Early Mars Was Covered with Ice Sheets, Not Flowing Rivers - Science Reveals
Mars may once have been covered by ice sheets that were not covered by rivers, new research published Monday in Nature Geoscience shows. Most of Mars “valleys are formed by ice sheets — not rivers — which calls into question the planet’s supposedly warm, watery past and potential for life.
According to a new UBC study published today in Nature Geoscience, many of the valley networks that scarred the surface of Mars were excavated by free-flowing rivers, not ice sheets as previously thought, according to a new analysis of data from NASA’s Mars Reconnaissance Orbiter (MRO) published August 3 in Nature Geosciences. In fact, the large number of valley networks drawn by the Martian surface may have been dug into them by rivers in the past, making the planet’s surface much warmer than it is today, as a recent analysis by the University of BC in today’s natural geoscience shows. According to the new study by the University of British Columbia, published in today’s Science, free-flowing rivers — like networks on Mars — were carved out of the ground not by ice sheet ice, but into a valley system the size of the largest number they have carved into the surface of Mars.
In early August 2020, Mars researchers announced that many of these channels were formed not by flowing river water at all, but by erosion, suggesting that rivers and lakes on early Mars were less abundant than previously thought. In Nature Geoscience, Grau-Galofre and two colleagues report that much of the water that has formed on the Martian surface comes not from ice sheets, but from rivers, lakes, and other water sources. The researchers also found that valleys that looked like they had been formed by meltwater from glaciers were spread over a wide area, while the valleys that appeared to have been formed by rivers were concentrated in a few areas, such as the northern and southern parts of Mars “southern polar regions. They compared the valleys and the shape of erosion — cut valleys on Mars — with the shapes of valleys carved out of erosion by glaciers on Earth, as well as the size of their valleys.
If the researchers are right, their conclusions appear to literally whitewash the question of whether Mars was warm and humid enough to flood rivers and rain oceans early on. Instead, the scientists say, these channels are the result of ice sheets from the Ice Age that crawled across the Martian surface long ago. Given what scientists know about early Mars, there is some evidence that there are rivers on the planet’s early surface. If many of Mars “rivers are actually formed by melting ice and not flowing surface water, this would be further proof of how much water Mars had in the past and how habitable the planets were a few billion years ago, Grau-Galofre and his colleagues say.
But Galofre is not convinced that surface rivers flowed freely on a warm, moist Mars. The lack of evidence of rivers on early Mars and the lack of water on the planet’s surface have led some to believe that Mars was never warm and wet, but a largely frozen planet covered by ice sheets and glaciers.
This has led to the assumption that Mars was very Earth-like — with flowing rivers dug into valleys, canals, and scars on its surface. Some researchers believe there is no evidence of how many river valleys on Mars have been excavated, or even free-flowing rivers on the planet.
Previous interpretations of geological records require precipitation and surface water to form valley networks, while climate simulations predicted a cold, icy ancient Mars. Old Mars, the new research suggests, was a temperate, moist planet, which is often thought to have been warmer and wetter in the past. Mars has many dry river valleys, and this conclusion is consistent with the fact that the planet has been warm and dry in its past, according to a new study by scientists at the University of California, Berkeley.
When glaciers retreated during intermittent warm periods, rivers flowed, severed channels of varying shapes in the ice sheets, and then flowed back into the ocean. The formation of these river valleys and other river systems is known in geological history, but is associated with extremely large ice sheets.
According to the scientists, this type of erosion creates valleys similar to those of surface water that flows freely. Many studies of Martian valleys interpret them as the result of free-flowing rivers, not ice sheets. However, the new study makes clear that most of these valleys were actually created by the river itself. There seem to be many Martian valleys that scientists are studying that are the product of ice sheet erosion rather than free flow from the surface.
Researchers from the University of British Columbia say free-flowing rivers, notice sheets, have crisscrossed the valley networks guarding the surface of Mars. The study challenges the widely held view that most valley networks on Mars are formed by rivers that feed on rainfall. This research provides the first direct evidence of the existence of rivers — such as valleys in the early Martian environment.
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