So to untangle when conditions suitable for life may have arisen on Mars, we have to track the history of both water and impacts.
Martian meteorites are born when an impact on Mars ejects rocky fragments that later intercept Earth’s orbit.
The NWA 7034 meteorite, weighing about 320g, was found in the desert of northwest Africa and first reported in 2013.
Prior studies of NWA 7034 found it contains the oldest known zircons from Mars – some up to 4.48 billion years old.
It preserves microscopic damage caused by the passage of shock waves, and these “shocked grains” provide a solid record of impact.
With that in mind, we set out to survey additional zircon grains in NWA 7034 to see if we could find any that recorded evidence of impact.
This process can reorganise atoms within the crystal, to form a duplicated “twin” of zircon, which we can detect.
On Earth, shocked zircons with deformation twins are only found at impact craters.
Zircons with shock features have been found at Vredefort in South Africa, Sudbury in Canada and Chicxulub in Mexico.
Although determining the precise age of impact is difficult, geochemical studies of NWA 7034 reveal its main components were subject to meteorite impacts before roughly 4.3 billion years ago.
Alternatively, it may have formed more recently, but before a decline in the rate of impacts earlier than 3 billion years ago.
Our findings raise new questions about the early impact history of Mars.
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