New theory links ancient Martian oceans with volcanic eruptions

Eruptions of Tharsis could have warmed the planet, enabling liquid water to exist on its surface.
By Laurel Kornfeld | May 22, 2018
A new theory proposed by researchers at the University of California, Berkeley (UC Berkeley), links the presence of an ancient ocean that existed on the Martian surface four billion years ago with eruptions of the planet's largest volcano, known as Tharsis.

According to this theory, ancient Martian oceans formed either before or at the same time as Tharsis, which is known to be 3.7 billion years old.

Gases spewed into the atmosphere when Tharsis erupted warmed the planet through a greenhouse effect, raising temperatures to those in which liquid water can exist on a planet's surface.

The eruptions also formed channels through which subsurface water traveled to the surface, creating an ocean in Mars's northern plains.

Tharsis was significantly smaller then than it is now, specifically not large enough to deform Mars's crust as it does today. Without a deformed crust, the ancient ocean would have been significantly more shallow than previously thought.

Scientists believe the ancient seabed was located in the plains covering most of Mars's northern hemisphere.

"Volcanoes may be important in creating the conditions for Mars to be wet," said Michael Manga of UC Berkeley, and lead author of a paper on the theory published in the journal Nature.

One argument used by those who claim Mars never had a liquid ocean on its surface is that its polar ice caps do not contain sufficient water for an entire ocean, even taking into account the water that eventually escaped into space.

"The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later," Manga noted. "We're saying that the oceans predate and accompany the lava outpourings that made Tharsis."

This theory could also explain the irregular shorelines on Mars, the researchers believe. If Mars's first ocean started forming four billion years ago, the volcano, growing at the same time, could have deformed the shorelines.

"These shorelines could have been emplaced by a large body of liquid water that existed before and during the emplacement of Tharsis, instead of afterwards," emphasized study first author Robert Citron, also of UC Berkeley.

With a diameter of 5,000 miles, Tharsis contains some of the solar system's largest volcanoes and dominates the landscape of Mars's northern hemisphere, creating a bulk on the planet's opposite side.

To either prove or disprove the theory, scientists will need to more accurately pin down Tharsis's exact age.

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