Eon: Hadean (/ˈheidiən/)
4.5 BYA - 4 BYA
Description Biology Geology Short
Characteristic: Due to the Earth's early molten state, the Hadean pre dates almost any rock records found to date. The advent of a significant rock record announced the arrival of the following Archean eon. (1)
Description -
The Hadean is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the International Commission on Stratigraphy (ICS), 4 billion years ago. As of 2016, the ICS describes its status as "informal". Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from priscus, the Latin word for "ancient". Other, older texts refer to the eon as the Pre-Archean. (2)
Biology -
Semi-biotic life in the form of trace amounts of carbon minerals "interpreted" as having originated from organic material, were discovered in rock 4.1 billion years old in Western Australia circa 2015. (2)
Short -
Roughly 4.5 Billion Years Ago - Theia, a Mars sized planet, slams into Earth. The impact debris creates the moon and sends both spinning at a near identical turn rate.
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For the next 1.5 billion years the Earth was bombarded with meteorites and remained in a molten state.
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The first evidence of life occurred in thermal vents on the ocean floor. Estimates range from 4.3 - 4.0 billion years ago with the first hard evidence for life not occurring until 3.9 billion years ago at the start of the Archean.