Index
Astronomical and geological evidence indicates that the Universe is approximately 13,700 million years old, and our solar system is about 4,500 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 Orpheus or Theia, which accreted at a Lagrangian point 60° ahead or behind the Earth. A cataclysmic meteorite bombardment of the Moon and the Earth 3,900 million years ago is thought to have been caused by the debris of a planetary collision beyond the earth or by asteroids whose orbits were destabilized and were sent toward the inner solar system during the formation of planets beyond the Earth. 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 approximately 3,900 million years ago. The debris from this impact could have been responsible for the cataclysmic meteorite bombardment of the Earth and the Moon.
 Simplified model of the formation of the Moon |
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 joined 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.
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Precambrian Time (4,500 to 543 mya) |
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Hadean Eon (4500 to 3800 mya) |
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- 4500 mya: Formation of the Solar SystemSun was only 70% as bright as today. - 4450 mya: Formation of the moon - 3900 mya: Cataclysmic meteorite bombardment - Earth's atmosphere consisted of carbon dioxide, water vapor, methane, and ammonia. - Formation of carbonate minerals starts depleting atmospheric carbon dioxide. |
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| Archaean Eon (3800 to 2500 mya) |
- Surface of the Earth changed frommolten to solid rock. - Water started condensing in liquid form. - Earth day is 15 hours long - 3500 mya: Monocellular life started. First known oxygen-producing bacteria: cyanobacteria (blue-green algae) 
- 3000 mya: Atmosphere has 75% nitrogen,15% carbon dioxide. - Sun brightens to 80% of current level. - Oldest record of Earth's magnetic field. - 2500 mya: Oxygen catastrophe: Oxidation precipitates dissolved iron creating banded iron formations. Anaerobic organisms are poisoned by oxygen. |
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| Proterozoic Eon (2500 to 543 mya) |
Paleoproterozoic Era (2500 to 1600 mya) - Stable continents first appeared. - 2400 to 2100 mya: Huronian ice age - 2200 mya: Organisms with mitochondria capable of aerobic respiration appear. - 2023 mya: Meteor impact, 300 km crater Vredefort, South Africa [9] - 2000 mya: Solar luminosity is 85% of current level. - 1850 mya: Meteor impact, 250 km crater Sudbury, Ontario, Canada [9] - Abundant bacteria and archaeans. Mesoproterozoic Era (1600 to 900 mya) - Formation of the supercontinent Rodinia  
- Eukaryotic (nucleated) cells appear.- 1200 mya: Spore/gamete formation indicates origin of sexual reproduction. - Photosynthetic organisms proliferate. - Oxygen builds up in the atmosphere above 10%. - Formation of ozone layer starts blocking ultraviolet radiation from the sun. - 950 mya: Start of Stuartian-Varangian ice age Neoproterozoic Era (900 to 543 mya) - Length of day is 18 hours long. - Formation of the supercontinent Pannotia  Cryogenian Period (850 to 635 mya) - 750 mya: End of last magnetic reversal - 650 mya: Mass extinction of 70% of dominant sea plants due to global glaciation ("Snowball Earth" hypothesis). Vendian (Ediacaran) Period (635 to 543 mya) - 570 mya: End of Stuartian-Varangian ice age - Soft-bodied organisms developed First jellyfish. |
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Phanerozoic Eon (543 mya to present) |
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Paleozoic Era (543 to 251 mya) |
Cambrian Period (543 to 490 mya) - Most of the major groups of animals first appear Tommotian Epoch (530 to 527 mya) - Animals with shells appeared Solar brightness was 6% less than today. Ordovician Period (490 to 443 mya) 
- diverse marine invertebrates, such as trilobites,became common - First vertebrates appear. - 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 to 417 mya) - 420 mya: End of Andean-Saharan ice age. - Stabilization of the earth's climate - Coral reefs appeared - First fish with jaws - sharks - Spiders, centipedes, and plants appear on land Devonian Period (417 to 354 mya) - Ferns and seed-bearing plants (gymnosperms) appeared 
- First amphibians appear- Formation of the first forests - Wingless insects, and vertebrates appeared on land - Pannotia fragmented into Laurasia and Gondwana  - Atmospheric oxygen level is about 16% - 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. Carboniferous Period (354 to 299 mya) Mississippian Epoch (354 to 318 mya) 
- 350 mya: Beginning of Karoo ice age.- Large primitive trees develop - Oxygen levels increase - Vertebrates appear on land - First winged insects. - Seas covered parts of the continents - Animals laying amniote eggs appear (318 mya) Pennsylvanian Epoch (318 to 299 mya) - First reptiles - Atmospheric oxygen levels reach over 30% - 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) - Formation of the supercontinent Pangea  
- Conifers first appear- Earth is cold and dry - Sail-backed synapsids like Edaphosaurus and Dimetrodon appeared - 260 mya: End of Karoo ice age. - Period of great volcanism in Siberia releases large volume of gases (CO2, CH4, and H2S) [8] - Oxygen (O2) levels dropped from 30% to 12% Carbon dioxide (CO2) level ~2000 ppm - 251 mya: Great Permian-Triassic mass extinction Earth's worst mass extinction eliminated 90% of ocean dwellers, and 70% of land plants and animals. 
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Mesozoic Era (251 to 65 mya) |
Triassic Period (251 to 200 mya) - Break-up of Pangaea starts - Survivors of P-T extinction spread and recolonize - Sea urchins (Arkarua) appear (240 mya) - 235 mya: Evolutionary split between dinosaurs and lizards - First dinosaurs such as celophysis appear 
- Adelobasileus proto-mammal emerged (225 mya)- 214 mya: Meteor impact, 100 km crater Manicouagan, Quebec, Canada [9] - First evidence of mammals: Morganucodon (205 mya) - 201 mya: Mass extinction caused by oceanic anoxic event killed 20% of all marine families Jurassic Period (200 to 145 mya) - Earth is warm. There is no polar ice 
- Age of the dinosaurs- Giant herbivores and vicious carnivores dominate the land - North America separates from Africa (180 mya) - 167 mya: Meteor impact, 80 km crater Puchezh-Katunki, Russia [9] - 166 mya: Evolutionary split of monotremes from primitive mammals - First birds like Archaeopteryx appear (150 mya) - 148 mya: Evolutionary split between marsupial and eutherian mammals - 145 mya: Meteor impact, 70 km crater Morokweng, South Africa [9] Cretaceous Period (145 to 65 mya) 
- Period of Active Crust Plate Movements- Africa and India separate from Antarctica (125 mya) - Flowering plants (angiosperms) appeared - Crocodiles appeared (110 mya) - South America breaks away from Africa (105 mya) 
- Formation of the Atlantic Ocean- Modern mammals and birds developed - 100 mya: Earth's magnetic field is 3 times stronger than today. - 70 mya: Tyrannosaurus rex thrived 
- 65 mya: Meteor impact, 170 km craterChicxulub, Yucatan, Mexico [9] - Mass extinction of the dinosaurs |
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Cenozoic Era (65 mya to today) |
Tertiary Period (65 to 1.8 mya)  
Paleocene Epoch (65 to 54.8 mya) - Appearance of placental mammals - Formation of the Rocky Mountains - 55 mya: Major global warming episode CO2 concentration was 2000 ppm. Eocene Epoch (54.8 to 33.7 mya) - India meets Asia forming the Himalayas (50 mya) - Australia separates from Antarctica (45 mya) - Small modern mammals appear - 35.6 mya: Meteor impacts, 90 and 100 km craters Chesapeake Bay, Virginia, USA, and Popigai, Russia [9,10] 
Oligocene Epoch (33.7 to 23.8 mya)- 30 mya: Start of Pleistocene ice age - Appearance of many grasses - First elephants with trunks, camels, early horses - 27.8 mya: La Garita, Colorado supervolcanic eruption Miocene Epoch (23.8 to 5.3 mya) - African-Arabian plate joined to Asia - Warmer global climates - Drying of continental interiors - Forests give way to grasslands - 6 mya: Upright walking (bipedal) hominins appear Pliocene Epoch (5.3 to 1.8 mya) 
- Accumulation of ice at the poles- Spread of grasslands and savannas - Rise of long-legged grazing animals - Homo habilis appeared 2.4 mya - 2.1 mya: Yellowstone supervolcanic eruption - 2 mya: Tool-making humanoids emerge. Quaternary Period (1.8 mya to today) Pleistocene Epoch (1.8 mya to 10,000 yrs ago) - Homo erectus first moves out of Africa (1.7 mya) - 1.3 mya: Yellowstone supervolcanic eruption - Presence of large land mammals and birds - Yellowstone supervolcanic eruption 640,000 yrs ago - Episodes of global cooling, or glaciations 
- Hominids use controlled fires (300,000 yrs ago)- Neanderthal man spreads through Europe 230,000 yrs ago - Homo sapiens appeared 160,000 yrs ago. - Toba volcanic eruption (74,000 yrs ago) releases large volume of sulfur dioxide - Hominid ancestors reduced to about 10,000 individuals. - Tahoe glacial maximum (70,000 yrs ago) glaciers cover Canada and northern US 
- Oldest male ancestor of modern humans (60,000 yrs ago)[3] - Cro-Magnon man appeared 35,000 yrs ago. - Taupo supervolcanic eruption (26,500 yrs ago) in New Zealand - Tioga glacial maximum (22,000 yrs ago) sea level was 130 meters lower than today - 15,000 yrs ago: Land bridge between Alaska and Siberia allows human migration to America - 13,000 yrs ago: Extinction of megafauna such as the mammoth and sabretooth cat (Smilodon) - Fired pottery invented (12,000 yrs ago) - End of the Pleistocene ice age (11,600 yrs ago) Sea level rises by 91 meters (300 ft) Holocene Epoch (11,600 years ago to today) - Development of agriculture - Domestication of animals. - Metal smelting started (9,000 yrs ago) - Invention of the wheel (5,500 yrs ago)
- Pyramids of Giza (4,500 yrs ago) - Archimedes advances mathematics (2,230 yrs ago) - Industrialization (250 yrs ago) - Space travel (50 yrs ago) Sputnik orbits the earth in 1957. |
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Click Here to Take a Trip on the Geologic Time Machine |
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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 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 might have been responsible.
There is no doubt that human activities can have a substantial impact on the environment and
native species. The dodo, 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. The Dust Bowl
was a period of severe dust storms between 1930 and 1936 caused by deep plowing of the
top soil of the Great Plains which destroyed native grasses whose roots had protected the soil
from erosion. Soils that had been fertile
became incapable of sustaining crops after the top soil was blown away. The collapse of Cannery Row
was brought about by overfishing the costal waters of California. Production dropped from 235,000 tons of
fish in 1945 to only 15,000 tons of fish by 1948.
The Earth's near-term future
Human industrial activity has been generating 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.[2]
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.
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).[4] Satellite images by NASA show approximately a 20% reduction in the Earth's minimum ice cover between 1979 and 2003.[5] 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 end of this century.
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).[12] 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.[8]
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.[13] 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.
Glossary
Aeon - See Eon.
Archean, Archaean - An eon of geologic time extending from about 3800 to 2500 million years ago.
Derived from the Greek archaios meaning "ancient".
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 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 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 33.7 million years ago with four Ages:
Ypresian, Lutetian, Bartonian, and Priabonian.
Eon - A primary division of geologic time, 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 Stages.
Epoch - A division of geologic time shorter than a period.
Era - A division of geologic time 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".
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.
Mesozoic - An era of time during the Phanerozoic eon lasting from 251 million years ago to
65 million ago. Derived from the Greek mesos "middle" + zoe "life".
Miocene Epoch - An epoch from 23.8 to 5.3 million years ago with six Ages:
Aquitanian, Burgidalian, Langhian, Serravalian, Tortonian, and Messinaian.
Oligocene Epoch - An epoch from 33.7 to 23.8 million years ago with two Ages:
Rupelian and Chattian.
Paleocene, Palaeocene Epoch - An epoch from 65 to 54.8 million years ago with three Ages:
Danian, Selandian, and Thanetian.
Paleozoic, Palaeozoic - An era of geologic time lasting from 543 to 248 million years ago.
Derived from the Greek palai "long ago, far back" + zoe "life".
Period - A division of geologic time shorter than an era and longer than an epoch.
Phanerozoic - The most recent eon of geologic time beginning 543 million years ago and continuing to
the present. Derived from the Greek phaneros "visible" + zoe "life".
Pliocene Epoch - An epoch from 5.3 to 1.8 million years ago with two Ages:
Zanclean and Piacenzian.
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 543 million years ago. Derived from the Greek
proteros "earlier" + zoe "life".
Tertiary - A Period from 65 to 1.8 million years ago 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:
creataceous, cretaceus, cretacous, jurassique, jurasik, jurasic, jurossic, myscene, myocene, myoscene,
phanaerozoic, triasic
