Meteorite Preserves Chunks of Mars' Earliest Crust: Rock Could Reveal What the Red Planet's Environment Was like Billions of Years Ago
Grant, Andrew, Science News
Pieces of Mars' original crust have shown up in fragments of a smooth black rock recovered in the Sahara Desert, researchers report in the Nov. 28 Nature. The meteorite pieces are among the oldest planetary artifacts ever discovered and could provide insight into surface conditions on Mars during its infancy.
Along with the other planets in the solar system, Mars formed more than 4.4 billion years ago. But you'd never know that by studying meteorites that got blasted off the Red Planet before crash-landing on Earth. Most of the roughly 125 Martian meteorites on record formed less than a billion years ago, providing clues to recent geological activity on Mars but not what it looked like in its youth. The only senior citizen in the Martian collection is Allan Hills 84001, the 4.1-billion-year-old meteorite best known for the discredited claim that it contains fossilized bacteria (SN: 5/8/10, p. 10).
Carl Agee, a meteorite researcher at the University of New Mexico in Albuquerque, knew he had something special when a collector gave him samples of a glassy dark stone, nicknamed Black Beauty by a Moroccan dealer who sold it for $50 per gram. In February, Agee and his colleagues reported that they used a traditional method of dating, measuring the ratio of rubidium to strontium, to estimate the rock's age at 2.1 billion years (SN: 1/26/13, p. 10).
Munir Humayun, a Florida State University geochemist who received a sample from a different collector, decided to dig a bit deeper. He saw that the rock contains small crystals called zircons that form when magma solidifies. He and his team probed five zircons using a technique that measures how much of a particular uranium isotope has radioactively decayed into lead.
Humayun and colleagues now report that the crystals yielded an age of 4.4 billion years, making the crystals a remnant of the very first Martian crust. …