The oldest rock record on Earth belongs to the Pre-cambrian, including all rocks formed before 543 million years ago, making up about 80 percent of Earth history. The Precambrian is divided in different ways in different parts of the world. The most common usage is to call the youngest period in the Pre-
cambrian the Ediacaran (although it is also known as the Vendian, and in China the Sinian), ranging from 650 to 543 million years ago. This period is named after the Ediacaran Hills in Australia, where fossils from this age are exceptionally well preserved. This was preceeded by the Proterozoic, from 2,500 million to 650 million years ago, divided into the Paleoproterozoic (2.5-1.6 Ga, or billion years ago), the Mesoproterozoic (1.6-1.0 billion years ago), and the Neoproteroic (1.Ga-543 Ma) equivalent, in some usages to the early, middle, and late Proterozoic. The Proterozoic was preceded by the Archean, from 2.5 billion years (Ga) ago to the age of the oldest known rocks (presently 4.2 Ga), and the Archean was preceded by the Hadean, the time from which there is no preserved geologic record.
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Disasters: Why No ones Really 100 Safe. This is common knowledgethat disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.