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In May 2020, several unusual rocks containing distinctive greenish crystals were found in the Erg Chechen Sand Sea, a dune-filled region of the Sahara Desert in southern Algeria.
In May 2020, several unusual rocks containing distinctive greenish crystals were found in the Erg Chechen Sand Sea, a dune-filled region of the Sahara Desert in southern Algeria. On closer inspection, it turned out that the rocks came from outer space: billions of years old remnants from the beginning of the solar system.
These were all fragments of a meteorite known as Erg Chech 002, the oldest volcanic rock ever found, which melted long ago in the fires of some now-extinct ancient protoplanet.
In a new study published Nature Communication We analyzed the lead and uranium isotopes in Erg Chech 002 and estimated it to be about 4.56556 billion years old, plus or minus 120,000 years. This is one of the most accurate ages ever calculated for objects in space, and our results also challenge some common assumptions about the early Solar System.
About 4.567 billion years ago, our solar system consisted of a large cloud of gas and dust. Among the many elements in this cloud was aluminum, which exists in two forms. The first is aluminum-27, which is a stable form. The second is aluminum-26, a radioactive isotope produced primarily by exploding stars and decaying over time to magnesium-26.
Aluminum-26 is a very useful material for scientists who want to understand how the solar system formed and developed. Because it decays over time, we can use it specifically to date events within the first four or five million years of the Solar System’s life.
The degradation of aluminum-26 is also important for another reason: We believe it was the primary source of heat in the early solar system. This fragmentation affected the melting of tiny primordial rocks that later coalesced to form planets.
But to use aluminum-26 to understand the past, we need to know whether it is distributed evenly, or is it clustered more tightly in some places than others. To find out, we’ll need to calculate the absolute age of some ancient space rocks more precisely.
Looking at aluminum-26 alone, we won’t be able to do that because it decays relatively quickly (in about 705,000 years, half of a sample of aluminum-26 will decay into magnesium-26). This is useful for determining the relative age of different objects, but not for determining their absolute age in years.
But if we combine aluminum-26 data with uranium and lead data, we can make some progress. There are two important isotopes of uranium (uranium-235 and uranium-238) that decay into different isotopes of lead (lead-207 and lead-206, respectively). Uranium isotopes have much longer half-lives (710 million years and 4.47 billion years, respectively), which means we can use them to directly determine how long ago an event occurred.
Erg Chech 002 is what is known as “ungrouped achondrite”.
Achondrites are rocks made up of molten planetary material, which we call solid lumps in the cloud of gas and debris that make up the Solar System. The source of many achondrites found on Earth has been determined.
Most belong to the Howardit-Eukrit-Diogenit clan, believed to have descended from Vesta 4, one of the largest asteroids in the Solar System. Another group of achondrites is called angrits, and they all have an unidentified main body. Other achondrites, including Erg Chech 002, are “ungrouped”; parental bodies and family relationships are unknown.
In our study of Erg Chech 002, we found that it contains large amounts of lead-206 and lead-207, as well as relatively large amounts of degraded uranium-238 and uranium-235. Measuring the ratio of all isotopes of lead and uranium helped us estimate the age of the rock with unprecedented precision.
We also compared our calculated age with previously published aluminum-26 data for Erg Chech 002 as well as data for various other achondrites. Particularly interesting was the comparison with a group of achondrites called volcanic angrites. We found that the main body of Erg Chech 002 should have been composed of material containing three to four times more aluminum-26 than the source of the Angrite main body.
This suggests that aluminum-26 is indeed quite unevenly distributed in the cloud of dust and gas that makes up the solar system. Our results contribute to a better understanding of the early stages of the Solar System’s development and the geological history of the evolving planets. Further studies of the various achondrite groups will undoubtedly continue to improve our understanding and ability to reconstruct the early history of our solar system. Source
Source: Port Altele
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