The Earth’s oceans could have formed not from comets or local protoplanetary materials, but as a result of a collision with another planet—Theia. This conclusion was reached by researchers at the University of Bern, Switzerland, who studied the composition of meteorites and the chemical elements in Earth’s rocks. The study was published in Science Advances.
The analysis showed that the primordial Earth was “dry,” as water molecules were poorly retained in the protoplanetary dust at a distance of 150 million kilometers from the Sun. Comets could also not provide water with the necessary composition, as their water is too enriched in deuterium, whereas Earth’s oceans contain very little.
The scientists tested the giant impact hypothesis, which suggests that about 4.5 billion years ago, Earth collided with a Mars-sized planet. According to the models, an impact with a smaller planet—roughly one-tenth of Earth’s mass—best explains the current chemical composition of the Earth’s mantle, including the ratio of manganese to chromium. A more massive planet would have caused a loss of volatile substances and altered conditions on Earth.
The study’s results support the idea of an extraterrestrial origin for the majority of Earth’s water and help refine scenarios of the early formation of Earth and the Moon. This opens new possibilities for understanding how conditions suitable for the emergence of life were established.
