When did water appear on Earth?

Looking back over the origins of our world billions of years ago, we see how celestial bodies began to form in the giant, spinning disk of dust, gas, and rocky debris that swirled around our Sun. This amazing process, known as accretion, gradually led to the planets, moons, and asteroids that inhabit our cosmic landscape. To this day, however, scientists continue to explore and struggle to understand the complex processes that led to the birth of planet Earth.

The study of magma, the molten or semi-molten natural rock that emerges from deep within the Earth’s core, is one of the primary methods researchers use to understand the formation of the Earth. Magma samples contain chemical signatures that chronicle our planet’s birth, detailing the timing and nature of the constituent materials that contributed to Earth’s formation. This is similar to how fossils give us clues about Earth’s biological past.

A recent study by the California Institute of Technology reveals a new chapter in the story of our planet’s creation. Researchers François Tissot and Yigang Zhang of the University of the Chinese Academy of Sciences, along with graduate student Wei Liu of the California Institute of Technology, conducted a groundbreaking study published in Science Advances. Their work shows that the early Earth was created from hot and parched materials, and that water appeared relatively late in the planet’s formation history.

Magma samples from Earth’s mantle, which break through to the surface in volcanic eruptions, play an important role in the study of Earth’s formation. Although humans have not yet figured out a way to physically penetrate into the heart of our planet, rocks deep in the Earth’s mantle can reach the surface, bringing important samples with them.

By analyzing magmas of varying depths, scientists can gain information about the distinct chemical composition of Earth’s layers. The formation of the Earth was a long process in which materials gradually came together over an enormous period of time. During the study, a team of scientists discovered that the early Earth was mostly composed of dried rocky substances. This discovery points to the absence of volatile substances such as water and iodine in the early Earth. Samples of the upper mantle contained a higher proportion of volatiles, three times more than those in the lower mantle.

Wei Liu developed a model based on these chemical ratios that shows that the Earth originally formed from arid, rocky materials, and a significant infusion of volatiles necessary for life occurred during the last 15 percent of Earth’s formation.

This discovery changes our view of the origin and development of the Earth. Previously, we believed that water was present on Earth from the very beginning of its formation. But new research shows that water appeared relatively late in the planet’s history. This opens up new possibilities for studying the processes that led to the emergence of life on Earth.

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