When Earth first formed, it was too hot to retain ice. This means all the water on our planet must have originated from extraterrestrial sources. Studies of ancient terrestrial rocks suggest liquid water existed on Earth as early as 100 million years after the Sun’s formation–practically “immediately” on an astrophysical timescale. This water, now over 4.5 billion years old, has been perpetually renewed through Earth’s water cycle. My research team has recently proposed a new theory to explain how water first arrived on Earth.
