Earth's Geological Timeline


It is now generally assumed that planets are formed by the gathering and binding of gas and dust in a cosmic cloud , but there is no way of estimating how long this process takes . Our Earth acquired its present size , more or less , between 4,000 million and 5,000 million years ago .Life on Earth originated about 2,000 million years ago , but there are no good fossil remains from periods earlier than the Cambrian , which began about 550 million years ago .The largely unknown past before the Cambrian period is referred to as the Pre-Camprian and is subdivided into the lower (or older) and Upper (or younger) Pre-Cambrian- also called the Archaeozoic and Proterozic Eras .
The known geological history of Earth since the beginning of the Cambrian period is subdivided into three giant chunks of time , or eras , each of which includes a number of shorter periods . They , in turn , are subdivided into even shorter subperiods .In a subpriod , a certain section may be espicially well known because of abundant fossil finds .such a section is called a formation,and it is usually identified by a place name.



Paleozoic Era

This era began 550 million years ago and lasted for 355 million years.



period year 1 long subperids creatures that appeared
cambrian 70 early cambrian-middle cambrian-late cambrian invetebrate sea life of many types appear and multiply during this and the following period.
ordovician 85 early ordovician-late ordovician first known fishes
silurian 40 early silurian-late silurian gigantic sea scorpions.
devonian 50 early devonian -late devonian number of fishes and other forms of sea life increases;land still largely lifeless.
carboniferous 85 mississippian(early) pennsylvanian(late) early insects and first known amphibians.
permain 25 early permain-late permain early reptiles and mammals;earliest form of turtles.
1.In million of years


Mesozoic Era

This era began 195 million years ago and lasted for 135 million years.Popular name:Age of Repiles.

period years 1 long subperids creatures that appeared
triassic 35 buntsandstein(early)-muschelkalk(middle)keuper(late) many reptiles fit for going to sea;early large dinosaurs;somewhat later,flying reptiles;arliest known birds.
jurassic 35 black jurassic,or lias(early);brown jurassic,or dogger(middle)white jurassic,or malm(late) many reptiles fit for going to sea; early large dinosaurs;somewhat later,flying reptiles;earliest known birds.
cretaceous 65 early cretaceous late cretaceous more dinosaurs;more birds;creatures with pouches (marsupials).
1.In million of years.


Cenozoic Era

This era began 60 milion years ago and includes the geological present.Popular name:Age of Mammals.

period years 1 long subperiods creatures that appeared
tertiary c.60 paleocene-eocene-oligocene-miocene-pliocene first mammals other than marsupials;formation of amber(a substance left by a fossil),abundant insect population;early bats;steady increase of large mammals;mammals closely resembling today's animals.
plesistocene(popular name:ice age) 1 four major glacial formations named gunz,mindle,riss,and wurm,orginally the names of rivers.last glaciation ended 10,000 to 15,000 years ago. various forms of early humans.
holocene the present the last 3,000 years ago calles "history".
1.In million of years

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Last Modified : 5 Sep. 2001
Created By#C0115361 Team