Tuesday, July 05, 2011

Working with extinct animals: Basics (2): Eons and geology


Paleogeologists are scientists who study the ancient geology of the earth.  They examine the past to uncover the genealogy of various landscapes.  Paleogeologists often ask questions such as “Where did those mountains come from?  Was this plain underwater at one time?”  They look at the meanings of time that are displayed in each layer of rock.

By examining rock formations, paleogeologists search for the events of the past.  Through studying eroded areas, they can tell how the earth has changed.  Igneous rocks can be found protruding through sedimentary rocks, which have formed on top of the basalt (lava flow).  Also, fossils from the sea are often found embedded in mountain rocks, indicating that the seafloor has risen. 

Paleogeologists tell time through examining the segments of rock (referred to as “strata”).  These “layers of time” is known as chronostratigraphy, while geochronology is “periods of time”.  The “layers of rock time” is roughly equal to the periods of time.  Therefore “stage”, the shortest time in rock layers, is usually made up of a consistent set of fossils.  “Stage” in chronostratigraphy is “age” in geochronology.  The other “layers of time” are “series” (epoch), “system” (period), “erathem” (era) and “econothem” (eon).  The stages combine into a series, while the series combine into a system, systems into an erathem, and finally erathems into an econothem.

Earth’s Time Line
SUPEREON: Precambrian (Cryptozoic)
EON: Hadean
EON: Archean
EON: Proterozoic

SUPEREON: Cambrian
EON: Phanerozoic

ERA: Paleozoic
PERIOD: Cambrian
PERIOD: Ordovician
PERIOD: Silurian
PERIOD: Devonian
PERIOD: Carboniferous
PERIOD: Permian

ERA: Mesozoic
PERIOD: Triassic
PERIOD: Jurassic
PERIOD: Cretaceous

ERA: Cenozoic
PERIOD: Paleogene (or Tertiary)
EPOCH: Paleocene
EPOCH: Eocene
EPOCH: Oligocene

PERIOD: Neogene (or Tertiary)
EPOCH: Miocene
EPOCH: Pliocene

PERIOD: Quaternary
EPOCH: Pleistocene
EPOCH: Holocene

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