How Is the Earth Formed? Deep Mantle Krypton Reveals the Answers

Krypton from the Earth's mantle reveals that small rock bodies from the icy outer solar system hit the Earth millions of years before the big crunch. The samples also showed that the young Earth was hit by meteorites and sucked up dust and gas from the solar nebula (the cloud that surrounds the sun).

According to the University of California, Davis, the current discovery challenges the widely held belief that the majority of Earth's volatile elements were delivered near the conclusion of the planet's development, which is characterized by the moon-forming big impact.

"Our results require concurrent delivery of volatiles from multiple sources very early in Earth's formation," said study lead author Sandrine Péron in a statement. Péron conducted the research as a postdoctoral scholar at UC Davis. She collaborated with Professor Sujoy Mukhopadhyay of the Earth and Planetary Sciences Department. Researchers detailed their study, "Deep-Mantle Krypton Reveals Earth's Early Accretion of Carbonaceous Matter," in the journal Nature.

Krypton Unveils Earth's Outer Solar System Ancestry

Phys.org said the chemical fingerprint of deep mantle krypton was determined to be very similar to that of primordial, carbon-rich meteorites, which may have been brought from the frigid, far reaches of the solar system. However, Mukhopadhyay and colleagues previously discovered that neon, another noble gas found in the deep mantle, was produced from the sun. The two findings point to at least two unique volatile sources for the Earth's mantle, both given early in the planet's history. In comparison to known meteorites, the researchers found less of the uncommon isotope Kr-86 in the deep mantle. The lack of Kr-86 shows that available meteorites may not account for all of the Krypton in the mantle.

The new findings also have ramifications for the formation of Earth's atmosphere. The researchers discovered that the ratio of distinct krypton isotopes in the deep mantle did not match the isotope ratio in Earth's atmosphere. It suggests that certain gases in the atmosphere, including noble gases like Krypton, were transferred to Earth following the moon-forming collision. Otherwise, due to isotopic equilibration following the impact, the Earth's mantle and atmosphere would have the same isotopic makeup, according to Péron.

Old Geochemistry

Slushy magma plumes rising from the lowest mantle layer feed the volcanic hot spots pouring lava in Iceland and the Galapagos, Eurekalert said. The metals and minerals in this deep layer have remained mostly intact since the moon-forming collision, serving as a time capsule of the early Earth's chemistry dating back over 4.4 billion years.

Mukhopadhyay's laboratory specializes in measuring noble gases in rocks from all over the world. The team retrieved lava from hot spot plumes to investigate deep mantle krypton. When the lava cools to a solid, the old gases rise to the top and get imprisoned and entombed as bubbles in a glassy matrix, offering some protection from outside pollution. However, even the most prevalent krypton isotopes in these bubbles only amount to a few hundred million atoms, making identification difficult, according to Mukhopadhyay.

Péron devised a novel mass spectrometry technique for detecting mantle krypton, concentrating Krypton from rock samples in an almost air-free atmosphere and cleanly separating it from argon and xenon.

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