Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 44

The competing theory is that water came after Earth was fully formed. This theory asserts that thousands of watery/icy comets and asteroids containing hydroxide (a water precursor) delivered water to Earth. Back then, Jupiter was slightly closer to the sun, and its presence and gravity could have shifted the orbit of these comets and asteroids, putting them on a collision course with Earth. Heat from Earth and the sun melted the ice and formed the ocean.

To test whether Earth’s water came from comets or asteroids, scientists looked at the composition of the water itself. They compared the ratios of hydrogen isotopes (hydrogen atoms with slightly different nuclear masses) among water samples from Earth, asteroids, and comets. None of them matched exactly, but Earth’s water was more similar to that of water contained in asteroids.