Earth might have formed much faster than previous hypotheses suggested, arising from tiny pebble-sized particles that gradually accumulated over millions of years. The new hypothesis also implies that instead of icy comets delivering water to Earth, the essential ingredient for life’s existence on the planet came from young Earth itself, drawing water from the space environment. This conclusion holds significant implications for the search for extraterrestrial life, indicating that habitable and water-containing planets around other stars may be more common than currently believed. The study, published on June 14th in the journal Nature, was conducted by Isaac Onyett, a graduate researcher at the Center for Star and Planet Formation at the University of Copenhagen, and his colleagues.
Simulation of the mechanism of Earth formation from tiny pebbles. Image: UHT Zurich.
The research team’s hypothesis points to approximately 4.5 billion years ago when the Sun was still a young star surrounded by a disk of dust and gas. Tiny dust particles were being drawn into the forming planets as they reached a certain size. In the case of Earth, this process of material accretion from the dust and gas disk ensured the planet received its water.
The disk also contained numerous icy particles. While the dust accretion was occurring, it was also absorbing a considerable amount of ice. This process contributed to the presence of water during Earth’s formation period, rather than relying on random events delivering water to the planet 100 million years later.
“There has been a long-standing debate about how planets form,” said Martin Schiller, a geochemist at the University of Copenhagen and a member of the research team. “One hypothesis is that planets arise from collisions between many bodies, gradually increasing in size over 100 million years. In that scenario, the presence of water on Earth would require a chance event.”
An example of such a chance event is icy comets impacting the planet towards the end of the formation period. “If that’s how Earth was formed, then having water on Earth is pretty lucky. Therefore, the chances of water existing on planets outside the Solar System are very low,” shared Schiller.
The research team derived their new hypothesis by using silicon isotopes as a tool to measure the mechanisms of planet formation and the associated timescales. By examining the isotope composition of over 60 meteorites and planets, they were able to establish a relationship between Earth-like rocky planets and other celestial bodies within the Solar System.
The new hypothesis predicts that if a planet orbits a Sun-like star at an appropriate distance, it will have water, according to Professor Martin Bizzarro from the Globe Institute, a co-author of the study.