Study paves way for new theories about how Earth got its iron

New research suggests Earth's excess of heavy iron isotopes could have developed as a result of a violent collision between Earth and another planetary body. Photo by NASA/Caltech

March 21 (UPI) — Most scientists believe the formation of Earth’s core explains the planet’s unique levels of heavier iron isotopes, iron atoms with larger numbers of neutrons in their nuclei. But a new study challenges the theory, paving the way for alternative explanations.

Scientists found the ratio of iron isotope Fe-56 to the lighter Fe-54 is identical in moon, Mars and ancient meteorite samples. Earth, however, features a higher concentration of heavy iron isotopes.

Traditionally, Earth’s core explained the discrepancy. But researchers at the University of Chicago and University of Texas at Austin believe Earth’s unique iron isotopic ratio emerged later in Earth’s history. Scientists suggest a violent collision between Earth and another planetary body may have vaporized lighter iron isotopes.

“The Earth’s core formation was probably the biggest event affecting the Earth’s history,” Jung-Fu Lin, professor of geosciences at Austin, said in a news release. “In this study we say that there must be other origins than the Earth’s formation for this iron isotopic anomaly.”

Researchers used a diamond anvil cell to recreate the intense pressures experienced by atoms during the formation of Earth’s core. The diamond anvil cell allowed scientists to observe various chemical reactions under extreme conditions.

“The diamond anvil cell has been used in this way before, but the difficulty is getting correct numbers,” said Nicolas Dauphas, a professor of geophysical sciences at Chicago. “That requires great care in data acquisition and treatment because the signal the diamond anvil gives off is very small. One has to use sophisticated mathematical techniques to make sense of the measurements, and it took a dream team to pull this off.”

Their experiments showed core formation reactions failed to produce an excess of heavy iron isotopes or destroy lighter iron isotopes.

Researchers expect their findings — detailed in the journal Nature Communications — to force geophysicists and planetary scientists back to the drawing board. Earth’s core can’t explain its unique iron isotopic ratio.

“The solution to this mystery must be sought elsewhere,” Dauphas said.


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