Was Mars’ past climate supportive of life?

The question of whether Mars ever supported life has fascinated scientists and the public for years. Central to this mystery is understanding the planet’s past climate: was it warm and wet, like Earth, or cold and icy, which would make it less hospitable to life? 

A new study suggests the latter, drawing parallels between Martian soils and those found in Newfoundland, Canada, a region with a cold subarctic climate.

Mars’ climate record in soil and rocks

Published on July 7th in Nature Communications: Earth and Environment, the study examined soils on Earth that contain materials similar to those in Mars’ Gale Crater. Scientists often use soil to uncover environmental history, as the minerals present can reveal landscape evolution over time. 

Understanding how these materials formed could answer long-standing questions about Mars’ ancient environment. The soils and rocks of Gale Crater offer a record of Mars’ climate from three to four billion years ago, a period when water was relatively abundant on the planet and life began on Earth.

“Gale Crater is a paleo lakebed – there was obviously water present. But what were the environmental conditions when the water was there?” said lead author Anthony Feldman, a soil scientist and geomorphologist at the Desert Research Institute in Las Vegas. 

“We’re never going to find a direct analog to the Martian surface, because conditions are so different between Mars and Earth. But we can look at trends under terrestrial conditions and use those to try to extrapolate to Martian questions.”

X-ray amorphous materials 

NASA’s Curiosity Rover has been exploring Gale Crater since 2011, uncovering various soil materials known as “X-ray amorphous material.” 

These materials lack the typical repeating atomic structure of minerals, making them difficult to characterize using traditional techniques like X-ray diffraction. 

The Curiosity Rover’s findings indicated that these amorphous materials made up between 15% and 73% of the soil and rock samples in the Gale Crater.

“You can think of X-Ray amorphous materials like Jello,” Feldman said. “It’s this soup of different elements and chemicals that just slide past each other.”

Limited chemical information 

The Curiosity Rover’s chemical analyses showed that these amorphous materials were rich in iron and silica but deficient in aluminum. 

Beyond this limited chemical information, scientists still don’t fully understand what these amorphous materials are or what their presence implies about Mars’ historical environment. Investigating how these materials form and persist on Earth could help answer these questions about Mars.

Soils on Earth with chemical similarities 

Feldman and his team searched for similar X-ray amorphous materials in Newfoundland’s Tablelands, Northern California’s Klamath Mountains, and western Nevada. 

These sites had serpentine soils expected to be chemically similar to those in the Gale Crater: rich in iron and silicon but lacking aluminum. 

The varying rainfall, snowfall, and temperature at these locations provided insight into the environmental conditions that produce and preserve amorphous materials.

Using X-ray diffraction analysis and transmission electron microscopy, the researchers found that the subarctic conditions in Newfoundland produced materials chemically similar to those in the Gale Crater, lacking crystalline structure. Soils from warmer climates like California and Nevada did not show these similarities.

“This shows that you need the water there in order to form these materials,” Feldman explained. “But it needs to be cold, near-freezing mean annual temperature conditions in order to preserve the amorphous material in the soils.”

Improved understanding of Mars’ past climate

Amorphous material is generally considered unstable because its atoms haven’t organized into a final, crystalline form. 

“There’s something going on in the kinetics – or the rate of reaction – that is slowing it down so that these materials can be preserved over geologic time scales,” Feldman explained. 

“What we’re suggesting is that very cold, close to freezing conditions, is one particular kinetic limiting factor that allows for these materials to form and be preserved.”

“This study improves our understanding of the climate of Mars. The results suggest that the abundance of this material in Gale Crater is consistent with subarctic conditions, similar to what we would see in, for instance, Iceland,” he concluded.

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