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The deuterium to hydrogen ratio for ocean water on Earth is known very precisely to be (1.5576 ± 0.0005) × 10 −4. [35] This value represents a mixture of all of the sources that contributed to Earth's reservoirs, and is used to identify the source or sources of Earth's water.
When Earth formed around 4.6 billion years ago, some water likely existed in that gas and dust — though much of it would have been vaporized by the sun’s intense heat. How Earth got so much ...
Most water in Earth's atmosphere and crust comes from saline seawater, while fresh water accounts for nearly 1% of the total. The vast bulk of the water on Earth is saline or salt water, with an average salinity of 35‰ (or 3.5%, roughly equivalent to 34 grams of salts in 1 kg of seawater), though this varies slightly according to the amount of runoff received from surrounding land.
Although Earth's hydrosphere has been around for about 4 billion years, [3] [4] it continues to change in shape. This is caused by seafloor spreading and continental drift, which rearranges the land and ocean. [5] It has been estimated that there are 1.386 billion cubic kilometres (333 million cubic miles) of water on Earth.
As of December 2015, the confirmed liquid water in the Solar System outside Earth is 25–50 times the volume of Earth's water (1.3 billion km 3), [10] i.e. about 3.25–6.5 × 10 10 km 3 (32.5 to 65 billion km 3) and 3.25–6.5 × 10 19 tons (32.5 to 65 billion billion tons) of water.
In 2019, 39 million km 2 (15 million sq mi) of Earth's land surface consisted of forest and woodlands, 12 million km 2 (4.6 million sq mi) was shrub and grassland, 40 million km 2 (15 million sq mi) were used for animal feed production and grazing, and 11 million km 2 (4.2 million sq mi) were cultivated as croplands. [270]
The water crisis threatens more than 50% of global food production and risks shaving an average of 8% off countries’ GDPs by 2050, with much higher losses of up to 15% projected in low-income ...
The paradox is this: with the young Sun's output at only 70 percent of its current output, early Earth would be expected to be completely frozen, but early Earth seems to have had liquid water [2] and supported life. [3] The issue was raised by astronomers Carl Sagan and George Mullen in 1972. [4]