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Fraser
2005-Nov-23, 06:36 PM
SUMMARY: Researchers from the University of Colorado at Boulder think they've found evidence that the very early Earth had continents soon after the planet formed, overturning theories that the planet was Moon-like, or covered with oceans. The team analyzed a rare element called hafnium in ancient minerals from the Jack Hills in Western Australia. It showed that continental crusts had formed 4.4 - 4.5 billion years ago, and were then recycled into the Earth's mantle.

View full article (http://www.universetoday.com/am/publish/earth_hafnium.html)
What do you think about this story? post your comments below.

aurora
2005-Nov-23, 08:04 PM
Isn't the olding surviving rock on the Earth's surface something like 4 billion years old? I seem to recall the record is shared by Greenland and Australia.

So if we have crustal rock that is 4 billion years old and stayed afloat and never got subducted, why would it be such a shock to discover that the first crustal rock was somewhat older than that?

LurchGS
2005-Nov-24, 05:19 AM
according to the USGS:

The oldest rocks in North America are not the Morton Gneiss but are the Acasta Gneiss Complex near Great Slave Lake -- 4.03 Ga -- and the Isua Supracrustal rocks in West Greenland -- 3.7 to 3.8 Ga. Both are older than the Morton Gneiss. In addition, the best age for the Earth (4.54 Ga) is based on old, presumed single-stage, leads coupled with the Pb ratios in troilite from iron meteorites, specifically the Canyon Diablo meteorite. In addition, mineral grains (zircon) with U-Pb ages of 4.4 Ga have recently been reported from sedimentary rocks in west-central Australia."

Greg
2005-Nov-24, 10:14 AM
It wasn't that long ago when I posted about some earlier articles on zircon crystals that indicated a much earlier than expected solidification/cooling of the outer crust. If any other doubters are still out there after this one, all I have to say is that the evidence is mounting.

The problem with the old theories regarding that particular topic is that they are only theoretical models and we have yet to be able to detect young terrestrial planets around other solar systems yet to see how fast their surface might be cooling off. In another 50 years we will probably have our hands on actual data from other worlds to work with.