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Oct 23rd 2018

Africa Yields Clues to the Formation of Mars

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If you were a geologist searching for evidence about the formation of Mars, you might think that you would have to travel to Mars to look for it. But some critical new Mars discoveries have come from an unexpected place — the Sahara Desert.

The evidence, reported by Space.com, came in the form of a meteorite found in 2011 in Northwest Africa, appropriately named Northwest Africa (NWA) 7034. Dubbed “Black Beauty,” the meteorite was at first taken for an ordinary earthly rock.

It sat for months on one scientist’s shelf before close examination showed that it was indeed a meteorite, according to Science.

Through Zircons, a Window Into Deep Time

NWA 7034’s chemical composition showed that it originated on Mars — yet it differed from other meteorites known to be of Martian origin, said Science.com.

A rock’s composition and structure tell the story of its history; for NWA 7034, this means an extraordinary history stretching back 4.547 billion years to a time when, per Space.com, the entire solar system was only about 20 million years old.

The meteorite contains crystals known as zircons, which contain naturally radioactive uranium and hafnium atoms. The gradual radioactive decay of these atoms allows precise measurement of the time that has passed since a zircon formed. This trait leads one researcher to describe a zircon, according to Space.com, as “‘a small time capsule'”

Analysis of seven zircons from NWA 7034 shows that they formed between 4.43 and 4.48 billion years ago; one zircon is the oldest piece of Mars measured so far. But measurement of hafnium in the zircons showed that it had been encased in solid rock for some 100 million years before cataclysmic ancient forces transformed the original rock and formed the zircons themselves, said Space.com.

A Journey Through Space and Time

The halfnium measurements show that Mars took form rapidly by cosmic standards. By the time the solar system was 20 million years old, the formation of Mars had already proceeded far enough to form a solid rocky crust — a necessary precondition for water vapor in the atmosphere to condense into oceans as the planet gradually cooled, according to Space.com.

By comparison, the solidification of Earth’s crust, noted Space.com, took about 130 million years longer. Mars may have had a substantial head start over Earth in forming oceans and, potentially, providing an environment in which life could emerge. We don’t know when oceans actually formed on Mars — only that they did. We can still identify seabeds and riverbeds, all now cold and dry.

The History of Mars and “Black Beauty”

The early history of Mars had its share of dramatic events. According to Lawrence Livermore National Laboratory, a probable enormous impact “repaved” much of the surface a hundred million years after it solidified — it was the forces of this impact that created the zircons in NWA 7034.

The Lawrence Livermore account also noted that between 1.3 and 1.7 billion years ago, volcanic eruptions reshaped the surface from which NWA 7034 later came. Later still, according to Science, came another massive impact on Mars that knocked “Black Beauty” into space, where it finally collided with Earth and ended up in the Sahara Desert a few thousand years ago.

Meanwhile, reported Space.com, Mars lost its oceans, beginning some 4 billion years ago when its planetary magnetic field weakened to the point where it could no longer protect the Martian atmosphere from solar radiation storms. Mars became cold and dry.

But all of the water was not lost. As National Geographic noted, other recent Mars discoveries suggest that at least one underground lake still exists on Mars. And where there is liquid water, there might be life.

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