- A scale that subdivides the 4.5- billion-year history of Earth into many different units and provides a meaningful time frame within which the events of the geologic past are arranged.

EONERAPERIODEPOCH PHANEROZOIC CENOZOIC QUATERNARY HOLOCENE PLEISTOCENE TERTIARY PLIOCENE MIOCENE OLIGOCENE EOCENE PALEOCENE MESOZOIC CRETACEOUS “Age of Reptiles” JURASSIC TRIASSIC PALEOZOIC PERMIAN “Age of Amphibians” CARBONI- FEROUS PENNSYLVANIAN MISSISSIPPIAN DEVONIAN “Age of Fishes” SILURIAN ORDOVICIAN “Age of Invertebrates” CAMBRIAN PRECAMBRIAN

EON Two or more geological eras form an Eon, which is the largest division of geologic time, lasting many hundreds of millions of years.

PRECAMBRIAN -means: "before the Cambrian period." -From 4.6 billion years ago to the beginning of the Cambrian Period (about 570 mya)‏

-It is actually composed of three Eons: HADEAN, ARCHEAN, AND PROTEROZOIC.HADEAN ARCHEANPROTEROZOIC. -The Precambrian represents about 88 % of the Geologic Time.

HADEAN EON Hadean ("Hades-like") Eon. 4.5 to 3.9 billion years ago During this era the surface of the Earth was like popular visions about Hades: oceans of liquid rock, boiling sulfur, and impact craters everywhere.

HADEAN EARTH ("Hades-like")

ARCHEAN EON Archean ("Ancient" or "Primitive") Eon. 3.9 to 2.5 billion years ago This eon began about a billion years after the formation of the earth, and things have changed a lot! Mostly everything has cooled down. Most of the water vapor that was in the air has cooled and condensed to form a global ocean.

ARCHEAN EARTH ("Ancient" or "Primitive")

The first life forms evolve - one celled organisms.

The cyanobacteria or "blue-green algae," have left a fossil record that extends far back into the Precambrian - the oldest cyanobacteria-like fossils known are nearly 3.5 billion years old, among the oldest fossils currently known.

PROTEROZOIC EON 2.5 billion years ago to 540 mya First multicellular life: colonial algae and soft-bodied invertebrates appear. Oxygen build-up in the Mid-Proterozoic.

PROTEROZOIC EARTH ("Early Life")

PHANEROZOIC EON -Is derived from Greek words meaning visible life. -It is an appropriate description because the rocks and deposits of the Phanerozoic eon contain abundant fossils that document major evolutionary trends.

-It is composed of three eras: PALEOZOIC, MESOZOIC, and CENOZOIC.

ERA Two or more geological periods comprise an era, which is hundreds of millions of years in duration.

PALEOZOIC ERA Paleo = ancient zoe = life 540 to 248 mya At its beginning, multicelled animals underwent a dramatic "explosion" in diversity, and almost all living animal phyla appeared within a few millions of years.

At the other end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species.

MESOZOIC ERA Meso = Middle zoe = life "THE AGE OF REPTILES" from 248 million to 65 million years ago.

The continents were jammed together at the beginning of the Mesozoic Era, forming the supercontinent of Pangaea, but would start breaking apart toward the middle of the Mesozoic Era.

CENOZOIC ERA Ceno = recent zoe = life 65 Million Years to the Present sometimes called the “Age of Mammals”

PERIOD The period is the basic unit of geological time in which a single type of rock system is formed, lasting tens of millions of years.

PALEOZOIC ERA PERMIAN CARBONIFEROUSPENNSYLVANIAN MISSISSIPPIAN DEVONIAN SILURIAN ORDOVICIAN CAMBRIAN

MESOZOIC ERA CRETACEOUS JURASSIC TRIASSIC

CENOZOIC ERA QUATERNARY TERTIARY