The Start of a Long Rain

~4 Billion Years Ago—The first occurrence of rainfall on Earth, according to recent research that examined oxygen isotopes in ancient minerals. Evidence taken from Australian hot springs had previously estimated Earth’s first rainfall as occurring about 3.5 billion years ago, but in the new study, a group of scientists used secondary-ion mass spectrometry to analyze oxygen isotopes in about 1,400 crystals of the mineral zircon taken from rocks in the Jack Hills in Western Australia. Zircon crystals from the Hadean geological period are the oldest surviving crustal material on Earth, and the crystals in the study dated as far back as 4.28 billion years ago. The researchers found some 4-billion-year-old zircon samples had extremely light isotopic signatures that would only be possible if they were exposed to meteoric water—that is, water that had recently fallen from the sky. “Such light oxygen isotopes are typically the result of hot, fresh water altering rocks several kilometers below Earth's surface,” explains the study’s lead author, Hamed Gamaleldien of Curtin University in Australia. The scientists ran tens of thousands of computer simulations and found that only when freshwater was added could they reproduce the light isotopic signature they found in their zircon. The findings, which were published in Nature Geoscience, "mark a significant step forward in our understanding of Earth's early history and open doors for further exploration into the origins of life," says coauthor Hugo Olierook, also of Curtin University. [Source: sciencealert.com]