An ancient northern ocean on Mars may have existed, according to a new set of topography maps. The maps present the most compelling evidence to date that the planet’s current harsh, frozen landscape is not what it once looked like and that sea levels rose in accordance with an extended period of warm, humid weather.
“What immediately comes to mind as one the most significant points here is that the existence of an ocean of this size means a higher potential for life,”
according to Benjamin Cardenas, lead author on the recently published study.
It also reveals information about the development of the ancient climate. These results indicate that there must have been a time when the temperature was high enough and the atmosphere was dense enough to support this much liquid water.
An Ancient Northern Mars Ocean
Cardenas says that scientists have been talking about whether or not Mars’s low-lying northern hemisphere has an ocean for a long time. Using topography data, the research team was able to show that a shoreline that was about 3.5 billion years old had a lot of sediment that was at least 900 meters thick and covered hundreds of thousands of square kilometers.
The new approach taken in this study was to consider Mars’ rock layering and sedimentary record.
“On Earth, we chart the history of waterways by looking at sediment that is deposited over time. We call that stratigraphy, the idea that water transports sediment and you can measure the changes on Earth by understanding the way that sediment piles up. That’s what we’ve done here — but it’s Mars.”
The group mapped data from the National Aeronautics and Space Administration (NASA) and the Mars Orbiter Laser Altimeter using software created by the United States Geological Survey. They found over 6,500 kilometres of fluvial ridges and organized them into 20 systems to demonstrate that the ridges are probably the remains of an ancient Martian shoreline that have been eroded into river deltas or submarine channel belts.
The team was able to understand how the paleogeography of the area changed over time by looking at things like the thicknesses, altitudes, positions, and possible sedimentary flow directions of rock formations. Cardenas noted that the area that was previously oceanic is now known as Aeolis Dorsa and features the densest collection of fluvial ridges on the globe.
“The rocks in Aeolis Dorsa capture some fascinating information about what the ocean was like. It was dynamic. The sea level rose significantly. Rocks were being deposited along its basins at a fast rate. There was a lot of change happening here,”
Cardenas explained that the stratigraphic records of Earth’s changing climate and life can be found in the old sedimentary basins. Stratigraphy is a field of geology that studies rock layers (strata) and layering (stratification). Its primary application is in the study of sedimentary and layered volcanic rocks.
Traces Of Habitable Life
If researchers want to find signs of life on Mars, which is one of the main goals of the Mars Curiosity rover missions, the best place to start would be an ocean the size of the one that used to cover Aeolis Dorsa.
“It’s always been looking for water, for traces of habitable life. This is the biggest one yet. It’s a giant body of water, fed by sediments coming from the highlands, presumably carrying nutrients. If there were tides on ancient Mars, they would have been here, gently bringing in and out water. This is exactly the type of place where ancient Martian life could have evolved,”
Cardenas and his associates have mapped what they believe to be additional prehistoric waterways on Mars. A study that will be published in the Journal of Sedimentary Research says that the Curiosity rover probably found sedimentary layers from ancient river bars at a number of outcrops.
In a different study, published in Nature Geoscience, a model of basin erosion akin to that on Mars is examined using the same acoustic imaging method that is used to see the stratigraphy beneath the seafloor of the Gulf of Mexico. According to the study, ancient river deposits eroded from vast basins similar to Aeolis Dorsa are likely the source of the fluvial ridge landforms, which are widely distributed across Mars’ topography.
“The stratigraphy that we’re interpreting here is quite similar to stratigraphy on Earth. Yes, it sounds like a big claim to say we’ve discovered records of large waterways on Mars, but in reality, this is relatively mundane stratigraphy. It’s textbook geology once you recognize it for what it is. The interesting part, of course, is it’s on Mars,”
Cardenas, B. T., & Lamb, M. P. (2022). Paleogeographic reconstructions of an ocean margin on Mars based on deltaic sedimentology at Aeolis Dorsa. Journal of Geophysical Research: Planets, 127, e2022JE007390.
Cardenas, B.T., Lamb, M.P. & Grotzinger, J.P. Martian landscapes of fluvial ridges carved from ancient sedimentary basin fill. Nat. Geosci. (2022).
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