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Geologic Time Scale

 Fossil Index

This page is under construction.


Listed with the time scale are interesting events I found surfing the web.  I like seeing the order.


Geologic Time Scale

Divisions are determined by geological or paleontological events, many are based on mass extinctions.  see "Extinctions".  Strata are described in Eon, Era, Period, Epoch, Stage, then by layers of geological series and formations.  Major divisions are world wide.  Most series and formations are regional.  No place on Earth has layers of all the divisions.  It is like a 3D mosaic.  Because of regional discrepancy's in nomenclature, geologists often use Upper (Late), Middle, or Lower (Early).

Why do dates of time periods change from list to list?

When scientists first started studying astronomy, geologic layers and , they believed the Earth as the center of the universe, the world could not be more than a few thousand years old, and the continents were static.  Universities were religious institutions, so knowledge was molded by religious traditions.  Challenging religious concepts is very dangerous.  A tremendous amount of data had to be collected and presented to change commonly held beliefs.

Each generation's understanding is built on previous experiences and should not be ridiculed for what they did not know.  The man who proposed a creation date of over 10,000 years was laughed at, but the evidence supported him.  Now we believe the Earth is 4.6 billion years old and the universe is 11 to 20 billion.  Each year, new studies refine our understanding.


Beginning of Time

Then till now

Big Bang

between 11.2  & 20 billion years ago

The sudden existence of all matter and energy of our universe spreading out from a singularity.  Everything was evenly spaced with a common temperature.  Light was ubiquitous.


1 second later

First growth spurt of the universe, inflation factor of 1043.

Formation of protons and neutrons as the universe expanded.


3 minutes

Formation of the first helium and lithium atoms. Then the end of Fusion.


380,000 years old

The universe expands and cools enough to form neutral hydrogen.

Formation of the Cosmic Microwave Background.

Cosmic Dark Ages

200 million years old

Lasts about 1 billion years

Neutral hydrogen naturally traps visible and UV light making the universe dark.  This Dark Matter does not dissipate its own energy.  (Even today, 80% of all the mater in the universe still consists of Dark Matter.)

CMB currents clump together Dark Matter.  When the mass of Dark Matter became larger than 1000 Suns then the mass was cool enough to let hydrogen clump.

The expansion of the universe kept gravity from collapsing matter back into a singularity.  Currents in the CBM created eddies that kept expansion from tearing matter apart.


600 million years old

Gravity pulled Normal Matter (baryons) together, to the center of Dark Matter clumps that were the size of small galaxies.  More matter means more density.  Enough density allows nuclear fusion and the first stars form.

These stars were larger then any today.  Heavy elements (created inside current stars), which dissipate heat efficiently, did not existed at this time. So these massive suns burned very hot, producing UV photons that ionized the hydrogen and unbound other Normal Matter 1000 light years around them.

These first stars were more than 100 times larger than our sun.  They may have become supernovas within 1 million years.  That explosion would have formed a bubble of Normal Matter within the surrounding Dark Matter cluster (which astronomers still see around galaxies).  Normal Matter clumps together to form more stars.

If a star was over 300 times larger than our sun then it would have imploded to become a large black hole.

The universe was still filled with neutral hydrogen so it still would have appeared dark to a human.

Age of Re-ionization

about 1 billion years old

Enough mater pulls together to re-ionize the universe.  This allows for visible light to be transmitted.


4.5 billion to 500 million years ago

Hadean Eon

4.5  to

3.8 bya

Our solar system forms, possibly from a supernova cloud.

Archaean Eon

3.8 to

2.5 bya

Earth's crust cools and oldest terrestrial rocks form (3.8 bya)

Atmosphere of methane and ammonia

Oldest fossil at 3.5 billion ya is stromatolite

Proterozoic Eon

2.5 bya to

543 mya

First true continents

Abundant fossils of bacteria and archaeans

eukaryotic cells are possibly 1.8 billion years old

Atmospheric oxygen pollution from photosynthetic organisms like stromatolite - First mass extinction

First "red bed" layers from iron oxide

Llano uplift of Texas contains rocks from this age

*Vendian Period

650 to

543 mya

First fossils of soft-bodied multi-cellular organisms

Super-continent of Rodinia

Phanerozoic Eon

544 mya to today

Paleozoic Era

543 to 248 mya

*Cambrian Period

543 to

490 mya

Cambrian Explosion - in a few million years almost all known animal phyla appear and diversify

Breakup of the super-continent of Rodinia

The largest land mass is called proto-Gondwana

No glaciation - mild climate

*Ordovician Period

490 to

443 mya

Super-continent of Gondwana shifted to the southern hemisphere and much of it sunk underwater.  mild climate.

Algae, graptolites, trilobites, brachiopods, cephalopods, coral, crinoids, gastropods.

First bone teeth in early vertebrates called conodonts

Possible - first plants growing above water.

Late Ordovician - massive glaciers drain shallow seas, and drop sea levels.

Mass Extinctions - 60% of all marine invertebrate genera

*Silurian Period

443 to

417 mya

Stabilization of climate, melting of the glaciers, rise in ocean levels

Rapid spread of jawless fish

First coral reefs, first freshwater fish, first jawed fish

On land, relatives of spiders & centipedes

First vascular plants

*Devonian Period

417 to

354 mya

Two small continents and one large in southern hemisphere

First forests of ferns, horsetails, seed plants, trees

First tetrapods, first terrestrial arthropods and arachnids

Many new fish appear.

Mass Extinctions - 365 mya possibly volcanic - Russia/Asia

Mass Extinctions - 354 mya possibly volcanic - Russia/Asia

*Carboniferous Period

354 to

290 mya

Abundant swamps deposited material that became large coal beds across North America, Europe, and Asia.

First amniotic egg

Mild climate decreased club moss and large insects

Increase in tree ferns

**Mississippian Epoch

360 to

325 mya

in USA mostly limestone, crinoids, algae

**Pennsylvanian Epoch

325 to

290 mya

in USA mostly coal

climate with glaciers alternate land as terrestrial or marine

Collision of Laurussia and Godwanaland produces the Appalachian Mountains, Hercynian Mountains of the UK, and the Ural Mountains of eastern Europe.

*Permian Period

290 to

248 mya

Super-continent of Pangaea, super-ocean of Panthalassa, small sea called Tethys

Interior of Pangaea was a seasonal desert, less glaciation

First gymnosperms

End of the Permian - largest mass extinction, mostly marine

Mass Extinctions - 240 mya possibly volcanic - Russia/Asia

Mass Extinctions - 248 mya possibly volcanic - Russia/Asia

Mesozoic Era

248 to 65 mya - "Age of Dinosaurs"

*Triassic Period

245 to

208 mya

Modern gymnosperms

First dinosaurs

Mass Extinctions - 208 mya

*Jurassic Period

208 to

146 mya

Dinosaurs grow huge

First pterosaurs, first birds

Huge marine reptiles, abundant cephalopods

Break-up of Pangaea begins

Gondwanaland split

large trap splits Antarctica from South Africa

Mass Extinctions - ? mya

Mass Extinctions - ? mya

Mass Extinctions - 146 mya

*Cretaceous Period

146 to

65 mya

Middle Cretaceous

First angiosperms - diversified quickly

First Ceratopsians,

First modern mammal and bird groups

Massive volcano removes India from Africa and slams it into Asia forming the Himalayan Mountains

Mass Extinctions - ? mya

Mass Extinctions - ? mya

Mass Extinctions - 65 mya Massive asteroid hits near Chicxulub and leaves a 300 mile wide crater in the Gulf of Mexico.  Killed all non-avian dinosaurs, ammonites, marine reptiles

Cenozoic Era

65 mya to present - "Age of Mammals"

*Tertiary Period

65 to

1.8 mya


**Paleocene Epoch

65 to

54.8 mya

Mass Extinctions - 54.8 mya

**Eocene Epoch

54.8 to

33.7 mya

Oldest known fossils of many modern orders of mammals, early dear and horses were prevalent

**Oligocene Epoch

33.7 to

23.8 mya

Cool climate

First elephants with trunks

First true horses

Many new grasses

Mass Extinctions - ? mya

**Miocene Epoch

23.8 to

5.3 mya

Warm climate then cooler, dry continental interiors

Antarctica becomes isolated and oceans do not mix so continent becomes covered with glaciers

Africa/Arabic plates join Asia

First kelp forests, First grasslands

Mass Extinctions - ? mya

**Pliocene Epoch

5.3 to

1.8 mya

Cooler climate, polar ice, Antarctic extinctions

Land bridge between North & South America appears

Grassy savannas with herds of grazers (mammal) on most continents

Late Pliocene - ice ages

*Quaternary Period

1.8 mya

to present


**Pleistocene  Epoch

1.8 mya to

11,000 ya

dramatic climate change - Ice ages alternate with warmer periods but don't seem to have caused the extinctions

Very large land mammals

Mammoths, horse, camels

First Homo sapiens - spread across most of the world and may have caused the mass extinction at the end of the Pleistocene

**Holocene Epoch

11,000 ya

to present

Time between the last ice age and now.

Generally warm climate except for "mini-ice age"

"Age of Man" - all of recorded history

Time Line uses dates and information from www.ucmp.berkeley.edu

Dark Matter: the unknown stuff that fills 70-80% of the mass of the universe.  Astronomers believe it is the cause of the increasing expansion of the universe.  It may be space itself (Einstein's "cosmological constant"), something that fills in the void like a fog, or the result of a breakdown in our knowledge of gravity when observing huge distances.


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