Earth stands as the only known planet in the universe that supports life, primarily due to its presence of liquid water and a stable atmosphere. However, the conditions that enabled life on Earth were not initially conducive when the planet was formed. The gas-dust cloud from which all the planets in our solar system originated was abundant in volatile elements critical for life, such as hydrogen, carbon, and sulfur. Yet, in the inner solar system—where the rocky planets Mercury, Venus, Earth, and Mars, along with the asteroid belt reside—these essential volatile elements struggled to exist.
Due to the sun's high temperatures, these volatile substances did not condense, remaining primarily in a gaseous state. As a result, they were not integrated into the solid rocky materials that formed the planets. Consequently, the early form of Earth, referred to as proto-Earth, had a minimal presence of these vital substances. Only celestial bodies that formed in the cooler outer regions of the solar system managed to incorporate these essential components.
The timeline and mechanisms through which Earth transformed into a life-sustaining planet remain subjects of ongoing research. A recent study conducted by researchers from the Institute of Geological Sciences at the University of Bern sheds light on this mystery. For the first time, they demonstrated that the chemical composition of early Earth was finalized no later than three million years after the solar system's formation, and this configuration initially rendered the emergence of life impossible. Their findings, published in the journal Science Advances, suggest that a later event played a crucial role in making life on Earth possible.
To reconstruct Earth's early formation process, the research team utilized a combination of isotope and elemental data gathered from meteorites and terrestrial rocks. Through model calculations, they were able to pinpoint the development of Earth's chemical composition relative to other planetary building blocks. Dr. Pascal Kruttasch, the study's first author, noted that a high-precision time measurement system based on the radioactive decay of manganese-53 was employed to determine the precise age of the materials studied. This isotope was present in the early solar system and decays to chromium-53 with a half-life of approximately 3.8 million years.
This innovative method allowed researchers to ascertain ages with an accuracy of less than one million years, even for materials that are billions of years old. The University of Bern's internationally recognized expertise in the analysis of extraterrestrial materials and its leadership in the field of isotope geochemistry made these measurements possible, according to co-author Klaus Mezger, Professor Emeritus of Geochemistry at the Institute.
Using their model calculations, the research team discovered that the chemical signature of proto-Earth—the unique pattern of chemical substances composing it—was complete within three million years after the solar system's formation. Given that our solar system formed around 4.568 billion years ago, this rapid development is quite surprising, as noted by Dr. Kruttasch. The study supports the hypothesis that a later collision with another celestial body, known as Theia, was a pivotal moment that transformed Earth into a life-friendly planet.
Theia likely formed in the cooler outer regions of the solar system, where volatile substances like water accumulated. Dr. Kruttasch explains, "Our results indicate that proto-Earth started as a dry rocky planet, suggesting that the collision with Theia was instrumental in delivering volatile elements to Earth, ultimately paving the way for life." This research provides an important understanding of the conditions necessary for life and the role of significant cosmic events in achieving them.
This groundbreaking study enhances our understanding of the early processes in the solar system and offers insights into how planets capable of supporting life can form. It emphasizes that Earth's current life-friendliness is likely not a result of a continuous evolutionary process, but rather a fortunate cosmic event—the late impact of a foreign, water-rich body. As Mezger aptly states, "This highlights that life-friendliness in the universe is far from guaranteed." The next steps in this research involve a deeper investigation into the collision event between proto-Earth and Theia, aiming to develop comprehensive models that can explain not only the physical properties of Earth and its moon but also their chemical compositions and isotope signatures.
