Geological Time Scale Flashcards
Earth’s history is divided into units of time that make up a ?
geological time scale
We live during the ? Eon
Phanerozoic Eon began 541 million years ago 12% of Earth’s history
Eons
longest subdivisions; based on abundance of fossils.
Hadean, Archean, and Proterozoic are sometimes informally referred to ?
as the “Precambrian”
Eras
marked by significant worldwide changes in the types of fossils present in rock.
Phanerozoic Eon is broken into three eras:
Paleozoic, Mesozoic, Cenozoic.
Periods
Periods – divided eras based on types of existing life globally at a particular time
Epochs
divided periods characterized by differences in life forms.
Why is the GTS useful?
makes showing Earth’s History easier.
It is a clear visual record of the life forms and geologic events .
When does the geological time scale begin?
Geological time begins with a long span of time called Precambrian Time
Earth formed roughly ? years ago.
4.6 billion
Precambrian Time (4.6 billion-544 million years ago)
first several hundred million years atmosphere, oceans and continents began to form.
very few fossils remain
Precambrian rocks have been buried, causing fossils to be changed by heat and pressure
organisms lacked hard parts
Earliest life form to appear
cyanobacteria added oxygen through photosynthesis.
Paleozoic era Phanerozoic
oldest era divided into six periods
Mesozoic era Phanerozoic
middle era divided into three periods
Cenozoic era Phanerozoic
youngest era divided into two periods.
Early Paleozoic consists of the Cambrian and Ordovician periods.
Age of Invertebrates
continents covered by large, shallow inland seas
no life on land; Ordovician period ended with mass extinction
Cambrian Explosion
A period during early Paleozoic Era, most of the major groups of animals first appear in the fossil record.
sudden increase in oxygen to near-modern levels in ocean created this event.
Middle Paleozoic consists of Silurian and Devonian periods
Age of Fish
some invertebrates on land (cockroaches/dragonflies)
continents collided to form mountain ranges
Late Paleozoic consists of Carboniferous and Permian periods
Age of Amphibians (reptiles from amphibians)
continental collisions => formation of Pangaea
largest mass extinction occurred, reason under debate
Mesozoic Era 245 million to 65 million years ago
Age of the Reptiles
Triassic, Jurassic and Cretaceous periods
dinosaurs dominated, small mammals and birds
flowering plants (angiosperms) appeared
Pangaea separated into continents, oceans form
mass extinction from large meteorite impact
Cenozoic Era 65 million to now
Early in Tertiary period, mountains like Himalayans and Alps are formed.
new grasses flowering plants dominated land
mammals evolve
Homo sapiens or humans appeared about 400,000 years ago
We => Quaternary period
