这个问题有两种方法需要观察。第一个是天文学比地球科学。江南体育网页版地球作为一个整体系统在很大程度上得到控制。它的重力和磁场保留几乎所有的元素。地球失去氢和氦和宇宙射线分解水分子导致的损失令人印象深刻的氢和结果间接损失的水,但是这种损失比海洋的大小无关。更多细节[这][1]。空间尘埃,彗星和小行星从太空返回包含一些水。上估计在一篇文章中,每年50000吨氢工作,失去了每年约450000吨的水。(和400000吨氧气添加结果)。相比,地球上的海洋这些数字的质量很小。 450,000 tons per year, or 450 trillion tons over a billion years is nothing compared to the 1.3 million trillion tons of water Earth has in it's oceans. By the highest estimate, it will take 30 billion years at the current rate and at the Sun's current luminosity for Earth to lose just 1% of it's oceans. *(Will look to update with other estimates)*. As for the rest of the question, once we recognize that loss into space is insignificant, then virtually all water is continuously cycled though the [water cycle or hydrological cycle][2]. Very little water gets destroyed or chemically transformed. Nearly all of it, even of millions or billions of years, evaporates, or, turns into ice, or gets absorbed by plants, or seeps underground, but it always returns. Evaporated water returns to Earth as rain. Water that gets frozen on the ice caps eventually melts back into the oceans. Water absorbed by plants or that seeps underground does eventually get returned to the surface by plate tectonics or volcanism. Plants that store water return it when the plant is eaten. Water is very hard to destroy, so it stays remarkably constant on Earth over time. [1]: https://physics.stackexchange.com/questions/297622/is-the-earth-gaining-or-losing-mass-over-time [2]: https://en.wikipedia.org/wiki/Water_cycle