Crystal-studded space rocks found in the desert may rewrite the history of the early solar system
In May 2020, some unusual rocks containing distinctive green crystals were found in the Erg El-Shih sand sea, a dune-strewn area in the Sahara Desert in southern Algeria.
On closer inspection, the rocks turned out to be from outer space: lumps of rubble It is billions of years oldremaining from the dawn of the solar system.
They were all pieces of a meteorite known as Erg Chech 002, the oldest igneous rock ever found, long ago melted in the fires of some now-vanished ancient protoplanet.
in New search Published in the journal Nature Communications, we analyzed lead and uranium isotopes in Erg Chech 002 and calculated that it is about 4.56556 billion years old, or minus 120,000 years. This is one of the most accurate ages ever calculated for an object from space, and our results cast doubt on some common assumptions about the early solar system.
Related: The world’s first “bouncing meteorite” – a rock that left Earth, spent thousands of years in space and then returned – may have been discovered in the Sahara Desert
The Secret Life of Aluminum
About 4.567 billion years ago, our solar system formed from a huge cloud of gas and dust. Among the many elements in this cloud was aluminium, which came in two forms.
The first is the stable form, which is aluminum-27. The second is aluminum-26, a radioactive isotope produced mainly by exploding stars, which decays over time to magnesium-26.
Aluminum-26 is a very useful material for scientists who want to understand how the solar system formed and evolved. Because it decays over time, we can use it to date events, especially during 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 affected the melting of primitive small rocks that later aggregated to form planets.
Uranium, lead and age
However, to use aluminum-26 to understand the past, we need to know whether it was more evenly spread or clustered together more densely in some places than in others.
To find out, we’ll need to more accurately calculate the absolute ages of some ancient space rocks.
Looking at aluminum-26 alone would not allow us to do this, because it decays relatively quickly (after about 705,000 years, half a sample of aluminum-26 will decay to magnesium-26). It is useful to determine the relative ages of different objects, but not their absolute age in years.
But if we combine the aluminum-26 data with data on uranium and lead, we can make some progress.
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).
Uranium isotopes have much longer half-lives (710 million years and 4.47 billion years, respectively), which means we can use them to directly find out how long it has been since an event occurred.
meteorite groups
Erg Chech 002 is what is known as an “unassembled chondrite”.
Achondrites are rocks formed from molten planetesimals, what we call solid clumps in the cloud of gas and debris that formed the solar system. Many of the chondrites found on Earth have been sourced.
Most of them belong to the so-called Howardite-Eucrite-Diogenite clan, which is thought to have originated from Vesta 4, one of the largest asteroids in the solar system. Another group of chondrites is called anchorites, which all share an unknown parental body.
Other chondrites, including Erg Chech 002, remain “ungrouped”: their parent bodies and familial relationships are unknown.
Lumpy spread of aluminum
In our study of Erg Chech 002, we found that it contains high abundances of lead 206 and lead 207, as well as relatively large amounts of undecomposed uranium 238 and uranium 235.
Measuring the proportions of all isotopes of lead and uranium was what helped us estimate the age of the rock with this unprecedented accuracy.
We also compared our calculated ages with previously published aluminum 26 data for Erg Chech 002, as well as data for various other chondrites.
The comparison with a group of achondrites called volcanic angerite was particularly interesting. We found that the original body of Erg Chech 002 must have been formed from a material containing three or four times the amount of aluminum 26 as the original body source of the angrits.
This indicates that aluminum-26 was unevenly distributed throughout the cloud of dust and gas that formed the solar system.
Our results contribute to a better understanding of the early developmental stages of the solar system and the geological history of nascent planets. Undoubtedly, additional studies of diverse achondrite groups will continue to improve our understanding and enhance our ability to reconstruct the early history of our solar system.
This edited article is republished from Conversation Under Creative Commons Licence. Read the The original article.
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