groundwater fossil water residence time

Some groundwater stays underground for more than 10,000 years

>10,000 Years

Water can remain underground for more than 10,000 years. By comparison, water stays in the atmosphere for only about nine days on average before falling again. Very old underground water is often called fossil water.

Large black holes are currently growing, not shrinking

Larger black holes lose less energy through Hawking radiation. Today, a black hole with the mass of a star absorbs more energy from the background radiation of the universe than it loses through Hawking radiation. So for now, it grows rather than slowly evaporating.

Mesopotamian writing grew out of counting

Early Mesopotamian writing began with records of numbers and goods. Over time, people added picture signs and signs for sounds. A system built for accounting gradually became able to write general language.

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groundwater fossil water residence time

Some groundwater stays underground for more than 10,000 years

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