Scientists have analyzed one of the oldest space rocks ever discovered. Erg Chech 002 meteorite, encrusted with green crystals, was found in the Sahara Desert and is approximately 4.6 billion years old. The data could reveal the secrets of the early Solar System during the birth of planets.
Early Solar System
Meteorites like this one are believed to have formed from the material within the gas and dust disk around the newly born Sun. Cold and dense regions of this “solar nebula” collapsed to give birth to planets. The excess material, on the other hand, led to the formation of comets and asteroids. Consequently, meteorites can paint a picture of the building blocks of planets.
Erg Chech 002 meteorite contained the radioactive isotope Aluminum-26 4.6 billion years ago. This unstable form of aluminum is believed to have been important in a later stage of Earth’s evolution. According to the team led by Evgenii Krestianinov, this is known as “planetary differentiation” as illustrated in an article published in Nature Communications (rif.).
Planetary differentiation is the process by which rocky planets like ours form different compositions in different layers. This is because differentiation allows denser material to sink into the planet’s core. So, for Earth, an example of this differentiation would be the formation of a dense metallic core and, above it, a less dense rocky mantle.
Aluminum-26’s decay
Understanding the distribution of aluminum-26 during planet formation is important to grasp how rocky planets evolved. Additionally, since aluminum-26 decays into stable magnesium-26, it can be used as a dating system for space rocks.
To determine the age of Erg Chech 002, which is 4.566 billion years old, the team measured the quantity of lead isotopes within it. “Aluminum-26 is very useful material for scientists looking to understand how the solar system formed and developed,” said Krestianinov. “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 half-life of aluminum-26 is about 717,000 years. This time is too short to be found directly in large quantities in space rock. But when it decays, this radioactive isotope leaves behind stable, non-radioactive magnesium-26. So, magnesium-26 can be used to determine the initial amount of aluminum-26. That’s why it could be used as a dating system for meteorites.
Is this dating method correct?
“The Aluminum-26 – Magnesium-26 decay system also serves as a high-resolution relative chronometer”, the authors write. They add that it’s important to determine how aluminum-26 was distributed in the solar nebula. The 4.6-billion-year-old meteorite is an achondritic rock formed from the fusion of planetesimals. Comparing it with angrite meteorites, a rare group of achondrites that have characteristics similar to volcanic rock here on Earth.
“We found that the original body of Erg Chech 002 must have formed from material containing three or four times the amount of aluminum-26” Krestianinov stated. “This shows that aluminum-26 was indeed distributed rather unevenly in the dust and gas cloud that formed the Solar System”.
This discovery reevaluates the presence of Aluminum-26 in the early Solar System. It also suggests that the age of meteorites dated using only this method should be revised. “The development of a generalized approach to isotopic dating with aluminum-26, magnesium-26, and other extinct isotopic chronometers would allow us to produce more accurate data. The heterogeneous distribution of the parent radionuclide must be considered for reliable estimates” the authors concluded.