[Widdekind]

Over the past few billion years, Earth's Continental Crust has continuously grown, at roughly the rate, of 10% of its present extent, per billion years*.

* Peter Ulmschneider. Intelligent Life in the Universe (2nd ed.), pg. 70. [See attached image]

CONCLUSION: Since Continental Crusts currently cover around one-third of the Earth's surface (~510 million square kilometers), Earth's Continental Crusts will continue to grow by about 5 million square kilometers per billion years (~5 square kilometers per millennium).

[Geosciences-Forum.com]

Log dich ein, um die Werbung auszublenden und alle Funktionen nutzen zu können.

[Widdekind]

Peter Ulmschneider, ibid., pg. 70:

[Platzhalter für ein Bild]

[Geosciences-Forum.com]

Log dich ein, um die Werbung auszublenden und alle Funktionen nutzen zu können.

[Widdekind]

The increase in the fraction of the globe covered by Continental Crusts clearly coincides with a complimentary shrinking of the Seas. And, the (very) early Earth may have been a "water world", completely covered by much deeper oceans, holding perhaps 10 times more water than today*. Indeed, sinking Oceanic Crusts have actually carried, down into the Mantle, around 10-12 times the amount of water currently making up Earth's modern oceans**. Also, the formation of Continental Crust rocks -- to wit, Granite -- somehow involves sea water being mixed into the Mantle, at Subduction Zones***.

* http://www.geosciences-forum.com/htopic598-.html
** http://www.geosciences-forum.com/htopic676-.html
*** History Channel How the Earth was Made (DVD)

CONCLUSION: Earth's Oceanic Crusts have dragged down huge quantities of water in the Mantle. Most such water has been kept at depth. But, some of said water has helped chemically create Granite, & Continental Crusts. Thus, the inexorable growth of Earth's Continental Crusts has come at the cost of the consumption of increasingly copious quantities of this planet's primordial water.

[Widdekind]

ROUGH DRAFT:

Both Earth & Mars were wetter in the deep past (see links above).

CONCLUSION: Planetary Surfaces dry out over time.

COROLLARY: Exo-Planets tend to be much younger than our Solar System*. So, Exo-Planets probably support more water upon their surfaces, at the present epoch.

* http://www.physicsforums.com/showpo...=2199428&postcount=22