Water is life’s mater and matrix, mother and medium. There is no life without water. ~ Hungarian physiologist Albert Szent-Gyorgyi
Calling this planet Earth is a misnomer. Ours is a watery world. Water’s abundance has been a most significant factor in shaping the planet’s geophysical history.
On early Earth a steamy atmosphere cooled and condensed. Oceans formed from reservoirs in the mantle; possibly by 4.4 BYA; certainly by 3.8 BYA. The water was quite hot, and richer in hydrogen than modern oceans. By 3.4 BYA, ocean waters had cooled to 37 ºC.
H2O on Earth now exists as atmospheric vapor, ice, running water on land, and salted seawater (3.5% salinity, on average). Water reservoirs include the oceans, glaciers, and groundwater.
Groundwater is the deepest and most massive water store. Sponged up in the Earth’s interior is at least 25 times the water in the oceans.
Water is as crucial to the workings of Earth’s interior as it is to Earth’s surface processes. Among other things, it triggers magma generation beneath volcanoes, lubricates deep fault zones, and fundamentally alters the strength and behaviour of Earth’s mantle. ~ American Earth scientist Donna Shillington
Rainwater makes its way into the deep crust where it is heated and pressurized, altering tectonic dynamics. Water sews together the Gaia gyre.
75% of the Earth’s surface is covered by water; overwhelmingly ocean (72%), equivalent to 1.5 billion cubic kilometers, which is 100 times the volume of terrestrial habitats.
In the continents’ current configuration, the Pacific Ocean covers nearly half the Earth’s surface. 81% of the southern hemisphere is ocean, but only 61% of the northern hemisphere.
About half of the world’s ocean is extremely nutrient-poor. ~ German oceanographer Jens Kallmeyer
2% of the 3% of Earth’s surface water that is not oceanic is locked away as ice: in glaciers, ice fields, and snow that coat the polar regions. Antarctica has locked away 75% of the planet’s fresh water; at least for now.
Releasing that frozen storage to further flood the oceans would raise sea levels enough to cover the majority of human populations, which predominantly reside in coastal areas. Ice melts at the poles over the past few decades render dramatic uplift in sea level a certainty. Global warming is a gyre with feedback loops that guarantee accelerating sea-level rise much more quickly than humans will be prepared for.
0.5% of the water left is groundwater. 0.01% lies in lakes and rivers, and aloft in the atmosphere. On the surface, lakes contain 20 times the freshwater that is in all the world’s rivers.
Lovelock observed that the oxygenating work of cyanobacteria stabilized water’s role on Earth, preventing the planetary dehydration that would have otherwise occurred, and probably has on other planets. By switching Earth’s atmosphere from a heavy carbon dioxide component to oxygen, cyanobacteria managed the greenhouse effect by maintaining a cool surface. If the surface heated substantially, such as by volcanic emission of CO2, life flourished in the warm, wet world, restoring equilibrium.
Conversely, if too much carbon was sequestered, such as in limestones, or down subduction zones, the planet cooled to an ice age. Life takes a hit, whereupon volcanic return raises the CO2 level.
Dynamic environmental regulation afforded the abundant water that has been crucial to life on Earth via an intricate interweave of the geological and biological. Biota play an active part in shaping the atmosphere and hydrosphere. Microbes and plants played a prominent role in the air and water cycle before industrialized man began to tear Nature asunder.