the+story+of+life+on+Earth


 * || = Earth in the Beginning = ||  ||   ||
 * = Republished from the pages of [|National Geographic magazine]

Written by Tim Appenzeller

December 2006 The early Earth was a vision of hell, all scalding rock and choking fumes. Since then, its surface has cooled, continents have drifted, mountains have risen and eroded, and life has emerged, benign and green. Nearly all traces of the planet as it was have been wiped away. But from clues in the oldest rocks, deepest magmas, and even the cratered face of the moon, scientists have traced the planet's beginnings. As those early days have come into focus, so have the rare scenes, found today in some of Earth's harshest places, that recall its ancient self. || || Artwork depicting one theory of how gas-giant planets form ||   || THIS ARTICLE IS FROM

[|National Geographic Magazine]


Its birth pangs began some 4.6 billion years ago as rock and ice particles swirling around the young sun collided and merged, snowballing to produce ever larger planetary building blocks. In violent pileups, they smashed together to create planets, including the infant Earth. In the turmoil, another body, as big as Mars, struck our planet with the energy of trillions of atomic bombs, enough to melt it all the way through. Most of the impactor was swallowed up in the bottomless magma ocean it created. But the collision also flung a small world's worth of vaporized rock into orbit. Debris quickly gathered itself into a ball, and since then Earth history has unfolded beneath the blank stare of the moon. After the moon's fiery birth, the Earth's surface cooled. Even so, our planet remained an alien world for the next 700 million years; scientists call this time the Hadean, after the Greek underworld. Rafts of solid rock drifted in the magma like dark ice floes. Gases hissed from the cooling rock—carbon dioxide, nitrogen, water vapor, and others—enveloping the planet in a scalding atmosphere devoid of oxygen. As the temperature dropped further, the steam condensed into rain that tell in primordial monsoons and filled the ocean basins. These first oceans may have been short-lived. Space rubble left over from the birth of the planets—chunks of rock tens to hundreds of miles across—bombarded Earth throughout the Hadean. The greatest impacts might have boiled the oceans away, forcing the process of cooling and condensation to begin again. By 3.8 billion years ago the impacts relented. Liquid water could persist. About that time, perhaps in the oceans, lifeless chemical reactions crossed a threshold, producing molecules complex enough to reproduce themselves and evolve toward greater complexity. Life was on a road that led, as early as 3.5 billion years ago, to single-celled, blue-green cyanobacteria that flourished in the sunlit parts of the oceans. By the trillions, these microscopic organisms transformed the planet. They captured the energy of the sun to make food, releasing oxygen as a waste product. Little by little they turned the atmosphere into breathable air, opening the way to the diversity of life that followed. Those days are long gone, but the processes that turned our planet from a hell to a habitable world are still on view today. Primordial heat left over from the planet's formation still bursts out in volcanic eruptions, spilling lava that exudes gases like the young, cooling Earth. In the planet's harshest environments today, cyanobacteria reign as they have for billions of years. And each time a plant gains a toehold on newly cooled lava, the victory of life over lifeless rock—won so long ago on the young Earth—is affirmed again

By [|Eric McLamb], September 10, 2011 Earth is the only planet we know of that can support life. This is an amazing fact, considering that it is made out of the same matter as other planets in our solar system, was formed at the same time and through the same processes as every other planet, and gets its energy from the sun. To a universal traveler, Earth may seem to be a harmless little planet in the far reaches of one of billions of spiral galaxies in the universe. It has an average size star of average brightness and is joined by seven other planets — which support no known life forms — in its solar system. While this may be fitting for a passage from [|The Hitchhikers Guide to the Galaxy], by Douglas Adams, in the grand scheme of the universe, it would be a fairly accurate description. However, Earth is a planet teeming with vitality and is home to billions of plants and animals that share a common evolutionary track. How and why did we get here? What processes had to take place for this to happen? And where do we go from here? The fact is, no one has been able to come close to knowing exactly what led to the origins of life, and we may never know. After 5 billion years of Earth’s formation and evolution, the evidence may have been lost. But scientists have made significant progress in understanding what chemical processes that may have led to the origins of life. There are many theories, but most have the same general perspective of how things came to be the way they are. Following is an account of life’s beginnings based on some of the leading research and theories related to the subject, and of course, [|fossil records]dating back as far as 3.5 billion years ago.

Earth’s Beginnings
The solar system was created from gas clouds and dust that remained from the Sun's formation some 6-7 billion years ago. This material contained only about .2% of the solar system's mass with the Sun holding the rest. (NASA graphic, by N. A. Cabrol) Earth began to form over [|4.6 billion years ago] from the same cloud of gas (mostly hydrogen and helium) and interstellar dust that formed our[|sun], the rest of the solar system and even our galaxy. In fact, Earth is still forming and cooling from the galactic implosion that created the other stars and planetary systems in our galaxy. This process began about 13.6 billion years ago when the [|Milky Way Galaxy] began to form. As our solar system began to come together, the sun formed within a cloud of dust and gas that continued to shrink in upon itself by its own gravitational forces. This caused it to undergo the fusion process and give off light, heat and other radiation. During this process, the remaining clouds of gas and dust that surrounded the sun began to form into smaller lumps called [|planetesimals], which eventually formed into the planets we know today. A large number of small objects, called planetesimals, began to form around the Sun early in the formation of the solar system. These objects were the building blocks for the planets that exist today. (NASA graphic, by N. A. Cabrol.) The Earth went through a period of catastrophic and intense formation during its earliest beginnings 4.6-4.4 billion years ago. By 3.8 to 4.1 billion years ago, Earth had become a planet with an atmosphere (not like our atmosphere today) and an ocean. This period of Earth’s formation is referred to as the [|pre-Cambrian Period]. The pre-Cambrian is divided into three parts: the[|Hadean], [|Archean] and [|Proterozoic]Periods.

Pre-Cambrian Period
The Earth formed under so much heat and pressure that it formed as a molten planet. For nearly the first billion years of formation (4.5 to 3.8 billion years ago) — called the Hadean Period (or hellish period) — Earth was bombarded continuously by the remnants of the dust and debris — like asteroids, meteors and comets — until it formed into a solid sphere, pulled into orbit around the sun and began to cool down. Earth's early atmosphere most likely resembled that of Jupiter's atmosphere, which contains hydrogen, helium, methane and ammonia, and is poisonous to humans. (Photo: NASA, from Voyager 1) As Earth began to take solid form, it had no free oxygen in its atmosphere. It was so hot that the water droplets in its atmosphere could not settle to form surface water or ice. Its [|first atmosphere] was also so poisonous, comprised of helium and hydrogen, that nothing would have been able to survive. [|Earth’s second atmosphere] was formed mostly from the out gassing of such volatile compounds as water vapor, carbon monoxide, methane, ammonia, nitrogen, carbon dioxide, nitrogen, hydrochloric acid and sulfur produced by the constant volcanic eruptions that besieged the Earth. It had no free oxygen. About 4.1 billion years ago, the Earth’s surface — or crust — began to cool and stabilize, creating the solid surface with its rocky terrain. Clouds formed as the Earth began to cool, producing enormous volumes of rainwater that formed the oceans. For the next 1.3 billion years (3.8 to 2.5 billion years ago), the Archean Period, first life began to appear and the world’s landmasses began to form. [|Earth’s initial life forms] were bacteria, which could survive in the highly toxic atmosphere that existed during this time. Toward the end of the [|Archean Period] and at the beginning of the [|Proterozoic Period], about 2.5 billion years ago, oxygen-forming photosynthesis began to occur. The first fossils were a type of[| blue-green algae] that could photosynthesize. Earth's atmosphere was first supplied by the gasses expelled from the massive volcanic eruptions of the Hadean Era. These gases were so poisonous, and the world was so hot, that nothing could survive. As the planet began to cool, its surface solidified as a rocky terrain, much like Mars' surface (center photo) and the oceans began to form as the water vapor condensed into rain. First life came from the oceans. Source: NASA, NWS Some of the most exciting events in Earth’s history and life occurred during this time, which spanned about two billion years until about 550 million years ago. The continents began to form and stabilize, creating the supercontinent [|Rodinia] about 1.2 billion years ago. Although Rodinia is composed of some of the same land fragments as the more popular supercontinent, [|Pangea], they are two different supercontinents. Pangea formed some 225 million years ago and would evolve into the seven continents we know today. Free oxygen began to build up around the middle of the [|Proterozoic Period] — around 1.8 billion years ago — and made way for the emergence of life as we know it today. This increased oxygen created conditions that would not allow most of the existing life to survive and thus made way for the more oxygen-dependent life forms. By the end of the Proterozoic Period, Earth was well along in its evolutionary processes leading to our current period, the [|Holocene Period], or [|Anthropocene Period], also known as the Age of Man. Thus, about 525 million years ago, the [|Cambrian Period] began. During this period, life “exploded,” developing almost all of the major groups of plants and animals in a relatively short time. It ended with the massive extinction of most of the existing species about 500 million years ago, making room for the future appearance and evolution of new plant and animal species. About 498 million years later — 2.2 million years ago — the first modern human species emerged. (Compiled with the assistance of a broad range of science and research resources and review by Dr. Jack C. Hall, Director of Environmental Studies, UNC Wilmington)

Did You Know?
The first modern human being was called [|homo habilis], the first of the[| homo genus]. This species developed stone tools for use in daily life. Homo habilis means “Handy Man.” He existed from about 2.2 to 1.5 million years ago. There are earlier species related to modern man, called [|hominids]. The images show the skull shape and probable appearance of homo habilis. The [|Pre-Cambrian Period] — accounts for about 90 percent of Earth’s history. It lasted for about four billion years until about 550 million years ago. About 70 percent of the world’s land masses were created in the [|Archean Era], between 3.8 and 2.5 million years ago. Rodinia, widely recognized as the first supercontinent, formed during the [|Proterozoic Era], about 2.5 billion years ago. It is believed that the oldest human family member was discovered in Ethiopia and lived 4.4 million years.

 Geologic and Biological Timeline of the Earth Astronomical and geological evidence indicates that the Universe is approximately 13,820 million years old[42], 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.[20]
 *  [|Timeline]
 *  [|Time Machine]
 *  [|Atmosphere]
 *  [|Impacts]
 *  [|Aïr Massif]
 *  [|Mare Moscoviense]
 *  [|Lunar Maria]
 *  [|Moon Map]
 *  [|Geology Glossary]
 *  [|Evolution]

Simplified model of the formation of the Moon

Approximately 4,000 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 Pangea. The break up of Pangea, which still goes on today, has contributed to the formation of the Atlantic Ocean.

(4567 to 542 mya) || - 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.[33] Earth day is 7 hours long[34] - 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.[30] - 4280 mya: Water started condensing in liquid form. - 3900 mya: Cataclysmic meteorite bombardment. The Moon is 282,000 km from Earth.[34] Earth day is 14.4 hours long[34] - 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. || - 4000 mya: The Earth's crust cooled and solidified. - Atmospheric pressure ranged from 100 to 10 bar. - Earth day is 15 hours long - 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. - 3000 mya: Atmosphere has 75% nitrogen, 15% carbon dioxide. - Sun brightens to 80% of current level. - 2900 mya: Pongola glaciation occurred. - 2800 mya: Break up of supercontinent Vaalbara. - Oldest record of Earth's magnetic field. - 2700 mya: Supercontinent Kenorland formed. - Photosynthetic organisms proliferate. || - 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.[14] Anaerobic organisms are poisoned by oxygen. - 2400 mya: Start of Huronian ice age - 2200 mya: Organisms with mitochondria capable of aerobic respiration appear. - 2100 mya: End of Huronian ice age - Intensive orogeny (mountain development) - 2023 mya: Meteor impact, 300 km crater Vredefort, South Africa [9] - 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 [9] - Complex single-celled life appeared. - Abundant bacteria and archaeans. - Photosynthetic organisms continue to proliferate. - Oxygen builds up in the atmosphere above 10%. - Formation of ozone layer starts blocking ultraviolet radiation from the sun. - 1600 mya: Eukaryotic (nucleated) cells appear. Origin of ancestor of all animals, plants and fungi - Green (Chlorobionta) and red (Rhodophyta) algae abound. - 1200 mya: Spore/gamete formation indicates origin of sexual reproduction.[36] - 1100 mya: Formation of the supercontinent Rodinia - 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.[31] - 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.[31] - 600 mya: Earth day is 20.7 hours long.[35] - 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) || - Abundance of multicellular life. - Most of the major groups of animals first appear - 510 mya: Vertebrates appeared in the ocean. Solar brightness was 6% less than today. - diverse marine invertebrates, such as trilobites, became common - 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. - 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 - 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 Woodleigh, Australia (Lower Carboniferous) - 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) (Upper Carboniferous) - 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.[31] - Giant arthropods populate the land - Transgression and regression of the seas caused by glaciation - Deposits of coal form in Europe, Asia, and North America - 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 [26] - 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 was about 2000 ppm Temperatures reach 50-60°C on land, and 40°C at the sea-surface.[37] Earth's worst mass extinction eliminated 90% of ocean dwellers, and 70% of land plants and animals. || - 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 [9] - 205 mya: First evidence of mammals: //Morganucodon// - 201 mya: Volcanism in Central Atlantic Magmatic Province[38] * Mass extinction killed 20% of all marine families - 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 [9] - 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 [9] - Period of Active Crust Plate Movements - 133 mya: Meteor impact, 55 km crater Tookoonooka, Australia [9] - 125 mya: Africa and India separate from Antarctica - Flowering plants (angiosperms) appeared //Montsechia vidalli// was one of the first angiosperms. - 120 mya: Global warming event starts Carbon dioxide levels were 550 to 590 ppm [27] - Proliferation of single-cell organisms (diatoms, dinoflagellates, and calcareous nannoplankton) changed ocean composition. - 116 mya: First birds with beaks without teeth. - 110 mya: Crocodiles appeared - Snakes evolved during the mid-Cretaceous - 105 mya: South America breaks away from Africa - Formation of the Atlantic Ocean - Earth has no polar ice - 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) - 85 mya: Australia starts to separate from Antarctica - 70 mya: Meteor impact, 65 km crater Kara, Russia [9] Caution: Do not poke T. rex - 68 mya: //Tyrannosaurus rex// thrived - 67.5 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 [9] - * Mass extinction of 80-90% of marine species and 85% of land species, including the dinosaurs. || - 63 mya: End of Deccan Traps volcanic eruptions in India - Flowering plants become widespread. - 70% of new bird lineages evolved within five million years after the extinction of the dinosaurs. - Social insects achieve ecological dominance. - Appearance of placental mammals (marsupials, insectivores, lemuroids, creodonts) - 60 mya: Earliest known ungulate (hoofed mammal) - Formation of the Rocky Mountains - 55.8 mya: Major global warming episode (PETM)[39] North Pole temperature averaged 23°C (73.4°F), CO2 concentration was 2000 ppm. - 50 mya: India meets Asia forming the Himalayas - 45 mya: Earth day is 24 hours long. The Moon is 378,000 km from Earth.[32] - Modern mammals appear rhinoceros, camels, early horses and lemur-like primates appear - 35.6 mya: Meteor impacts, 90 and 100 km craters Chesapeake Bay, Virginia, USA, and Popigai, Russia [9,10] - Global temperature dropped 10°C during the Eocene. - 34 mya: Global cooling creates permanent Antarctic ice sheet [21] - 30 mya: Australia and South America separate from Antarctica - Appearance of many grasses - First elephants with trunks - 27.8 mya: La Garita, Colorado supervolcanic eruption
 * ~ Precambrian Time
 * ||||= **Hadean Eon** (4567 to 4000 mya) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/hadean-eon.gif width="20" height="234" caption="Hadean Eon"]] || - 4650 mya: Formation of [|chondrules] in the Solar Nebula
 * ||||= **Archean Eon** (4000 to 2500 mya) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/archean-eon.gif width="20" height="238" caption="Archean Eon"]] || **Eoarchean Era** (4000 to 3600 mya)
 * Paleoarchean Era** (3600 to 3200 mya)
 * Mesoarchean Era** (3200 to 2800 mya)
 * Neoarchean Era** (2800 to 2500 mya)
 * ||||= **Proterozoic Eon** (2500 to 542 mya) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/proterozoic-eon.gif width="20" height="258" caption="Proterozoic Eon"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/proterozoic-eon.gif width="20" height="258" caption="Proterozoic Eon"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/proterozoic-eon.gif width="20" height="258" caption="Proterozoic Eon"]] || **Paleoproterozoic Era** (2500 to 1600 mya)
 * Siderian Period** (2500 to 2300 mya)
 * Rhyacian Period** (2300 to 2050 mya)
 * Orosirian Period** (2050 to 1800 mya)
 * Statherian Period** (1800 to 1600 mya)
 * Mesoproterozoic Era** (1600 to 1000 mya)
 * Calymmian Period** (1600 to 1400 mya)
 * Ectasian Period** (1400 to 1200 mya)
 * Stenian Period** (1200 to 1000 mya)
 * Neoproterozoic Era** (1000 to 542 mya)
 * Tonian Period** (1000 to 850 mya)
 * Cryogenian Period** (850 to 630 mya)
 * Ediacaran (Vendian) Period** (630 to 542 mya)
 * ~ **Phanerozoic Eon**
 * ~ **Phanerozoic Eon**
 * ||||= **Paleozoic Era** (542 to 251 mya) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/paleozoic-era.gif width="20" height="241" caption="Paleozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/paleozoic-era.gif width="20" height="241" caption="Paleozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/paleozoic-era.gif width="20" height="241" caption="Paleozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/paleozoic-era.gif width="20" height="241" caption="Paleozoic Era"]] || **Cambrian Period** (542 to 488.3 mya)
 * Tommotian Stage** (534 to 530 mya)
 * Ordovician Period** (488.3 to 443.7 mya)
 * Silurian Period** (443.7 to 416 mya)
 * Devonian Period** (416 to 359.2 mya)
 * Carboniferous Period** (359.2 to 299 mya)
 * Mississippian Epoch** (359.2 to 318.1 mya)
 * Pennsylvanian Epoch** (318.1 to 299 mya)
 * Permian Period** (299 to 251 mya)
 * ||||= **Mesozoic Era** (251 to 65.5 mya) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/mesozoic-era.gif width="20" height="232" caption="Mesozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/mesozoic-era.gif width="20" height="232" caption="Mesozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/mesozoic-era.gif width="20" height="232" caption="Mesozoic Era"]] || **Triassic Period** (251 to 199.6 mya)
 * Jurassic Period** (199.6 to 145.5 mya)
 * Cretaceous Period** (145.5 to 65.5 mya)
 * ||||= **Cenozoic Era** (65.5 mya to today) ||
 * ||= [[image:http://www.scientificpsychic.com/etc/timeline/cenozoic-era.gif width="20" height="248" caption="Cenozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/cenozoic-era.gif width="20" height="248" caption="Cenozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/cenozoic-era.gif width="20" height="248" caption="Cenozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/cenozoic-era.gif width="20" height="248" caption="Cenozoic Era"]][[image:http://www.scientificpsychic.com/etc/timeline/spacer.gif width="20" height="250"]][[image:http://www.scientificpsychic.com/etc/timeline/cenozoic-era.gif width="20" height="248" caption="Cenozoic Era"]] || **Paleogene Period** (65.5 to 23.03 mya)
 * Tertiary Period** (65.5 to 2.58 mya)
 * Paleocene Epoch** (65.5 to 55.8 mya)
 * Eocene Epoch** (55.8 to 33.9 mya)
 * Oligocene Epoch** (33.9 to 23.03 mya)

- African-Arabian plate joined to Asia - 21 to 14 mya: Miocene warming period - 14 mya: Circum-polar ocean circulation builds up Antarctic ice cap. - 14 to 6 mya: Global temperature drops by 4°C. - First raccoons appear. - Drying of continental interiors - Forests give way to grasslands - 6 mya: Upright walking (bipedal) hominins appear - 4.4 mya: Appearance of //Ardipithecus//, an early hominin genus. - 4 mya: North and South America join at the Isthmus of Panama. Animals and plants cross the new land bridge. Ocean currents change in the newly isolated Atlantic Ocean. - 3.9 mya: Appearance of //Australopithecus//, genus of hominids. - 3.7 mya: //Australopithecus// hominids inhabit Eastern and Northern Africa. - 3 mya: Formation of Arctic ice cap. - Accumulation of ice at the poles - Climate became cooler and drier. - Spread of grasslands and savannas - Rise of long-legged grazing animals - Several major episodes of global cooling, or glaciations - 2.4 mya: //Homo habilis// appeared - 2.1 mya: Yellowstone supervolcanic eruption - 2 mya: Tool-making humanoids emerge. Beginning of the Stone Age. - 1.7 mya: //Homo erectus// first moves out of Africa - 1.3 mya: Yellowstone supervolcanic eruption - 1.3 mya to 820,000 yrs ago: Sherwin Glaciation - Presence of large land mammals and birds - 790,000 yrs ago: First use of fire by hominds[40] - 700,000 yrs ago: Human and Neanderthal lineages start to diverge genetically. - 680,000 to 620,000 yrs ago: Günz/Nebraskan glacial period - 640,000 yrs ago: Yellowstone supervolcanic eruption - 530,000 yrs ago: [|Development of speech in //Homo Heidelbergensis//] [15] - 455,000 to 300,000 yrs ago: Mindel/Kansan glacial period - 400,000 yrs ago: Hominids hunt with wooden spears and use stone cutting tools. - 370,000 yrs ago: Human ancestors and Neanderthals are fully separate populations. - 300,000 yrs ago: Hominids routinely use controlled fires - 230,000 yrs ago: Neanderthal man spreads through Europe - 200,000 to 130,000 yrs ago: Riss/Illinoian glacial period - 160,000 yrs ago: //Homo sapiens// appeared. Origin of human female lineage.[3] - 125,000 yrs ago: Eemian stage or Riss/Würm interglacial period. Hardwood forests grew above the Arctic Circle. Melting ice sheets increased sea level by 6 meters (20 feet) - 110,000 yrs ago: Start of Würm/Wisconsin glacial period - 105,000 yrs ago: Stone age humans forage for grass seeds such as sorghum. - 80,000 yrs ago: Non-African humans interbreed with Neanderthals[28] - 74,000 yrs ago: Toba volcanic eruption releases large volume of sulfur dioxide - 71,000 yrs ago: Invention of the bow and arrow.[41] - 70,000 yrs ago: //Tahoe// glacial maximum glaciers cover Canada and northern US. - 55,000 yrs ago: Humans colonize Australia - 46,000 yrs ago: Australia becomes arid, bush fires destroy habitat, and megafauna die off. - 40,000 yrs ago: //Cro-Magnon// man appeared in Europe. - 28,000 yrs ago: Neanderthals disappear from fossil record.[29] - 26,500 yrs ago: Taupo supervolcanic eruption in New Zealand. - 22,000 yrs ago: //Tioga// glacial maximum sea level was 130 meters lower than today. - 20,000 yrs ago: Invention of fired ceramic pottery. - 19,000 yrs ago: Antarctic sea ice starts melting.[22] - 15,000 yrs ago: Bering land bridge between Alaska and Siberia allows human migration to America. - 12,900 yrs ago: [|Comet impact by Great Lakes] [23, 24, 25] Extinction of American megafauna such as the mammoth and sabretooth cat (//Smilodon//), as well as the end of Clovis culture - 11,400 yrs ago: End of Würm/Wisconsin glacial period. Sea level rises by 91 meters (300 ft) - Development of agriculture - Domestication of animals. - 9,000 yrs ago: Metal smelting started - 5,500 yrs ago: Invention of the wheel - 5,300 yrs ago: The Bronze Age - 5,000 yrs ago: Development of writing - 4,500 yrs ago: Pyramids of Giza - 3,300 yrs ago: The Iron Age - 2,240 yrs ago: Archimedes develops formula for the volume of a sphere. - 2015 yrs ago: Start of the Common Era (CE) - 1760 CE: The Industrial Revolution - 1945 CE: Atomic age - First nuclear explosion - 1957 CE: Space age - Launch of Sputnik Artificial satellite orbits the Earth. - 1969 CE: Humans walk on the surface of the Moon. ||
 * Neogene Period** (23.03 mya to today)
 * Miocene Epoch** (23.03 to 5.3 mya)
 * Pliocene Epoch** (5.3 to 2.58 mya)
 * Quaternary Period** (2.58 mya to today)
 * Pleistocene Epoch** (2.58 mya to 11,400 yrs ago)
 * Holocene Epoch** (11,400 years ago to today)

[|a Trip on the Geologic Time Machine] ||= || 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**
 * = [|Click Here to Take]

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.[25] 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.[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. 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).[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 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).[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] Florida New Orleans

**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. (my = millions of years) +1500 my: Sun is about 6000 million years old and 15% brighter than today. +2000 my: Milky Way Galaxy starts colliding with Andromeda Galaxy.[13] +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.[18] 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. || ** Glossary **
 * ~ Earth's Long-Term Future ||
 * || +200 years: Possible global warming event caused by anthropogenic carbon dioxide (CO2)[8]

**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.