Researchers examined 3.7‑billion‑year‑old plagioclase crystals from anorthosite in Western Australia to extract isotopic signatures of Earth’s early mantle and crust. Their data suggest major continental growth accelerated around 3.5 billion years ago, nearly a billion years after Earth formed. The isotopic fingerprints closely match Apollo lunar samples, lending support to the giant‑impact hypothesis that a Mars‑sized body struck proto‑Earth ~4.5 billion years ago and formed the moon. The study, led by the University of Western Australia, appears in Nature Communications.
Ancient Australian Rocks Offer New Evidence for the Moon’s Giant‑Impact Origin
Researchers examined 3.7‑billion‑year‑old plagioclase crystals from anorthosite in Western Australia to extract isotopic signatures of Earth’s early mantle and crust. Their data suggest major continental growth accelerated around 3.5 billion years ago, nearly a billion years after Earth formed. The isotopic fingerprints closely match Apollo lunar samples, lending support to the giant‑impact hypothesis that a Mars‑sized body struck proto‑Earth ~4.5 billion years ago and formed the moon. The study, led by the University of Western Australia, appears in Nature Communications.
02:38, 07.11.2025Science
Ancient Australian crystals preserve a record of Earth’s earliest chemistry
Some of Earth’s oldest surviving rocks, buried in Western Australia, may hold chemical clues about the dramatic event that formed the moon. In a new study led by the University of Western Australia (UWA), researchers analyzed 3.7‑billion‑year‑old plagioclase feldspar crystals from magmatic anorthosite in the Murchison region to recover isotopic "fingerprints" of Earth’s ancient mantle and crust.
Anorthosite forms when deep magmas cool very slowly, allowing large plagioclase crystals to grow and lock in geochemical information. Because these particular minerals have been unusually well preserved for some 3.7 billion years, the team was able to target fresh zones within the crystals using fine‑scale analytical techniques and measure isotopic ratios that record conditions in Earth’s formative years.
"The timing and rate of early crustal growth on Earth remains contentious due to the scarcity of very ancient rocks,"
said Matilda Boyce, the study's lead author and a Ph.D. student at UWA. "We used fine‑scale methods to isolate pristine zones of plagioclase that preserve ancient isotopic signatures."
The isotopic measurements indicate that large‑scale continental growth did not begin immediately after the planet formed. Instead, the results suggest significant continental crust formation accelerated around 3.5 billion years ago — nearly a billion years after Earth’s birth.
Perhaps most strikingly, the chemical signatures from the Australian anorthosites closely resemble isotopic patterns measured in lunar samples returned by NASA’s Apollo missions. That close match strengthens the leading giant impact hypothesis, in which a Mars‑sized body collided with the proto‑Earth about 4.5 billion years ago and ejected material that later coalesced into the moon.
"Our comparison was consistent with the Earth and moon having the same starting composition of around 4.5 billion years ago," Boyce said. "This supports the idea that a high‑energy impact produced the moon and left a shared chemical legacy in early terrestrial and lunar materials."
The work was carried out with collaborators at the University of Bristol, the Geological Survey of Western Australia and Curtin University, and was published Oct. 31 in Nature Communications. Because intact rocks from Earth’s infancy are extremely rare, the Murchison samples offer a valuable window into the planet’s early evolution and its link to the nascent moon.