Zircons dating sites Cheap sex chat no membership needed
Eons are divided into eras, which are in turn divided into periods, epochs and ages.The following four timelines show the geologic time scale.
Joshua Schwartz, the paper's first author and a UW Ph. candidate in geology, says the team's research offers another tool to understand the complex processes occurring beneath the Earth's surface.
Older time spans, which predate the reliable fossil record (before the Proterozoic eon), are defined by their absolute age.
Geologic units from the same time but different parts of the world often look different and contain different fossils, so the same time-span was historically given different names in different locales.
Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon.
The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.