How old are Martian meteorites?
Most Martian meteorites crystallised between about 150 million and 1.4 billion years ago, but a few are much older, up to about 4.4 billion years.
Martian meteorites have a wide range of ages, and their youth compared with most meteorites was one of the clues that they came from Mars.
Shergottites, the most common Martian meteorites, are mostly young. Many crystallised between about 150 and 600 million years ago, with a few older ones around 2.4 billion years. This shows that volcanoes on Mars were active relatively recently in geological terms.
Nakhlites and chassignites crystallised about 1.3 to 1.4 billion years ago. They seem to come from the same volcanic region, perhaps the same lava flow or intrusion, and were launched from Mars together.
ALH 84001, an orthopyroxenite found in Antarctica, crystallised about 4.1 billion years ago. It is one of the oldest Martian rocks known.
NWA 7034 and its pairs, nicknamed Black Beauty, is a regolith breccia containing fragments, especially zircon crystals, as old as about 4.4 to 4.5 billion years, showing that Mars had a crust very early.
Scientists also measure ejection ages: how long ago the rocks left Mars, based on cosmic-ray exposure. Most Martian meteorites were ejected within the last 20 million years, in perhaps ten or so separate impact events. Nakhlites and chassignites, for example, were ejected about 11 million years ago.
The young ages of most Martian meteorites present a puzzle, because much of Mars's surface is ancient. It may be that young, strong volcanic rocks are better at surviving ejection, or that the craters producing them happened to be in young terrains.