for National Geographic News
New evidence supports the theory that the young Earth was a hot and hellish place, scientists say.
Nobody doubts that Earth started out hot. But some researchers argue that it cooled rapidly after its birth, forming continents and oceans early in its history. That Earth, the researchers say, was a lot like the present, with only the occasional meteor strike to stir things up.
(Related story: "Meteorite Impact Reformulated Earth's Crust, Study Shows" [January 12, 2006].)
Before that theory became popular, however, scientists had imagined that frequent volcanic eruptions and earthquakes battered the early Earth, and asteroid impacts repeatedly vaporized its oceans.
This led researchers to call the earliest epoch in Earth's history the Hadean Period. Hades is the Greek word for hell.
Now, a new study of tiny crystals called zircons may throw a spanner in theories of a cool Earth.
The study appears in the August issue of the journal Geology.
One of the main problems with studying the Hadean Period is that no known rock formations have survived to tell us what Hadean conditions might have been like, says Laurence Coogan, a geologist at the University of Victoria, Canada, and one of the study's authors.
"The only material we have is zircons," Coogan said.
Smaller than a grain of pepper, zircons are made of zirconium silicate and other trace materials that crystallize out of cooling magma.
They are important to geologists because they are incredibly durable. They can survive the erosion of their parent rocks, burial in sediment, and recompaction into new rocks.
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