PRE-ARCHEAN (or HADEAN) EON
ABOUT THE GEOLOGIC TIME SCALE
Geologic time is the 4.6 Billion year history of Earth, from its origin to the present, as inferred from the rock record, both on Earth and the Moon, and the geochemical make-up of those two bodies.
Characteristics = the nature of the unique system of rocks and rock formations that define the Period.
is not known precisely, with the uncertainty increasing with increasing age since fossils become rarer and harder to identify in the distant past.
PRE-ARCHEAN EON (or HADEAN EON) - 4.6 to 3.8 Billion years
~4 BYA -- Likely origin of life
This is the "hidden" portion of geologic time as there is little evidence of this time remaining in Earth's rocks.
ARCHEAN EON - 3.8 to 2.5 Billion years
~3.8 BYA -- Oldest known rocks
~3.5 BYA -- Oldest known fossils (single celled organisms resembling bacteria)
3.2 BYA -- First known plants (algae)
PROTEROZOIC EON - 2.5 Billion to 570 Million years
1.2 BYA -- First known animal (jellyfish)
PHANEROZOIC EON - 570 Million years to the Present The eon of complex life
PALEOZOIC ERA - 570 Million years to 245 Million years
The era of ocean life; land animals appear toward the end of this era
Abundant fossils appear in the rock record for the first time
End of the Cambrian denoted by the appearance of fish
Triassic Period - 245 to 208 Million years
150 MYA -- First birds
Climate warmer than at present, with sea level higher
This period (and also the Mesozoic Era) end abruptly with death of the dinosaurs.
The era of mammals.
Tertiary Period - 65 Million to 1.6 Million years ago
Mountain building in Europe and Asia
Pleistocene Epoch -- 1.6 Million to 10,000 years ago
Began with the end of the most recent glaciation