Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 42

Our ocean covers 71 percent of our planet and accounts for nearly 97 percent of its water. That may represent a mere drop in a bucket on a cosmic scale, but it’s respectable on a planetary scale.

If you had that much water in your basement, you’d want to know where it came from, and scientists have been trying to answer that question since, well, about the time they started asking questions. The two big questions are: Was that water always here? and if not, How the heck did it get here? These aren’t exactly “Which came first, the chicken or the egg?” questions, but they’re sort of along the same lines. Either water came from the space debris that formed Earth (so the makings of the ocean were here already), or water arrived via comets or asteroids crashing into Earth after it was already formed. (Note: Comets are made of dust, rock, and ice, and they tend to fly farther from the sun than asteroids do. Asteroids are made mostly of metal and rock and varying amounts of water and tend to hang out closer to the sun. Meteors are comets that enter Earth’s atmosphere.)

In this section, we present the two leading theories of how all that water got here as we explore the ocean’s formation.

Some scientists prefer one theory over the other, but most believe Earth’s water came from multiple sources. Most likely, Earth had some water baked into it during its formation, Earth produced its own water from hydrogen and oxygen, and water was delivered from space via comets and asteroids. That should make everybody happy.