GEOL 1020 Lecture Notes - Lecture 24: Uranium-238, Hadean, Paleoproterozoic
18 Oct 2016
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Paleoproterozoic (1600: approximate origin of eukaryotes, transition to oxygen, atmosphere. Archaean (2500: oldest known fossils, oldest known rocks. There are for eon divisions of geologic time. Phanerozoic: we are in this eon right now. The hadean - time between 4. 56 and 3. 85 billion years ago. The hadean has only been recently recognized as a geologic time: samples are not from earth, they are from meteorites. No rocks on earth are this old - except for meteorites and some very (very) rare zircon crystals. During the early hadean, the solar system was forming, probably within a large cloud of a gas and dust around the sun called an accretion disk. The relative abundance of heavier elements (u, th, hf, nb. in our solar system --: suggests that this gas and derived was derived from one o more supernova explosions. These are the result of the demise of an old, massive star.
