Earth History



Earth History


The following texts are the property of their respective authors and we thank them for giving us the opportunity to share for free to students, teachers and users of the Web their texts will used only for illustrative educational and scientific purposes only.



The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.



Earth History


Earth History: A Brief Summary


Early evolution of Earth


Origin of planet Earth

Most researchers believe that Earth and the other planets formed at essentially the same time from the same primordial material as the Sun

Nebular hypothesis

Solar system evolved from an enormous rotating cloud called the solar nebula

Nebula was composed mostly of hydrogen and helium

Origin of planet Earth

Nebular hypothesis

About 5 billion years ago the nebula began to contract

Assumes a flat, disk shape with the protosun (pre-Sun) at the center

Inner planets begin to form from metallic and rocky clumps of substances with high melting points

Larger outer planets began forming from fragments with a high percentage of ices - water, carbon dioxide, methane and ammonia

Nebular Hypothesis

Formation of Earth’s layered structure

As Earth formed, high-velocity impacts caused the temperature to increase and iron and nickel began to melt and sink toward the center

Buoyant masses of molten rock rose to the surface to produce a primitive crust

Formation of Earth’s layered structure

Early chemical segregation established the three basis divisions of Earth’s in-terior

an iron-rich core

a thin, primitive crust

the mantle between the core and crust

A primitive atmosphere evolved as gas-eous materials escaped from Earth’s interior


Earth’s atmosphere evolves

Primitive atmosphere formed from volcanic gases

A process called outgassing

Water vapor, carbon dioxide, nitrogen, and several trace gases

Very little free oxygen

Water vapor condenses and forms primitive oceans as Earth cools

Bacteria evolve

Plants evolve and photosynthesis produces oxygen

Oxygen content in the atmosphere increases

By about 4 billion years after Earth formed, abundant ocean-dwelling organisms that require oxygen existed


Earth’s history

Precambrian era

4.5 billion to 540 million years ago

88% of Earth's history

Only sketchy knowledge

Most Precambrian rocks are devoid of fossils

Precambrian era

Precambrian rocks

Most are buried from view

Each continent has a "core area" of Precambrian rocks called a shield

Extensive iron ore deposits

Absent are fossil fuels


Precambrian shields


Precambrian era

Precambrian fossils

Most common are stromatolites

Material deposited by algae

Common about 2 billion years ago

Microfossils of bacteria and algae have been found in chert

Southern Africa (3.1 billion years of age)

Lake Superior area (1.7 billion years of age)

Precambrian era

Precambrian fossils

Plant fossils date from the middle Precambrian

Animal fossils date from the late Precambrian

Diverse and multicelled organisms exist by the close of the Precambrian





The geologic time scale


Paleozoic era

540 million years ago to about 248 million years ago

First life forms with hard parts

Abundant Paleozoic fossils

Early Paleozoic history

Southern continent of Gondwanaland exists

Paleozoic era

Early Paleozoic history

North America

A barren lowland

Seas move inland and recede several times and shallow marine basins evaporate leaving rock salt and gypsum deposits

Taconic orogeny, a mountain building event, affects eastern North America 


Reconstruction of early Paleozoic time

Paleozoic era

Early Paleozoic life

Restricted to seas

Vertebrates had not yet evolved

Life consisted of several invertebrate groups




First organisms with hard parts, such as shells – began the Cambrian Explosion

Paleozoic era

Late Paleozoic history

Supercontinent of Pangaea forms

Several mountain belts formed during the movements of the continents

World's climate becomes very seasonal, causing the dramatic extinction of many species

Paleozoic era

Late Paleozoic life

Organisms diversified dramatically

Land plants

Fishes evolve into two groups of bony fish

Lung fish

Lobe-finned fish which become the amphibians



Paleozoic era

Late Paleozoic life

Insects invade the land

Amphibians diversify rapidly

Extensive coal swamps develop

Mesozoic era

248 million years ago to about 65 million years ago

Often called the "age of dinosaurs"

Mesozoic history

Begins with much of the world's land above sea level

Seas invade western North America

Mesozoic era

Mesozoic history

Breakup of Pangaea begins forming the Atlantic ocean

North American plate began to override the Pacific plate

Mountains of western North America began forming

Mesozoic era

Mesozoic life

Survivors of the great Paleozoic extinction

Gymnosperms become the dominant trees

Reptiles (first true terrestrial animals) readily adapt to the dry Mesozoic climate

Reptiles have shell-covered eggs that can be laid on the land

Mesozoic era

Mesozoic life

Dinosaurs dominate

One group of reptiles led to the birds

Many reptile groups, along with many other animal groups, become extinct at the close of the Mesozoic

One hypothesis is that a large asteroid or comet struck Earth

Another possibility is extensive volcanism


Mass Extinctions

Cenozoic era

65 million years ago to the present

Often called the "age of mammals"

Smaller fraction of geologic time than either the Paleozoic or the Mesozoic

North America

Most of the continent was above sea level throughout the Cenozoic era




Cenozoic era

North America

Many events of mountain building, vol-canism, and earthquakes in the West

Eastern North America

Stable with abundant marine sedimen-tation

Eroded Appalachians were raised by isostatic adjustments 

Cenozoic era

North America

Western North America

Building of the Rocky Mountains was coming to an end

Large region is uplifted – Basin and Range province is formed, Rockies are re-elevated, rivers erode the Grand and Black canyons, and volcanic activity is abundant

Cenozoic era

Cenozoic life

Mammals replace reptiles as the dominant land animals

Angiosperms (flowering plants with covered seeds) dominate the plant world

Strongly influenced the evolution of both birds and mammals

Food source for both birds and mammals

Cenozoic era

Cenozoic life

Two groups of mammals evolve after the reptilian extinctions at the close of the Mesozoic



Cenozoic era

Cenozoic life

Mammals diversify quite rapidly and some groups become very large

e.g., Hornless rhinoceros, which stood nearly 16 feet high

Many large animals became extinct

Humans evolve 


Humans Impact on Earth


Key Terms Chapter 14




Prokaryotes, eukaryotes


Evolution, natural selection



Trace fossil


Gymnosperm, angiosperm

Mass extinction


Key Terms Chapter 15

Natural resource

Renewable and non-renewable resources

Fossil fuel

Peat, lignite, bituminous, anthracite coals

Petroleum, oil and natural gas, tar sand and oil shale

Biomass energy

Nuclear energy

Hydroelectric energy

Solar, tidal, wind energy



Source :

Web site link:

Google key word : Earth History file type : doc

Author : not indicated on the source document of the above text

If you are the author of the text above and you not agree to share your knowledge for teaching, research, scholarship (for fair use as indicated in the United States copyrigh low) please send us an e-mail and we will remove your text quickly.


Earth History


If you want to quickly find the pages about a particular topic as Earth History use the following search engine:




Earth History


Please visit our home page Terms of service and privacy page




Earth History