The Secret Life of Aluminum and the Age of Erg Chech 002 Meteorite

Friday - September 8 2023, 19:24 UTC - 1 year ago

Algerian scientists discovered the oldest meteorite fragments from space, Erg Chech 002, using a combination of aluminum-26, uranium, and lead data to determine its age. These sketchy fragments and the isotopy research of along with it could reshape assumptions about the very beginnings of the solar system.

In May 2020, some unusual rocks containing distinctive greenish crystals were found in the Erg Chech sand sea, a dune-filled region of the Sahara Desert in southern Algeria. On close inspection, the rocks turned out to be from outer space: lumps of rubble billions of years old, left over from the dawn of the solar system. They were all pieces of a meteorite known as Erg Chech 002, which is the oldest volcanic rock ever found, having melted long ago in the fires of some now-vanished ancient protoplanet. In new research published in Nature Communications, we analyzed lead and uranium isotopes in Erg Chech 002 and calculated it is some 4.56556 billion years old, give or take 120,000 years. This is one of the most precise ages ever calculated for an object from space—and our results also cast doubt on some common assumptions about the early solar system.

The Secret Life of Aluminum .

Around 4.567 billion years ago, our solar system formed from a vast cloud of gas and dust. Among the many elements in this cloud was aluminum, which came in two forms. First is the stable form, aluminum-27. Second is aluminum-26, a radioactive isotope mainly produced by exploding stars, which decays over time into magnesium-26. Aluminum-26 is very useful stuff for scientists who want to understand how the solar system formed and developed. Because it decays over time, we can use it to date events—particularly within the first four or five million years of the solar system’s life.

The decay of aluminum-26 is also important for another reason: we think it was the main source of heat in the early solar system. This decay influenced the melting of the small, primitive rocks that later clumped together to form the planets.

Uranium, Lead, and Age .

However, to use aluminum-26 to understand the past, we need to know whether it was spread around evenly or clumped together more densely in some places than in others. To figure that out, we will need to calculate the absolute ages of some ancient space rocks more precisely. Looking at aluminum-26 alone won’t let us do that, because it decays relatively quickly (after around 705,000 years, half of a sample of aluminum-26 will have decayed into magnesium-26). It’s useful for determining the relative ages of different objects, but not their absolute age in years.

But if we combine aluminum-26 data with data about uranium and lead, we can make some headway. There are two important isotopes of uranium (uranium-235 and uranium-238), which decay into different isotopes of lead (lead-207 and lead-206, respectively). The uranium isotopes have much longer half-lives (710 million years and 4.47 billion years, respectively), which means we can use them to directly figure out how long ago an event happened.

Meteorite Groups .

Erg Chech 002 is what is known as an "ungrouped achondrite." Achondrites are rocks formed from melted planetesimals, which is what we call solid lumps in the cloud of gas and debris that formed the solar system. The sources of many achondrites found on Earth have been identified. Most belong to the so-called Howardite-Eucrite-Diogenite clan, which are believed to have originated fro the asteroid Vesta and were later flung out into interplanetary space by impacts.