More than 70% of the earth’s surface is covered by water. The ability of this resource to sustain all life on the planet—including our own lives—is the result of a delicate cycle.
Every drop of rain has completed the same cycle more times than we could possibly hope to count: heat from the sun causes water from the earth’s surface to evaporate and rise into the atmosphere, where it loses temperature, condenses into clouds and then droplets, which finally fall back to the surface as rain.
The amount of water on earth remains constant over time, though the form it takes (reservoirs of ice, salt water, fresh water, subterranean water deposits, and water vapor in the atmosphere) varies depending on the earth’s climate. Currently, more than 97% of the water on our planet is found in its oceans.
Scientists estimate that between 50-80% of the oxygen in the atmosphere actually comes from the oceans—specifically from tiny ocean plants called phytoplankton, which live near the water’s surface and drift with the currents.
Rising ocean temperatures as a result of human-caused climate change are threatening the health of the oceans, causing increases in oxygen-depleted “dead zones.” The critical role of oceans in supporting the entire global ecosystem highlights how imperative it is that we work to keep them healthy.