Geologic Time Scale
division of Earth's history into time units based largely on the types of life-forms that lived only during certain periods
Help scientists divide Earth's history into time units. the oldest rocks on the earth contain only a few fossils.
longest and major divisions in geologic time They are divided into subdivisions called Eras
are divided into subdivisions called Periods.
are divided into smaller units called Epochs.
Precambrian Era
Is the earliest and longest era in the geologic time scale During this era earliest life forms appeared.
Cyanobacteria, Worms and Jelly Fish
1st appeared in the Precambiran time
blue-green bacteria
Is a Cyanobacteria thought to be one of the earliest life forms on Earth, which gave oxygen
Paleozoic Era
followed the Precambrian; Ferns, fish, amphibians and reptiles appeared in the Paleozoic aea
a single large landmass that was composed of all Earths continents joined together. Formed during the Paleozoic era.
Mesozoic Era
followed the Paleozoic Era. Dinosaaurs, birds, small mammals and flowering plants first appeared during Mesozoic time.
Scientist believe Birds
Evolved from dinosaurs
Cenozoic Era
the most recent era and it marks the appearance of humans and large mammals
A group of organisms that reproduce only with members of their group.
Natural Selection
the process by which individuals adapt well to their environment survive and reproduce.
Organic Evolution
change of organisms over geologic time
The order in which different life form appeared on Earth starting with the earliest
Cyanobacteria, Jelly fish, Fish, amphibians, reptiles, birds, mammals
an organism that lived hundreds of millions of years ago with bodies divided into three sections.
1st Geologic Time Unit
Precambrian Era : Cyanobacteria
2nd Geologic Time Unit
Paleozoic Era: Reptiles
3rd Geologic Time Unit
Mesozoic Era : Dinosaurs
4th Geologic Time Unit
Cenozoic Era: Humans