from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Of or belonging to the earlier of the two divisions of Precambrian time, from approximately 3.8 to 2.5 billion years ago, marked by an atmosphere with little free oxygen, the formation of the first rocks and oceans, and the development of unicellular life. See Table at geologic time.
- adj. Of or relating to the oldest known rocks, those of the Precambrian Eon, that are predominantly igneous in composition.
- n. The Archean Eon. Also called Archeozoic.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. of or relating to the earliest known rocks formed during the Precambrian Eon
- n. the time from 3,800 million years to 2,500 million years ago; earth's crust formed; unicellular organisms are earliest forms of life
Dial back the clock nearly 4 billion years, to a time called the Archean, and the sun would appear about 30% dimmer than it is now.
The surge of gene births - which the scientists have dubbed the Archean expansion - predate some important changes in Earth's early chemistry, including the appearance of large amounts of oxygen in the atmosphere, say evolutionary biologists Eric Alm and Lawrence David.
There is strong geological evidence that the only "dry land" prior to the early Archean was scattered basaltic islands (sitting over mantle plume "hot spots") similar to the Hawaiian islands.
Actually, during the entire Hadean Eon and part of the Archean Eon the "Earth" was essentially an "all water" planet.
During the Archean Eon life started and was dominated by one-celled prokaryotic life forms.
It seems it happened once in the Archean epoch back when the sun was still cool enough that earth didn't loose its ocean and we were all still bacteria.
In the eastern part of the ecoregion, from Lac St. Jean south to the Gulf of St. Lawrence, and as far west as the Labrador coast, the region is underlain by massive Precambrian and Archean granites and gneisses, and lies between sea level and 600 meters (m) above sea level (asl).
Archean rocks form steeply sloping uplands and lowlands in the Churchill River Upland and Hayes River Upland, while the Archean bedrock of the Lac Seul Upland area forms more broadly sloping uplands and lowlands.
Massive, crystalline Archean rocks form broad, sloping uplands and lowlands, with numerous small lakes and eskers that drain into Great Slave Lake.
This basement was formed during different orogenic phases characterized by large and long-lasting tectonic thermal events that occurred repeatedly during Archean and Proterozoic times.
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