The oldest volcanic meteorite challenges theories of the formation of the solar system

Analysis of the Erg Chech 002 meteorite has revealed that it is the oldest rock of volcanic origin ever found, far surpassing anything that originated on Earth. It also provided evidence that some parts of the early solar system were much richer than others in the isotopes responsible for most of their initial heat, although we still don’t know why.

The early Sun was not as bright as it is today, but that does not mean that the first planets to form from the surrounding disk were cold. Besides the heat released by impacts, radioactive isotopes were more abundant at the time, and kept the first large objects hot, often with molten interiors. One isotope in particular, aluminum-26, is thought to have played a particularly important role, and may be why plate tectonics exist today.

Today, the Earth’s core is heated mainly by the slow decay of uranium and thorium, and the same is true of the centers of other rocky bodies. However, four and a half billion years ago, aluminum-26 is thought to have played a much larger role.

Aluminum-26 decomposes into Mg-26, releasing energy along the way. At 705,000, its half-life is short enough for the heat to be more intense than similar amounts of uranium-235, but long enough to have a significant impact on the first few million years of planetary formation.

The protoplanetary disk from which the solar system formed was thought to have been rich in aluminum 26 from nearby exploding stars, but astronomers have debated whether the isotope was evenly mixed, or clustered in some areas. To test this, we need to know the exact timing of the meteorite formation. Otherwise, we can’t know whether one formed in a low-aluminum-26 region, or is a few million years younger, after most of the isotopes have decayed.

Volcanic meteorites are easier to date than those that have accumulated on the surface of an asteroid, so the discovery of Erg Chech 002 in the Sahara desert was a boon. Taking full advantage, Australian National University PhD student Evgeny Christianinov and co-authors have measured the age of Erg Chech 002 with astounding accuracy.

The volcanic origins of Erg Chech 002 mean that it originated in a body large enough to be geologically active. Some volcanic meteorites have been identified as coming from Vesta before falling in the impact. Others, including Erg Chech 002, apparently came from another object we cannot identify, likely because it was destroyed so long ago.

Erg Chech 002 is extraordinarily rich in lead and uranium, and this is no accident. Uranium undergoes a series of radioactive decay until it becomes a stable isotope of lead. When it was formed, the rock that later became Arg Shish 002 contained a greater amount of uranium, most of which had decayed into lead.

Different uranium isotopes decay at different rates, so by comparing the amounts of each and the proportions of their final products, geologists can calculate the age of rocks. Erg Chech 002 proved to be particularly suitable for giving accurate results: 4,565,560,000 years with an error of only 120,000 years.

By comparing the formation time of Erg Chech 002 with previous estimates of aluminum-26 concentration, Kristianinoff and co-authors concluded that its parent body must have contained three to four times the amount of aluminum-26 found in similar parent meteorites.

Unless the age or aluminum estimates are poor for one meteorite or another, this means that the cloud from which we formed was much less mixed than many had assumed.

This also means that during their merger, these protoplanets did not collect enough material from different regions to balance out these differences. This greatly complicates attempts to model planetary formation, but may also explain some anomalies.

Blinds 002 were For sale on eBay At very low prices, but now that their value has been established, they may rise fairly quickly.

The study is published in Nature Communications.