Is the amount of wa­ter on Earth constant?

I won­der if the to­tal quan­tity of wa­ter on Earth is al­ways the same? Or can the wa­ter “leak” into space?

Science Illustrated - - ASK US -

The to­tal quan­tity of wa­ter on Earth has var­ied through­out our planet's ge­o­log­i­cal his­tory and it still does, but the changes are much more in­signif­i­cant now than when the Earth was newly formed.

Earth’s wa­ter forms part of a cy­cle, in which there is a constant ex­change be­tween dif­fer­ent reser­voirs – rivers, lakes, oceans, at­mos­phere, glaciers, and ground wa­ter. Though the wa­ter changes state from solid to liq­uid and gaseous, it has no ef­fect on the to­tal quan­tity of wa­ter.

On the other hand, vol­ca­noes con­tin­u­ously bring new wa­ter to the sur­face. Wa­ter from depths of 50+ km is not con­sid­ered part of the wa­ter cy­cle, so when this wa­ter is forced towards the sur­face, the quan­tity of wa­ter on Earth is sud­denly in­creased. The wa­ter could both have been in­side the planet, since Earth was formed, or it could have come from un­der­neath the con­ti­nen­tal plates. When con­ti­nen­tal drift pulls the plates into the abyss, they melt, and wa­ter is re­leased.

More­over, Earth is sup­plied with wa­ter from space via me­te­ors that con­tain wa­ter. Just like Earth re­ceives ma­te­rial from space, the planet also loses par­ti­cles which es­cape Earth’s at­mos­phere; pri­mar­ily hy­dro­gen, of which we lose 3 kg per sec­ond. The par­ti­cle loss in­flu­ences the quan­tity of wa­ter on Earth, as wa­ter con­sists of one oxy­gen atom and two hy­dro­gen atoms. So, ev­ery time the at­mos­phere sheds hy­dro­gen, we lose one of the build­ing blocks of wa­ter. At the ex­ist­ing rate, Earth will run out of wa­ter in three bil­lion years.

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