The Earth Formed Much Faster Than Previously Thought

They may not look like much, but CI chondrites — small fragile meteorites as shown here — are thought to be our best compositional equivalents of the bulk material of our solar system.  (Image: StarPlan, Globe Institute, University of Copenhagen)
They may not look like much, but CI chondrites — small fragile meteorites as shown here — are thought to be our best compositional equivalents of the bulk material of our solar system. (Image: StarPlan, Globe Institute, University of Copenhagen)

The precursor of our planet, the proto-Earth, formed within a time span of approximately 5 million years, shows a new study from the Centre for Star and Planet Formation (StarPlan) at the Globe Institute at the University of Copenhagen. On an astronomical scale, this is extremely fast, the researchers explain. If you compare the solar system’s estimated 4.6 billion years of existence with a 24-hour period, the new results indicate that the proto-Earth formed in what corresponds to about a minute and a half.

A small vial with the fragile meteorite-type CI chondrite. (Image: StarPlan, Globe Institute, University of Copenhagen)

A small vial with the fragile meteorite-type CI chondrite. (Image: StarPlan, Globe Institute, University of Copenhagen)

Thus, the results from StarPlan break with the traditional theory that the proto-Earth formed by random collisions between larger and larger planetary bodies throughout several tens of millions of years — equivalent to about 5-15 minutes out of the above-mentioned fictional 24 hours of formation. Instead, the new results support a more recent, alternative theory about the formation of planets through the accretion of cosmic dust. The study’s lead author, Associate Professor Martin Schiller, explains:

The bulk composition of the Solar System

The key to the new finding came in the form of the most precise measurements of iron isotopes that have so far been published scientifically. By studying the isotopic mixture of the metallic element in different meteorites, the researchers found only one type of meteoritic material with a composition similar to Earth: The so-called CI chondrites.

Associate Professor Martin Schiller. (Image: StarPlan, Globe Institute, University of Copenhagen)

Associate Professor Martin Schiller. (Image: StarPlan, Globe Institute, University of Copenhagen)

The researchers behind the study describe the dust in this fragile type of meteorite as our best equivalent to the bulk composition of the solar system itself. It was dust like this combined with gas that was funneled via a circumstellar accretion disk onto the growing Sun. This process lasted about 5 million years and our planets were made from material in this disk. Now, the researchers estimate that the proto-Earth’s ferrous core also formed already during this period, removing early accreted iron from the mantle.

Two different iron compositions

Other meteorites, for example from Mars, tell us that at the beginning the iron isotopic composition of material contributing to the growing Earth was different. Most likely due to the thermal processing of dust close to the young Sun, the researchers from StarPlan explain. After our solar system’s first few hundred thousands of years, it became cold enough for unprocessed CI dust from further out in the system to enter the accretion region of the proto-Earth. Martin Schiller explained:

More planets, more water, perhaps more life

Based on the evidence for the theory that planets form through the accretion of cosmic dust, the researchers believe that the same process may occur elsewhere in the universe. This means that other planets may also likely form much faster than if they grow solely from random collisions between objects in space.

Professor Martin Bizzarro from StarPlan presents different types of meteorites. (Image: StarPlan, Globe Institute, University of Copenhagen)

Professor Martin Bizzarro from StarPlan presents different types of meteorites. (Image: StarPlan, Globe Institute, University of Copenhagen)

This assumption is corroborated by the thousands of exoplanets — planets in other solar systems — that astronomers have discovered since the mid-nineties, explains Centre Leader and co-author of the study Professor Martin Bizzarro:

Bizzarro adds:

Provided by: University of Copenhagen [Note: Materials may be edited for content and length.]

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