Newswise — Billions of years back, within a vast disk of dust, gas, and rocky matter revolving around our youthful sun, masses grew and merged to create the celestial bodies we observe today: planets, moons, and asteroids. Scientists persist in unraveling the mechanisms behind the formation of planets, including our own abode. An approach employed by researchers involves scrutinizing the molten substances that ascend from the profound depths of Earth's core. Within the chemical imprints of these specimens lies a historical account of the materials' composition and the timeframe during which they amalgamated to shape our planet—similar to how fossils provide insights into Earth's biological past.
A recent Caltech study reveals that during the initial stages of Earth's formation, the accumulation process involved heated and arid materials. This finding suggests that the presence of water, a vital ingredient for the development of life, likely occurred at a later phase in the chronicles of our planet's creation.
Led by Francois Tissot, an assistant professor of geochemistry and Heritage Medical Research Institute Investigator, and Yigang Zhang from the University of Chinese Academy of Sciences, an international team of researchers carried out the study. The investigations took place in their respective laboratories. The findings of this research are detailed in a paper published in the journal Science Advances, with Weiyi Liu, a graduate student from Caltech, serving as the first author of the paper.
Although direct human exploration of Earth's interior remains beyond our reach, rocks from deep within the planet can emerge naturally in the form of volcanic lavas. These lavas originate from parental magmas, which can arise from various depths within Earth. For instance, the upper mantle begins approximately 15 kilometers beneath the surface and extends around 680 kilometers, while the lower mantle encompasses depths from 680 kilometers to the core-mantle boundary, roughly 2,900 kilometers below us. Analogous to sampling distinct layers of a cake—the frosting, the filling, the sponge—scientists can examine magmas originating from different depths to unravel the unique characteristics of Earth's various layers. This entails investigating the chemical composition of these magmas and their ratios relative to one another, providing insights into the diverse "flavors" present within Earth's structure.
As the formation of Earth unfolded gradually, with materials accumulating over time, samples obtained from the lower mantle and upper mantle provide distinct insights into the chronological progression of Earth's accretion. In the recent study, the research team made a significant discovery: the early Earth predominantly consisted of arid and rocky substances. Chemical signatures extracted from the planet's deep interior displayed a scarcity of volatile elements, such as water and iodine, which easily evaporate. In contrast, samples from the upper mantle exhibited a higher abundance of volatiles, approximately three times more than those found in the lower mantle. Drawing upon these chemical ratios, Liu developed a model that depicts Earth's formation from hot, dry, and rocky materials. Furthermore, the model suggests that a substantial influx of life-sustaining volatiles, including water, occurred only within the final 15 percent (or less) of Earth's formative period.
The study holds great significance in the realm of planet formation theories, an area that has witnessed numerous paradigm shifts in recent decades and continues to be the subject of lively scientific discourse. In this context, the findings of the new study offer valuable insights and predictions regarding the composition of the fundamental components of other terrestrial planets like Mercury and Venus. These planets, expected to have formed from comparable arid materials, can potentially provide further evidence to support the conclusions drawn from the study. The research thus contributes to our understanding of planetary formation processes and opens up avenues for further exploration and investigation.
According to Tissot, space exploration focusing on the outer planets holds tremendous significance due to the potential presence of water worlds, which are believed to offer optimal conditions for the search for extraterrestrial life. However, Tissot emphasizes that we should not overlook the inner solar system. Venus, for instance, has not been explored on its surface for nearly four decades, and there has never been a mission to Mercury's surface. Tissot highlights the importance of studying these worlds to enhance our comprehension of the formation processes of terrestrial planets like Earth. By undertaking missions to Venus and Mercury, we can gather crucial data and insights that contribute to a more comprehensive understanding of planet formation and the potential for life beyond our own planet.
The paper in question carries the title "I/Pu reveals Earth mainly accreted from volatile-poor differentiated planetesimals." Alongside Liu and Tissot, the co-authors of the paper include Zhang from the University of Chinese Academy of Sciences, Guillaume Avice from the Université Paris Cité, Institut de physique du globe de Paris, Zhilin Ye from the Chinese Academy of Sciences, and Qing-Zhu Yin from the University of California, Davis. The research received funding from the Chinese Academy of Sciences, the National Science Foundation, a Packard Fellowship for Science and Engineering, the Heritage Medical Research Institute, and Caltech.
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