History Of the Earth

By: Saagar Parikh

Some Words You Might Want to Know

• MYA: Million Years Ago• BYA: Billion Years Ago• TYA: Thousand Years Ago

The time periods or eras

Hadean 4.6-4 BYAThe name “Hadean” comes from Hades, the ancient Greek god of the underworld, in reference to the violent

conditions on Earth at the time. The planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The Hadean was the first of

three eons in Earths history. Earth didn’t look much like our home at this period.

Archean 4-2.5 BYAThe name “Archean” comes from the ancient Greek, meaning “beginning origin”. The Archean is the second

oldest of the three eons of Earth history. When the Archean began, the Earth's heat flow was nearly three times as high as it is today. The extra heat was the result of a mix of remnant heat from planetary growth, heat from the formation of the Earth's core, and heat produced by radioactive elements. The space objects that hit Earth in the Hadean contained small particles of water, and overtime the water collected and made oceans of water

in the Archean.

Proterozoic 2.500-541 MYAThe Proterozoic is a geological eon representing the time just before the spread of complex life on Earth. The

name “Proterozoic” comes from Greek and means “earlier life”. The first advanced single-celled, eukaryotes and multi-cellular life corresponds with the start of the accumulation of oxygen. The well-identified events of this

eon were the transition to an oxygenated atmosphere which caused several glaciations, including the hypothesized Snowball Earth (635 to 542 Ma) which is characterized by the evolution of abundant soft-bodied

multicellular organisms. The oceans at the time were very shallow and widespread.

Paleozoic Era

541-252 MYAThe start of life

Cambrian 541-485 MYAThe Cambrian period was established by Adam Sedgwick, who named it after Cambria, the Latin name

for Wales, where Britain's Cambrian rocks are best exposed. The Cambrian Period marked a profound change in life on Earth; prior to the Cambrian, living organisms on the whole were small, unicellular and simple. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – therefore readily fossilized

organisms became common. While diverse life forms prospered in the oceans, the land was comparatively barren – with nothing more complex than a bacterial soil crust and a few mollusks that emerged to browse on

the microscopic biofilm. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas lined the margins of several continents created during the breakup of the supercontinent

Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.

Ordovician 485-443 MYAThe Ordovician was named after the Celtic tribe of the Ordovices. Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass

extinction. Invertebrates, mainly mollusks and arthropods, dominated the oceans. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to appear on land. Sea levels were high during the Ordovician. In the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide into the atmosphere, turning the planet into a hothouse. These volcanic island arcs eventually collided with proto

North America to form the Appalachian mountains. By the end of the Late Ordovician these volcanic emissions had stopped. Gondwana had by that time neared or approached the pole and was largely glaciated.

Colonization of land was limited to shorelines.

Silurian 443-419 MYA The Silurian was named after a Celtic tribe of Wales, the Silures. The base of the Silurian is set at a

major extinction event when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. Life also began to appear on land in the form

of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines, and also in the form of small terrestrial arthropods. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian. During this period, the Earth entered a long, warm greenhouse phase, and warm shallow seas

covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of the Silurian.

Devonian 419-359 MYAThe period is named after Devon, a county in southwestern England, where a controversial argument in the

1830s over the age and structure of the rocks found distributed throughout the county. The Devonian period experienced the first significant adaptive energy of terrestrial life. Free-sporing vascular plants began to spread

across dry land, forming widespread forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached extensive diversity during this time, leading the Devonian to often be nicknamed the "Age of Fish". The first ray-finned and lobe-

finned bony fish appeared. The ancestors of tetrapods began adapting to walking on land, their strong pectoral and pelvic fins gradually evolving into legs, and in the oceans, simple sharks became more numerous. The

Devonian was a relatively warm period, and probably lacked any glaciers.

Mississippian 359-323 MYA The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley. The

Mississippian was a period of marine ingression in the Northern Hemisphere: the ocean stood so high that only the Fennoscandia Shield and the Laurentian Shield stood above sea level. The cratons were surrounded by

extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas. Amphibians started to take over the land, but had to stay near the water, and large

bugs started to evolve because of the high amounts of oxygen in the air.

PENNSYLVANIAN 323-299 MYAThe Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-productive beds of this age are widespread. Amphibians were diverse and common; some were several meters long as adults. The collapse of the rainforest ecology in the mid Pennsylvanian removed many amphibian species that did not survive as well in the cooler, drier conditions. Reptiles, however, thrived due to specific key adaptations. One of the greatest evolutionary revolutions of the Carboniferous was the egg with a shell (amniote egg), which allowed for the

further use of the land by certain reptiles.

Permian 299-252 MYAThe Permian is named after the ancient kingdom of Permia. The extensive rainforests of

the Pennsylvanian had disappeared, leaving behind vast regions of arid desert within the continental interior.

Amniotes, who could better cope with these drier conditions, rose to dominance in the place of their amphibian ancestors. During this time, amniotes grew to enormous sizes. The Permian Period (along with the Paleozoic Era) ended with the largest mass extinction in Earth's history, in which nearly 90% of marine species

and 70% of terrestrial species died out.

MESOZOIC ERA

252-65 MYAWHEN DINOSAURS RULED THE LAND

Triassic 252- 201 MYA The Triassic was named after the three distinct rock layers (tri meaning "three") that are found

throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias. A specialized subgroup of archosaurs, (dinosaurs), first

appeared in the Late Triassic but did not become dominant until the succeeding Jurassic. The first true mammals, themselves a specialized subgroup of therapsids also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who like the dinosaurs were a specialized subgroup of archosaurs. The global climate during the Triassic was mostly hot and dry. The end of the period was marked by yet another

major mass extinction, the Triassic-Jurassic extinction event, wiping out many groups and allowing dinosaurs to accept dominance in the Jurassic.

Jurassic 201-145 MYAThe Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the

period were first identified. By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush

rainforests. On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The

first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including basic placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were

inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The Jurassic was a golden age for the large herbivorous dinosaurs known as the sauropods that roamed the land late in the period; their mainstays were either the prairies of ferns, palm-like cycads and

bennettitales, or the higher coniferous growth, according to their adaptations. They were preyed upon by large theropods.

Cretaceous 145-66 MYAThe Cretaceous was named from the Latin "creta" (chalk), usually abbreviated K for its German translation

“Kreide” (chalk). The Cretaceous was a period with a relatively warm climate, resulting in high sea levels and creating numerous, shallow, inland seas These oceans and seas were populated with now-extinct marine

reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. At the same time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a large mass

extinction, the Cretaceous–Paleogene extinction event, in which many groups, including dinosaurs, pterosaurs and large marine reptiles, died out.

Cenozoic Era

65 Mya-PresentRise of the mammals

Paleocene 65-56 MYAThe name "Paleocene" comes from Greek and refers to the "old(er)" "new“ fauna that arose during the epoch.

It started with the mass extinction event at the end of the Cretaceous, known as the Cretaceous-Paleogene boundary. This was a time marked by the death of the dinosaurs, giant marine reptiles and much

other animals and plants. The die-off of the dinosaurs left unfilled ecological slots worldwide. It ended with the Paleocene-Eocene Thermal Maximum. This was a geologically brief pause characterized by extreme

changes in climate and carbon cycling. Mammals had first appeared in the Triassic, evolving from advanced cynodonts, and developed alongside the dinosaurs, untouched by the larger and more

famous Mesozoic animals: in the insect-rich forest underbrush and high up in the trees. These smaller mammals (as well as birds, reptiles, amphibians, and insects) survived the mass extinction at the end of the

Cretaceous which wiped out the, and mammals differentiated and spread throughout the world.

Eocene 56-33.9 MYAThe name Eocene comes from the Greek (eos, dawn) and (kainos, new) and refers to the "dawn" of modern ('new')creatures that appeared during the epoch. Among terrestrial vertebrates, the start of the Eocene is

marked by the appearance of two new groups of animals: the perissodactyls, or odd-toed ungulates, and the artiodactyls, or even-toed ungulates. The perissodactyls include the horses, rhinoceroses, and tapirs; among the artiodactyls are the deer, cattle, and sheep. Artiodactyls, rare during the early Eocene, became abundant

later in the period. The Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era and ends in an icehouse climate. The Eocene oceans were warm and teeming with fish and other sea life. The first carcharinid sharks evolved, as did early marine mammals,

including Basilosaurus, an early species of whale that is thought to be descended from land animals that existed earlier in the Eocene, the hoofed predators called mesonychids. The first sirenians, relatives of

the elephants, also evolved at this time.

Oligocene 33.9-23 MYAThe name Oligocene comes from the Greek (oligos, few) and (kainos, new), and refers to the scarcity of

additional modern mammalian species of animals after a burst of evolution during the Eocene. Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleogene. Aquatic animals

became fairly modern, as did land-dwelling vertebrate on the northern continents. This was probably more as a result of older forms dying out than as a result of more modern forms evolving. Many groups, such

as horses, entelodonts, rhinoceroses, oreodonts, and camels, became more able to run during this time, adapting to the plains that were spreading as the Eocene rainforests retreated to the Equator. South America was isolated from the other continents and evolved a quite distinct creatures during the Oligocene. The South

American continent became home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchian (longer legged, taller standing) crocodiles, terror birds, and

carnivorous marsupials remained the dominant predators.

Miocene 23-5.3 MYAThe name Miocene comes from the Greek (meiōn, “less”) and (kainos, “new”) and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The apes arose and diversified during the Miocene, becoming widespread in the Old World. By the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path. As in the Oligocene before it, grasslands continued to expand and forests to shrink in extent. In the Miocene seas, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems. The plants and animals of the Miocene were fairly modern. Mammals and birds were well-established. Whales, seals, and kelp spread.

Pliocene 5.3-2.6 MYAPliocene comes from the Greek words (pleion, "more") and (kainos, "new") and means roughly "continuation of the recent", referring to the essentially modern marine mollusks. The change to a cooler, dry, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests grew, coniferous forests and tundra covered much of the North, and grasslands spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs, deserts appeared in Asia and Africa. The first recognizable hominins, the australopithecines, appeared in the Pliocene. In North America, rodents, large mastodons and gomphotheres, and opossums continued successfully, while hoofed animals declined, with camel, deer and horse all seeing populations recede. Rhinos, three toed horses, oreodonts, protoceratids, and chalicotheres went extinct. Borophag, dogs and Agriotherium went extinct, but other carnivores including the weasel family diversified, and dogs and fast-running hunting bears did well. Ground sloths, huge glyptodonts, and armadillos came north with the formation of the Isthmus of Panama.

Pleistocene 2.6 mya-11000 TYAThe word Pleistocene comes from the Greek words ("Most New" or "Newest"). Pleistocene climate was marked by repeated ice ages in which continental glaciers pushed to the 40th parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometers in North America, and several hundred in Eurasia. The average annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F). The severe climatic changes during the ice age had major impacts on the plants and animals. With each advance of the ice, large areas of the continents became totally depopulated, and plants and animals retreating southward in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major extinction event of large mammals (megafauna), which included, mammoths, mastodons saber-toothed cats, glyptodonts, ground sloths, Irish elk, cave bears, and short-faced bears, began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice, migratory birds, and swifter animals like whitetail deer had replaced the megafauna and migrated north. The extinctions were especially severe in North America where native horses and camels were eliminated. Scientific evidence indicates that humans evolved into their present form during the Pleistocene.

Holocene 11 tya-presentIts name comes the from Greek words (holos, whole or entire) and (kainos, new), meaning "entirely recent". The Holocene also encompasses the growth and impacts of the human species worldwide, including all its written history, development of major civilizations, and overall significant transition toward urban living in the present. Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species.

“Age Of Man”