Scientists have analyzed 3.7-billion-year-old rocks from Western Australia to uncover details about the early Earth and the Moon's origins. The study indicates that Earth's continents began forming around 3.5 billion years ago, long after the planet itself emerged. Comparisons with Apollo mission samples support the theory of a massive cosmic collision birthing the Moon.
In a new study published in Nature Communications, researchers led by PhD student Matilda Boyce from the University of Western Australia examined tiny feldspar crystals within anorthosites collected from the Murchison region. These rocks, dating back 3.7 billion years, are among the oldest known on the Australian continent and provide a preserved record of Earth's ancient mantle.
"The timing and rate of early crustal growth on Earth remains contentious due to the scarcity of very ancient rocks," Boyce noted. Using high-precision isotopic analysis on untouched parts of plagioclase feldspar crystals, the team found that significant continental growth did not start until approximately 3.5 billion years ago—about one billion years after Earth's formation around 4.5 billion years ago. This delay challenges previous assumptions about the rapid development of the planet's crust.
The findings also connect Earth's history to the Moon's. By comparing the Australian samples with lunar anorthosites returned by NASA's Apollo missions, the researchers observed a striking chemical similarity. "Anorthosites are rare rocks on Earth but very common on the Moon," Boyce explained. "Our comparison was consistent with the Earth and Moon having the same starting composition of around 4.5 billion years ago. This supports the theory that a planet collided with early Earth and the high-energy impact resulted in the formation of the Moon."
The research involved collaborators from the University of Bristol, the Geological Survey of Western Australia, and Curtin University, with funding from the Australian Research Council. These insights offer a clearer timeline for planetary evolution, highlighting how a catastrophic event shaped both worlds.
