Its Fight for Survival

Some 3.7 billion years ago, Mars started to undergo a profound transition that would forever redefine its surface and leave it the dead world we know today. Shortly after the Late Heavy Bombardment ended, volcanic activity on Mars increased, becoming the defining geological process of the planet’s surface. Olympus Mons, the largest volcano in the solar system, being some three times higher than Mount Everest, also formed during what is known as the Hesperian Period.

During the Early Hesperian, rampant volcanism created massive flows of magma, carving out vast canyons and volcanic plains. Although the climate was still warm, the increased volcanic activity saw Mars’s lakes and seas confined to smaller and smaller localized regions. At the same time, volcanic outgassing pumped the atmosphere full of sulphur dioxide and hydrogen sulphide, which would have made any remaining surface water extremely acidic, potentially killing off any microbial life that may once have thrived in it.

Sometime between 2.5 and 3.5 billion years ago, volcanic activity on Mars started to drop substantially. The planet became almost geologically dead, although there is strong evidence that isolated volcanic activity continued until relatively recently.

Mars’s magnetic field had long since withered and died too, leaving the planet unprotected from the solar wind. The loss of the magnetic field remains a mystery – it may have been down to impact events throwing the planet into chaos or simply because the planet isn’t massive enough to maintain a molten core and consequent dynamo effect for as long as Earth has. Either way, the loss of its magnetic field sometime during the first billion years of the planet’s history sealed its fate.

NASA

Geologically dead and void of any magnetic field, Mars had nothing to replenish and protect its atmosphere. Charged particles from the Sun, travelling at hundreds of miles per second, stripped it away over the aeons. Air pressures took a nose dive, as did surface temperatures, and any remaining water on the surface, already highly acidic, was permanently locked away in an icy tomb. At the same time, without a magnetic field or substantial atmosphere to guard it, the surface became dangerously irradiated by the Sun’s energy.

The solar wind continues to strip away what little is left of the atmosphere. Today, Mars is so inhospitable that a human explorer would survive for less than a minute without a spacesuit. The Red Planet is a mere shadow of its former self; a world that was once home to abundant water, a dense atmosphere and, perhaps, a living ecosystem like that of the ancient Earth.

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As we continue to explore Mars, we’re uncovering more and more fascinating insights into its distant past. Although there’s still no evidence of ancient life ever existing there, it seems far from impossible that life may have developed on the Red Planet, perhaps even earlier than it did on Earth. Do you think Martian life once existed or, perhaps, still does today? Let me know in the comments below!

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