Our model, which begins with the degassing of ice from the original asteroid belt, successfully accounts for the amount of water needed to form oceans, rivers and lakes, and even the water buried deep within Earth’s mantle.
One of the earliest hypotheses suggested that Earth’s water was a direct byproduct of the planet’s formation, released via magma during volcanic eruptions, in which most of the emitted gas is water vapour.
By analysing the D/H ratio – the proportion of heavy hydrogen (deuterium) to standard hydrogen – scientists found that Earth’s water more closely matches that of “carbonaceous” asteroids, which bear traces of past water.
This water, now over 4.5 billion years old, has been perpetually renewed through Earth’s water cycle.
Most of this water capture occurred 20 to 30 million years after the Sun’s formation, during a period when the Sun’s luminosity increased dramatically over a brief period of time, increasing the degassing rate of asteroids.
