The theory that suggests Earth's surface water originated from asteroid strikes is known as the "late heavy bombardment" hypothesis. While this hypothesis has gained some support, it is important to note that the origins of Earth's water are still a subject of scientific investigation, and there is ongoing research to better understand this process.
That being said, here are some lines of evidence that have been put forward in support of the theory:
Water-rich asteroids: Scientists have studied various types of asteroids and found that a subset of them, called carbonaceous chondrites, contain significant amounts of water in the form of hydrated minerals. These asteroids are thought to have formed in the outer regions of the solar system, where water was more abundant. It is postulated that these water-rich asteroids collided with the early Earth, delivering substantial amounts of water to its surface.
Isotopic composition: The isotopic composition of Earth's water can provide clues about its origin. Isotopes are different forms of an element that have the same number of protons but varying numbers of neutrons. By analyzing the ratios of isotopes in Earth's water, scientists have compared them with the ratios found in various sources such as comets, lunar samples, and meteorites. The isotopic signature of Earth's water is found to be similar to that of carbonaceous chondrites, suggesting a connection between Earth's water and these asteroids.
Deuterium to hydrogen ratio: Deuterium is a heavy isotope of hydrogen, consisting of a proton and a neutron. The ratio of deuterium to hydrogen (D/H ratio) in Earth's water can provide insights into its origin. Studies have shown that the D/H ratio in water from carbonaceous chondrites matches the ratio found in Earth's oceans. This similarity suggests a common source for Earth's water and these asteroids.
Simulation models: Researchers have conducted computer simulations and modeling studies to understand the dynamics of the early solar system. These simulations indicate that the late heavy bombardment period, approximately 4.1 to 3.8 billion years ago, involved a significant number of asteroid impacts on Earth. The energy released during these impacts could have vaporized the surface water and created a steam atmosphere. Over time, this steam would have condensed and formed the oceans we see today.
Lunar samples: The study of lunar samples brought back from the Apollo missions has provided valuable insights into the early solar system. Analysis of these samples revealed the presence of water-bearing minerals and volatile elements, suggesting that the Moon was bombarded by water-rich asteroids as well. This finding lends support to the idea that similar processes could have occurred on Earth.
While these lines of evidence support the theory that asteroid impacts played a significant role in delivering water to Earth, it is important to note that the exact contribution of asteroids and other sources, such as comets, to Earth's water is still a topic of ongoing scientific investigation.