Astronomical and geological evidence indicates that the Universe is approximately 13,700 million years old, and our solar system is about 4,567 million years old. Earth's Moon formed 4,450 million years ago, just 50 million years after the Earth's formation. Because the composition of the rocks retrieved from the Moon by the Apollo missions is very similar to rocks from the Earth, it is thought that the Moon formed as a result of a collision between the young Earth and a Mars-sized body, sometimes called Theia, which accreted at a Lagrangian point 60° ahead or behind the Earth. A cataclysmic meteorite bombardment (the Late Heavy Bombardment) of the Moon and the Earth 3,900 million years ago is thought to have been caused by impacts of planetesimals which were originally beyond the Earth, but whose orbits were destabilized by the migration of Jupiter and Saturn during the formation of the solar system. The Mars Reconnaissance Orbiter and the Mars Global Surveyor have found evidence that the Borealis basin in the northern hemisphere of Mars may have been created by a colossal impact with an object 2,000 kilometers in diameter at the time of the Late Heavy Bombardment.
Approximately 3,000 million years ago, the earth was cool enough for land masses to form. The supercontinent Rodinia was formed about 1100 million years ago, and it broke into several pieces that drifted apart 750 million years ago. Those pieces came back together about 600 million years ago, forming the Pan-African mountains in a new supercontinent called Pannotia. Pannotia started breaking up 550 million years ago to form Laurasia and Gondwana. Laurasia included what are now North America, Europe, Siberia, and Greenland. Gondwana included what is now India, Africa, South America, and Antarctica. Laurasia and Gondwana rejoined approximately 275 million years ago to form the supercontinent of Pangea. The break up of Pangea, which still goes on today, has contributed to the formation of the Atlantic Ocean.
|(mya = million years ago)|
The times are approximate and may vary by a few million years.
(4567 to 542 mya)
Hadean Eon (4567 to 4000 mya)
- 4650 mya: Formation of chondrules in the Solar Nebula
- 4567 mya: Formation of the Solar System
Sun was only 70% as bright as today.
- 4500 mya: Formation of the Earth.
- 4450 mya: The Moon accretes from fragments
of a collision between the Earth and a planetoid;
Moon's orbit is beyond 64,000 km from the Earth.
Earth day is 7 hours long
- Earth's original hydrogen and helium atmosphere
escapes Earth's gravity.
- 4455 mya: Tidal locking causes one side
of the Moon to face the Earth permanently.
- 4280 mya: Water started condensing in liquid form.
- 3900 mya: Cataclysmic meteorite bombardment.
The Moon is 282,000 km from Earth.
Earth day is 14.4 hours long
- Earth's atmosphere becomes mostly
carbon dioxide, water vapor,
methane, and ammonia.
- Formation of carbonate minerals starts
reducing atmospheric carbon dioxide.
- There is no geologic record for the Hadean Eon.
Archean Eon (4000 to 2500 mya)
Eoarchean Era (4000 to 3600 mya)
- 4000 mya: The Earth's crust cooled and solidified.
- Atmospheric pressure ranged from 100 to 10 bar.
- Earth day is 15 hours long
Paleoarchean Era (3600 to 3200 mya)
- 3600 mya: Formation of first supercontinent Vaalbara.
- 3500 mya: Monocellular life started (Prokaryotes).
First known oxygen-producing bacteria:
cyanobacteria (blue-green algae) form stromatolites
- Oldest unambiguous microfossils date from this era.
Mesoarchean Era (3200 to 2800 mya)
- 3000 mya: Atmosphere has 75% nitrogen,
15% carbon dioxide.
- Sun brightens to 80% of current level.
- 2900 mya: Pongola glaciation occurred.
Neoarchean Era (2800 to 2500 mya)
- 2800 mya: Break up of supercontinent Vaalbara.
- Oldest record of Earth's magnetic field.
- 2700 mya: Supercontinent Kenorland formed.
- Photosynthetic organisms proliferate.
Proterozoic Eon (2500 to 542 mya)
Paleoproterozoic Era (2500 to 1600 mya)
Siderian Period (2500 to 2300 mya)
- Stable continents first appeared.
- 2500 mya: First free oxygen is found
in the oceans and atmosphere.
- 2400 mya: Great Oxidation Event,
also called the Oxygen Catastrophe.
Oxidation precipitates dissolved iron
creating banded iron formations.
Anaerobic organisms are poisoned by oxygen.
- 2400 mya: Start of Huronian ice age
Rhyacian Period (2300 to 2050 mya)
- 2200 mya: Organisms with mitochondria
capable of aerobic respiration appear.
- 2100 mya: End of Huronian ice age
Orosirian Period (2050 to 1800 mya)
- Intensive orogeny (mountain development)
- 2023 mya: Meteor impact, 300 km crater
Vredefort, South Africa 
- 2000 mya: Solar luminosity is 85% of current level.
- Oxygen starts accumulating in the atmosphere
- 1850 mya: Meteor impact, 250 km crater
Sudbury, Ontario, Canada 
Statherian Period (1800 to 1600 mya)
- Complex single-celled life appeared.
- Abundant bacteria and archaeans.
Mesoproterozoic Era (1600 to 1000 mya)
Calymmian Period (1600 to 1400 mya)
- Photosynthetic organisms continue to proliferate.
- Oxygen builds up in the atmosphere above 10%.
- Formation of ozone layer starts blocking
ultraviolet radiation from the sun.
- 1500 mya: Eukaryotic (nucleated) cells appear.
Ectasian Period (1400 to 1200 mya)
- Green (Chlorobionta) and red (Rhodophyta) algae abound.
Stenian Period (1200 to 1000 mya)
- 1200 mya: Spore/gamete formation indicates
origin of sexual reproduction.
- 1100 mya: Formation of the supercontinent Rodinia
Neoproterozoic Era (1000 to 542 mya)
Tonian Period (1000 to 850 mya)
- 1000 mya: Multicellular organisms appear.
- 950 mya: Start of Stuartian-Varangian ice age
- 900 mya: Earth day is 18 hours long.
The Moon is 350,000 km from Earth.
Cryogenian Period (850 to 630 mya)
- 750 mya: Breakup of Rodinia and
formation of the supercontinent Pannotia
- 750 mya: End of last magnetic reversal
- 650 mya: *Mass extinction of 70% of dominant sea plants
due to global glaciation ("Snowball Earth" hypothesis).
The Moon is 357,000 km from Earth.
Ediacaran (Vendian) Period (630 to 542 mya)
- 600 mya: Earth day is 20.7 hours long.
- 590 mya: Meteor impact, 90 km crater
Acraman, South Australia
- 580 mya: Soft-bodied organisms developed:
Jellyfish, Tribrachidium, and Dickinsonia appeared.
- 570 mya: End of Stuartian-Varangian ice age
Shelled invertebrates appeared
- 550 mya: Pannotia fragmented into Laurasia and Gondwana
(542 mya to present)
Paleozoic Era (542 to 251 mya)
Cambrian Period (542 to 488.3 mya)
- Abundance of multicellular life.
- Most of the major groups of animals first appear
Tommotian Stage (534 to 530 mya)
- 510 mya: Vertebrates appeared in the ocean.
Solar brightness was 6% less than today.
Ordovician Period (488.3 to 443.7 mya)
- diverse marine invertebrates, such as trilobites,
- First green plants and fungi on land.
- Fall in atmospheric carbon dioxide.
- 450 mya: Start of Andean-Saharan ice age.
- 443 mya: Glaciation of Gondwana.
*Mass extinction of many marine invertebrates.
Second largest mass extinction event.
49% of genera of fauna disappeared.
Silurian Period (443.7 to 416 mya)
- 420 mya: End of Andean-Saharan ice age.
- Stabilization of the earth's climate
- Land plants and coral reefs appeared
- First fish with jaws - sharks
- Insects (spiders, centipedes), and plants appear on land
Devonian Period (416 to 359.2 mya)
- Ferns and seed-bearing plants (gymnosperms) appeared
- Formation of the first forests
- Earth day is ~21.8 hours long.
- 400 mya: Land animals appeared, wingless insects
- 375 mya: Vertebrates with legs, such as Tiktaalik appeared.
- Atmospheric oxygen level is about 16%
- First amphibians appear.
- 374 mya: *Mass extinction of 70% of marine species.
This was a prolonged series of extinctions
occurring over 20 million years.
Evidence of anoxia in oceanic bottom waters,
and global cooling. Surface temperatures dropped
from about 93°F (34°C) to about 78°F (26°C)
- 370 mya: First trees appeared
- 359 mya: Meteor impact, 40 km crater
Carboniferous Period (359.2 to 299 mya)
Mississippian Epoch (359.2 to 318.1 mya)
- 350 mya: Beginning of Karoo ice age.
- Large primitive trees develop
- First winged insects
- Forests consist of ferns, club mosses, horsetails, and gymnosperms.
- Oxygen levels increase
- 324 mya: Synapsid vertebrates, the ancestors of mammals,
appear on land.
- Seas covered parts of the continents
- Animals laying amniote eggs appear (318 mya)
Pennsylvanian Epoch (318.1 to 299 mya)
- 300 mya: First reptiles (diapsids) appeared.
They were ancestors of crocodiles, dinosaurs and pterosaurs.
- Atmospheric oxygen levels reach over 30%
- Earth day is ~22.4 hours long.
The Moon is 375,000 km from Earth.
- Giant arthropods populate the land
- Transgression and regression of the seas
caused by glaciation
- Deposits of coal form in Europe, Asia,
and North America
Permian Period (299 to 251 mya)
- 275 mya: Formation of the supercontinent Pangea
- Conifers and cycads first appear
- Earth is cold and dry
- Sail-backed synapsids like
Edaphosaurus and Dimetrodon appeared
- 260 mya: End of Karoo ice age.
- 251 mya: *Mass extinction (Permian-Triassic)
- Possible 480km-wide meteor crater in the
Wilkes Land region of Antarctica 
- Period of great volcanism in Siberia releases
large volume of gases (CO2, CH4, and H2S) 
- Oxygen (O2) levels dropped from 30% to 12%
Carbon dioxide (CO2) level was about 2000 ppm
Temperatures reach 50-60°C on land, and 40°C at the sea-surface.
Earth's worst mass extinction eliminated
90% of ocean dwellers, and 70% of land
plants and animals.
Mesozoic Era (251 to 65.5 mya)
Triassic Period (251 to 199.6 mya)
- Break-up of Pangaea starts
- Survivors of P-T extinction spread and recolonize
- Reptiles populate the land.
- 240 mya: Sea urchins (Arkarua) appear
- 235 mya: Evolutionary split between dinosaurs and lizards
- Giant marine ichthyosaurs and plesiosaurs populate the seas
- First small dinosaurs such as coelophysis appear on land
- Adelobasileus proto-mammal emerged (225 mya)
- 214 mya: Meteor impact, 100 km crater
Manicouagan, Quebec, Canada 
- 205 mya: First evidence of mammals: Morganucodon
- 201 mya: Volcanism in Central Atlantic Magmatic Province
*Mass extinction killed 20% of all marine families
Jurassic Period (199.6 to 145.5 mya)
- Earth is warm. There is no polar ice
- Cycads, conifers and ginkgoes are the dominant plants
- Age of the dinosaurs
- Giant herbivores and vicious carnivores
dominate the land
- Flying reptiles (Pterosaurs) appeared.
- 180 mya: North America separates from Africa
- 167 mya: Meteor impact, 80 km crater
Puchezh-Katunki, Russia 
- 166 mya: Evolutionary split of monotremes from primitive mammals
- 150 mya: First birds like Archaeopteryx appear
- 148 mya: Evolutionary split between
marsupial and eutherian mammals
- 145 mya: Meteor impact, 70 km crater
Morokweng, South Africa 
Cretaceous Period (145.5 to 65.5 mya)
- Period of Active Crust Plate Movements
- 133 mya: Meteor impact, 55 km crater
Tookoonooka, Australia 
- 125 mya: Africa and India separate from Antarctica
- Global warming event starts (120 mya)
Carbon dioxide levels were 550 to 590 ppm 
- Proliferation of single-cell organisms (diatoms, dinoflagellates,
and calcareous nannoplankton) changed ocean composition.
- Flowering plants (angiosperms) appeared
- 110 mya: Crocodiles appeared
- South America breaks away from Africa (105 mya)
- Formation of the Atlantic Ocean
- Earth has no polar ice
- Birds and oldest group of living placental mammals developed
- 100 mya: Earth's magnetic field is
3 times stronger than today.
First ants (hymenoptera) appeared
- 90 mya: Global warming event ends
- Western Interior Seaway separates North America
into Laramidia (west) and Appalachia (east)
- 70 mya: Meteor impact, 65 km crater
Kara, Russia 
Caution: Do not poke T. rex
- 68 mya: Tyrannosaurus rex thrived
- 67 mya: Deccan Traps volcanic eruptions start in India
and produce great volume of lava and gases.
- 65.5 mya: Meteor impact, 170 km crater
Chicxulub, Yucatan, Mexico 
- *Mass extinction of 80-90% of marine species
and 85% of land species, including the dinosaurs.
Cenozoic Era (65.5 mya to today)
The five major mass extinctions events occurred during the terminal Ordovician (443 mya), Late Devonian (374 mya), terminal Permian called the "Great Dying" (251 mya), terminal Triassic (201), and terminal Cretaceous called the K/T event (65.5 mya).
Humans as agents of environmental change
Some scientists have tried to correlate the migration of humans to America with the extinction of the megafauna of the Pleistocene Epoch while others feel that weather changes brought about by the explosion of an asteroid or comet over North America might have been responsible. There is no doubt that human activities can have a substantial impact on the environment and native species. The dodo, a flightless bird indigenous to Mauritius, became extinct in the late 17th century from massive hunting and the introduction of animals such as dogs, pigs, and cats. The Passenger Pigeon went from being the most common bird in North America to extinction by the end of the 19th century due to hunting and loss of habitat by deforestation. Overfishing the costal waters of California in 1945 produced 235,000 tons of fish, but in 1948 only 15,000 tons of fish were caught which led to the collapse of Cannery Row. The Dust Bowl was a man-made ecological disaster caused by deep plowing of the top soil of the Great Plains which destroyed native grasses whose roots had protected the soil from erosion. Drought and wind created a period of severe dust storms between 1930 and 1936. Soils that had been fertile became incapable of growing crops after the top soil was blown away. The contemporary destruction of tropical forests by the logging industry and the large-scale clearing of forests to plant commercial crops is already having harmful ecological effects that are likely to become worse if non-sustainable practices continue to be used.
The Earth's near-term future
Human industrial activity that relies on burning fossil fuels, such as coal and petroleum products, has been generating the greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), in large quantities since about 1750. The chart below shows the levels of atmospheric carbon dioxide during the last millennium and its sharp rise during the last century. Atmospheric models predict that elevated greenhouse gases will cause global warming and influence weather patterns that will melt polar ice and destroy the habitat of animals such as the polar bear. The increase of global temperatures will also reduce the amount of snow deposited on mountains thus decreasing the flow of water in rivers which are now used for navigation, irrigation, and as sources of potable water. Carbon dioxide will also increase the acidity of sea water and threaten coral reefs and shell-building oceanic life forms.
Today, the concentration of atmospheric carbon dioxide is 380 parts per million (ppm) and the North Pole's mean annual temperature is -20°C. Analysis of core sediments in the Arctic Circle indicate that 55 million years ago, the carbon dioxide concentration was 2,000 ppm and the North Pole's temperature averaged 23°C (73.4°F). Satellite images by NASA show approximately a 20% reduction in the Earth's minimum ice cover between 1979 and 2003. Arctic perennial sea ice has been decreasing at a rate of 9% every ten years. At this rate, the summertime Arctic Ocean will be ice-free before the year 2100.
There is a large amount of water stored as ice over the landmasses of Greenland and Antarctica. If the ice sheets melt, the resulting rise in global sea level will flood many coastal areas around the world. The Greenland ice sheet contains enough water to increase the global sea level by 24 feet (7.3 meters), the West Antarctic ice sheet could raise sea level by 19 feet (5.8 meters), and the East Antarctic ice sheet could raise the sea level globally by 170 feet (51.8 meters). The combined effect of melting all the ice on Greenland and Antarctica would result in a sea level rise of 213 feet (65 meters).
Using computer models, scientists at the University of Arizona Department of Geosciences have created maps that show areas susceptible to rises in sea level (in red). The following map shows that a 6-meter (20-foot) rise would flood Miami, Fort Lauderdale, Tampa, and the entire Florida coastline, as well as parts of Orlando and other inland areas. Most of the city of New Orleans, Louisiana will disappear under water if the sea rises six meters. Some scientists have warned that by the year 2200, at the current rate of greenhouse gas emissions from human activities, the atmospheric levels of carbon dioxide, methane, and nitrous oxide will be at the same levels associated with mass-extinction events in the Earth's past.
The Earth's long-term future
The future of the Earth is linked to the fate of the Sun. The Sun is halfway through its life cycle and will exhaust its supply of hydrogen fuel in around 4,000 million years. As the Sun cools, its core will collapse and its atmosphere will expand transforming the Sun into a red giant star. The swelling Sun will engulf the planets closest to it, and the Earth will be completely vaporized. The Sun will die in several stages. When its core crashes inwards, it will start fusing helium atoms into carbon. When the helium supply runs out, the center will collapse again and form a white dwarf star that will become dimmer until its light finally fades. The final collapse of stars which are a few times larger than the Sun ends in a massive supernova explosion that leaves behind a rapidly spinning neutron star.
Long before the Sun becomes a white dwarf, 2,000 million years from now, our Milky Way Galaxy is predicted to collide with the Andromeda Galaxy. The collision will take place for several million years and result in one combined super galaxy named Milkomeda. The sun may become part of the Andromeda system during the collision and could eventually end up far away from the new merged galactic center. The Earth may also eventually lose its Moon. Scientists using the laser ranging retroreflector positioned on the Moon in 1969 by the Apollo 11 astronauts have determined that the Moon is receding from Earth at a rate of about 3.8 centimeters per year.
|Earth's Long-Term Future|
+200 years: Possible global warming event caused by anthropogenic carbon dioxide (CO2)
+1500 my: Sun is about 6000 million years old and 15% brighter than today.
+2000 my: Milky Way Galaxy starts colliding with Andromeda Galaxy.
+3000 my: Solar system becomes part of the new Milkomeda Galaxy.
+4000 my: Sun is about twice as bright as today and its radius is 40% greater.
Sun starts to exhaust its supply of hydrogen.
+5000 my: Sun starts changing into a red giant star, 3 times its present size.
Earth is engulfed by the red giant Sun.
+10000 my: Red giant Sun collapses and becomes a white dwarf.
+20000 my: White dwarf Sun becomes a black dwarf.
Aeon - See Eon.
Age - An age is a unit of geological time shorter than an epoch, usually lasting several million years.
Archean, Archaean - An eon of geologic time extending from about 4000 to 2500 million years ago. Derived from the Greek archaios meaning "ancient". The Archean eon is divided into four eras: Eoarchean, Paleoarchean, Mesoarchean, and Neoarchean.
Cambrian - The first period of the Paleozoic Era, during which most modern animal phyla developed. The name derives from Medieval Latin Cambria "Wales".
Cenozoic, Caenozoic, Cainozoic - The current geologic era, which began 65.5 million years ago and continues to the present. The word comes from the Greek kainos "new" + zoe "life".
Cretaceous - A Period from 145 to 65.5 million years ago divided into two epochs:
The Early Cretaceous Epoch had six Ages: Cenomanian, Turonian, Coniacian, Santonian, Campanian, and Maastrichtian.
The Late Cretaceous Epoch had six Ages: Berriasian, Valanginian, Hauterivian, Barremian, Aptian, and Albian.
Eocene Epoch - An epoch from 54.8 to 33.9 million years ago with four Ages: Ypresian, Lutetian, Bartonian, and Priabonian.
Eon - A primary division of geologic time lasting over 500 million years, four of which have been defined: Hadean, Archean, Proterozoic, and Phanerozoic. Eons are divided into Eras, which are in turn divided into Periods, Epochs and Ages.
Epoch - A division of geologic time lasting tens of millions of years. Epochs are subdivisions of geologic periods.
Era - A division of geologic time of several hundred million years in duration. An era is smaller than an eon and longer than a period.
Geologic Time Scale - A categorization of geological events based on successively smaller time spans: eons, eras, periods, epochs, and ages.
Hadean - The earliest eon in the history of the Earth from the first accretion of planetary material until the date of the oldest known rocks. The name "Hadean" derives from the Greek Hades "Hell".
Holocene - An epoch starting 11,400 years ago to today. From holo- "whole" + Greek kainos "new".
Jurassic - A Period from 200 to 145 million years ago divided into three epochs:
The Early Jurassic Epoch has four Ages: Hettangian, Sinemurian, Pliensbachian, and Toarcian.
The Middle Jurassic Epoch has four Ages: Aalenian, Bajocian, Bathonian, and Callovian.
The Late Jurassic Epoch has three Ages: Oxfordian, Kimmeridgian, and Tithonian.
Mesoproterozoic - an era with three periods: Calymmian, Ectasian, and Stenian.
Mesozoic - An era of time during the Phanerozoic eon lasting from 251 million years ago to 65.5 million ago. Derived from the Greek mesos "middle" + zoe "life".
Miocene Epoch - An epoch from 23.03 to 5.3 million years ago with six Ages: Aquitanian, Burgidalian, Langhian, Serravalian, Tortonian, and Messinaian. The name is derived from Greek meiōn "less" + kainos "new".
Neogene - A period from 23.03 to today. This is the new name given to the time starting from the Miocene Epoch to today.
Neoproterozoic - An era with three periods: Tonian, Cryogenian, and Ediacaran.
Oligocene Epoch - An epoch from 33.9 to 23.03 million years ago with two Ages: Rupelian and Chattian. Derived from oligo- "few" + Greek kainos "new".
Paleocene, Palaeocene Epoch - An epoch from 65.5 to 54.8 million years ago with three Ages: Danian, Selandian, and Thanetian.
Paleogene - A period from 65.5 to 23.03 million years ago. This is the new name given to the first portion of the Tertiary Period.
Paleoproterozoic - an era with four periods: Siderian, Rhyacian, Orosirian, and Statherian.
Paleozoic, Palaeozoic - An era of geologic time lasting from 542 to 248 million years ago. Derived from the Greek palai "long ago, far back" + zoe "life".
Period - A division of geologic time lasting tens of millions of years which shorter than an era and longer than an epoch.
Phanerozoic - The most recent eon of geologic time beginning 542 million years ago and continuing to the present. Derived from the Greek phaneros "visible" + zoe "life".
Pleistocene - An epoch from 2.58 mya to 11,400 years ago. Derived from Greek pleistos "most" + kainos "new".
Pliocene - An epoch from 5.3 to 2.58 million years ago with two Ages: Zanclean and Piacenzian. Derived from Greek pleiōn "more" + kainos "new".
Precambrian - Geologic time from the beginning of the earth to the beginning of the Cambrian Period of the Paleozoic Era.
Proterozoic - The geologic eon lying between the Archean and Phanerozoic eons, beginning about 2500 and ending 542 million years ago. Derived from the Greek proteros "earlier" + zoe "life". The Proterozoic eon is divided into the Paleoproterozoic era, Mesoproterozoic era, and Neoproterozoic era.
Quaternary - An informal sub-era from 2.58 or 1.8 mya to today. The Quaternary is traditionally associated with the Holocene and Pleistocene, but an alternative definition sets its start during the cycle of glacials and interglacials around 2.6 mya.
Stage - A succession of rock strata laid down in a single age on the geologic timescale.
Tertiary - An informal sub-era from 65.5 to 2.58 or 1.8 million years ago, depending on how the Quaternary is defined. The Tertiary overlaps with the Neogene Period and is divided into five epochs:
Paleocene, Eocene, Oligocene, Miocene, and Pliocene.
Triassic - A Period from 251 to 200 million years ago divided into three epochs:
The Early Triassic Epoch has two Ages: Induan and Olenekian.
The Middle Triassic Epoch has two Ages: Anisian and Ladinian.
The Late Triassic Epoch has three Ages: Carnian, Norian, and Rhaetian.
Frequent misspellings of geologic terms and Evolutionary periods of the Earth:
creataceous, cretaceus, cretacous, jurassique, jurasik, jurasic, jurossic, myscene, myocene, myoscene, phanaerozoic, triasic