The Ectasian (from Greekectsis, "extension") is the second geologicperiod in the MesoproterozoicEra and lasted from 1400 million years ago to 1200 million years ago. Instead of being based on stratigraphy, these dates are defined chronometrically. Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ... In geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. ... The Mesoproterozoic era is a geologic period that occurred between 1600 and 900 million years ago. ... ERA is an abbreviation for several different things, including: the Equal Rights Amendment, a proposed, but unratified, Constitutional amendment in United States Earned run average, a baseball statistic Engine Room Artificer Education Reform Act Engineering Research Associates, a pioneering computer firm from the 1950s Academy of European Law Trier Explosive... Stratigraphy, a branch of geology, is basically the study of rock layers and layering (stratification). ...
Name derives from continued expansion of platform covers during this period.
Since the Ectasian is only 200 My long, that's a serious matter.
Systematic errors can be caused by extraterrestrial events, by geochemical or biochemical sorting of isotopes, and human error.
The usual reason given for the use of a chronometric system is that we don't have enough biological activity or geochemical change to find useful markers.
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