Physics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.v11a..01b&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #V11A-01
Physics
8100 Tectonophysics, 8115 Core Processes (1507), 8125 Evolution Of The Earth, 9619 Precambrian
Scientific paper
The nature of the geological record is strongly determined by preservation and hence biased by the younger rock record. Although the mean isotopic age of continental crust is ca. 2 Ga, only ca. 7-10 percent of exposed continental crust is Archean, and of this only a very small percentage sheds light on the earliest Archean. The ca. 3.8 Ga Isua rocks are the oldest preserved supracrustal rocks, and an exceedingly small sample of polymetamorphic gneisses extends the rock record to ca. 4 Ga. Only a few multiply recycled detrital zircons represent the earliest record from 4.1 to 4.4 Ga but are extremely rare and, to date, have only been recovered from one Mesoarchean quartzite. It seems counter-intuitive to interpret this early record, or rather lack thereof, in terms of an early Earth characterized by steady-state plate tectonics projecting back as far as 4.4 Ga. At the very least, recycling of a primitive crust and lithosphere must have been so efficient as to be complete. Large continental aggregations, of a size and evolved composition similar to that of the late Archean cratons, are unlikely to have formed prior to ca. 3.6-3.7 Ga. From about this time, the evidence for large, regional-scale gneiss complexes multiplies rapidly in cratons around the world and is locally well preserved. The appearance of the oldest preserved supracrustal rocks at ca. 3.80-3.85 Ga coincides approximately with the interpreted tailing off of the late heavy bombardment. Obviously, for a more complete understanding of early Earth evolution, the Archean geological community has to embrace planetary science and vice versa, fully integrating their respective knowledge bases and methodologies. Other planetary bodies provide different pathways and snap-shots of planetary evolution from initial, hot, accretion to a final state of tectonic inactivity. One impediment to such integration is the lack of a meaningful and complete geological timescale for the Precambrian. Hence, efforts are underway to redefine the Precambrian geological timescale from a common planetary science and extant rock-record perspective. This approach suggests that the evolution of planet Earth defines six eons, separated by major, irreversible "watershed" events. A first eon encompasses the interval from initial accretion to the Moon-forming giant impact. A second eon, the Hadean, captures the interval of nearly complete recycling and terminates with the late heavy bombardment. The onset of the third eon, the Archean, is defined by the first appearance of a supracrustal record. Other major "watershed" events will be discussed.
No associations
LandOfFree
The Geological Record, Non-Steady State Earth Evolution, Major "Watershed" Events, and Their Use as a Basis for a Definitive Geological Timescale does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Geological Record, Non-Steady State Earth Evolution, Major "Watershed" Events, and Their Use as a Basis for a Definitive Geological Timescale, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Geological Record, Non-Steady State Earth Evolution, Major "Watershed" Events, and Their Use as a Basis for a Definitive Geological Timescale will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1178138