History of Our Earth - Anniversary Special Post

The history of Earth concerns the development of the planet Earth from its formation to the present day. The age of Earth is approximately one-third of the age of the universe. Earth formed around 4.54 billion years ago. Volcanic outgassing probably created the primordial atmosphere and then the ocean; but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans.

Volcanism

Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. A "giant impact" collision with a planet-sized body is thought to have been responsible for forming the Moon. Over time, the Earth cooled, causing the formation of a solid crust, and allowing liquid water to exist on the surface.


Life of our Earth is divided into 4 ages or eons(units are in Million Years Ago) . 

• Hadean(4,540-4,000 MYA) : The Earth is formed out of debris around the solar protoplanetary disk. There is no life. Temperatures are extremely hot, with frequent volcanic activity and hellish environments. The atmosphere is nebular. Possible early oceans or bodies of liquid water. The moon is formed around this time, probably due to a protoplanet's collision into Earth. 
• Archean(4,000-2,500 MYA) : Prokaryote life, the first form of life, emerges at the very beginning of this eon, in a proccess known as abiogenesis. The continents of Ur and Vaalbara may have been formed around this time. The atmosphere is composed of volcanic and greenhouse gases. 

• Proterozoic(2,500-541 MYA) : Eukaryotes, a more complex form of life, emerge, including some forms of multicellular organisms. Bacteria began producing oxygen, shaping the third and current of Earth's atmospheres. Plants, lately animals and possibly earlier forms of fungi form around this time. The early and late phases of this eon may have undergone "Snowball Earth" periods, in which all of the planet suffered below-zero temperatures. The early continents of Rodinia and Pannotia, may have formed around this time, in that order.

• Phanerozoic(541 - present) : Complex life, including vertebrates, began to dominate the Earth's ocean in a procedures known as the Cambrian explosion. Gradually, life expanded to land and all familiar forms of plants, animals and fungi began appearing, including annelids, insects and reptiles. Several mass extinctions occur, among which birds, the descendants of dinosaurs, and more recently mammals emerge. The rise and evolution of the human species occur at the very recent phases of this eon.

The Last eon, the Phanerozoic, is represented by its three component eras: the Palaeozoic; the Mesozoic, which spanned the rise, reign, and climactic extinction of the huge dinosaurs; and the Cenozoic, which presented the subsequent development of dominant mammals on Earth. 

The Paleozoic ("old life") era was the first and longest era of the Phanerozoic eon, lasting from 542 to 251 MYA. During the Paleozoic, many modern groups of life came into existence. Life colonized the land, first plants, then animals. Two major extinctions occurred. The continents formed at the break-up of Pannotia and Rodinia at the end of the Proterozoic slowly moved together again, forming the supercontinent Pangaea in the late Paleozoic.

The Mesozoic ("middle life") era lasted from 251 Ma to 66 Ma. It is subdivided into the Triassic, Jurassic, and Cretaceous periods. The era began with the Permian–Triassic extinction event, the most severe extinction event in the fossil record; 95% of the species on Earth died out. It ended with the Cretaceous–Paleogene extinction event that wiped out the dinosaurs.

Dinosaurs were the dominant terrestrial vertebrates throughout most of the Mesozoic

The Cenozoic ("new life") era began at 66 MYA, and is subdivided into the Paleogene, Neogene, and Quaternary periods. Mammals, birds, amphibians, crocodilians, turtles and lepidosaurs were able to survive the Cretaceous–Paleogene extinction event that killed off the non-avian dinosaurs and many other forms of life, and this is the era during which they diversified into their modern forms.

Human History In Brief completes One Year