Water Covering 70% of Earth, Where Did You Come From? [Reading Science]

▲Earth photographed on the 22nd before the 'OSIRIS-REx' spacecraft departed for the asteroid.
[Photo by NASA]

[Asia Economy Reporter Kim Bong-su] Water is one of the essential elements that sustain the blue Earth where living organisms breathe. However, it remains unknown why water is so abundantly present only on Earth. No other planet has yet been discovered where liquid water exists on the surface and supports life like Earth. Scientists have proposed hypotheses ranging from the "comet impact theory," which suggests that comets collided with Earth and delivered large amounts of water, to the "in-situ generation theory," which posits that water was formed during the primordial Earth formation period. Recently, research has also suggested that the Sun supplied water to Earth.

Scientists exploring the origin of water on Earth focused on the ice present in comets. About 4.6 billion years ago, Earth, which was close to the Sun, was a hot, dry planet made of rock and steel. It is believed that comets carrying ice collided with Earth, causing the ice to melt and form the oceans. The fact that comets passing near Earth contain ice led scientists to trust this hypothesis for a time.

In 1986, American professor Louis Frank was a prominent advocate. He claimed that massive comets made of ice collided with Earth, creating the oceans. However, this theory lost credibility after investigations revealed that the isotopes in comet water differed from those in seawater.

▲Close-up footage of the volcano has been released, attracting attention. (Source: Online Community)

Then, in 2002, a remarkable discovery was made. Analysis of zircon, which forms when magma solidifies, provided evidence that water existed during Earth's formation. Steven Mojzsis, a geology professor at the University of Colorado, found zircon crystals estimated to be about 4.38 billion years old. Chemical analysis showed that these minerals formed in an environment where magma cooled rapidly due to the presence of water. This confirmed that early Earth was not a dry, barren star but a place where liquid water existed.

Professor Mojzsis's discovery strengthened the in-situ generation theory, suggesting that when Earth formed, water vapor was included along with dust and gas. Volcanic eruptions and crustal movements on the primitive Earth released water vapor and gases, forming the atmosphere. This water vapor then fell as rain, creating the oceans.

Currently, the mainstream theory in Earth sciences is that Earth's oceans formed due to gravitational interactions between planets. The reason water found in asteroids is similar to Earth's water is that Jupiter's immense gravity caused asteroids to collide and mix, leading to Earth's formation. Among these asteroids were water-rich ones, which contributed to Earth's water content.

Stock photo unrelated to the article. Photo by NASA

Recently, research has also suggested that the Sun was the source of Earth's water. A joint research team from the University of Glasgow in the UK and Curtin University in Australia published a paper on May 29 in the international journal Nature Astronomy, reporting that solar wind reacted with silicate components in dust from asteroids that collided with Earth, forming water.

Solar wind consists of hydrogen ion charged particles, which reacted with small dust particles to produce water on their surfaces. The research team analyzed fragments of the Itokawa asteroid collected by Japan's Hayabusa spacecraft in 2010 and observed water and hydroxyls on olivine grains exposed to solar wind. Experiments also confirmed that irradiating silicate surfaces with hydrogen ions produces water molecules. The team explained, "These results suggest that the surface soil of the Itokawa asteroid contains a certain amount of water and that similar places may exist throughout our galaxy," adding, "It may have contributed some of the water currently present on Earth."

Earth scientists have yet to precisely determine the origin of the vast amount of water on Earth. Many believe that water was generated and coexisted through various pathways. Instead, attention should be paid to the environment that allowed water to remain on Earth.

For example, planets like Mars and Venus are closer to the Sun, causing surface temperatures to be too high, resulting in all moisture evaporating and remaining as water vapor or escaping into space. In contrast, Earth is at an appropriate distance, allowing water vapor to remain due to the greenhouse effect. Earth is located in the Goldilocks zone, the habitable zone where liquid water can exist, at a suitable distance from its central star, the Sun.