story of the earth

 story of the earth

    from long time we live on the earth without thinking how and when it started?let me take you in a short trip through time to see and know how and when our earth was formed.

    Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar  System. Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600 to 540 million years ago, then finally Pangaea, which broke apart 180 million years ago.

   Geologists have organized the history of the Earth into a timescale on which large chunks of time are called periods and smaller ones called epochs. Each period is separated by a major geological or palaeontological event, such as the mass extinction of the dinosaurs which occurred at the boundary between the Cretaceous period and the Paleocene epoch.
Archean era
 3.8 billion–2.5 billion years ago. It was during the Archean era thants, just small islands in a shallow ocean.

Cryogenian period
 850 million–635 million years ago. A succession of incredibly harsh ice ages waxed and waned during the Cryogenian. It is nicknamed Snowball Earth as it's been suggested that the 
glaciation was so severe it may even have reached the equator.

 Ediacaran period
 635 million–545 million years ago .Known also as the Vendian, the Ediacaran was the final stage of Pre-Cambrian time. All life in the Ediacaran was soft-bodied - there were no bones,shells, teeth or other hard parts

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Cambrian period
 545 million–495 million years ago. The Cambrian is famed for its explosion of abundant and diverse life forms. Life had diversified into many forms and many ways of living: animals now 
swam, crawled, burrowed, hunted, defended themselves and hid away

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Ordovician period
 495 million–443 million years ago.During the Ordovician, a few animals and plants began to explore the margins of the land, but nothing colonised beyond these beachheads, so the majority of life was still confined to the seas.

  
Silurian period
443 million–417 million years ago .The Silurian period was the time when reefs got their act together, grew really big and created a completely new type of ecosystem for marine life.

Devonian period
 417 million–354 million years ago.The Devonian is also known as the Age of Fishes, since several major fish lineages evolved at this time. Sea levels were high and the global climate was warm. 

Carboniferous period
 354 million–290 million years ago.The Carboniferous is famed for having the highest atmospheric oxygen levels the Earth has ever experienced and for the evolution of the first reptiles. Plants grew and died at such a great rate that they eventually became coal. The period was originally called the Coal Measures after its proliferation of coal-bearing rocks.

 
Permian period
 290 million–248 million years ago.The Permian started with an ice age and ended with the most devastating mass extinction the Earth has ever experienced. In fact, at least two mass extinctions occurred during this time. It's also when all the continents of the world finally coalesced into one supercontinent, named Pangaea (meaning 'the entire Earth') .

Triassic period
 248 million–205 million years ago.The Triassic began after the worst mass extinction ever, at the end of the Permian. Life on Earth took a while to recover and diversify. The Triassic was characterised by heat, vast deserts and warm seas. 

Jurassic period
 205 million–142 million years ago.The Jurassic began after the mass extinction event that ended the Triassic. Life, however, was quick to recover from this blow and the Jurassic eventually became host to the most diverse range of organisms that Earth had yet seen. 

Cretaceous period
 142 million–65 million years ago.The Cretaceous ended with the most famous mass extinction in history - the one that killed the dinosaurs. Prior to that, it was a warm period with no ice caps at the poles. 

Palaeocene epoch
65 million–54.8 million years ago .The Paleocene epoch was a time of dense forests and evolutionary experiments. The extinction of the dinosaurs and other giant reptiles at the end of the Cretaceous paved the way for mammals and birds to evolve to fill those empty niches, so many new creatures appeared

Eocene epoch
54.8 million–33.7 million years ago .The Eocene began as a time of global warming, with temperatures across the planet soaring. Forests thrived and trees grew even in polar regions. Eventually, the Eocene became cooler and drier. 

Oligocene epoch
 33.7 million–23.8 million years ago.Over 30 million years ago, the Oligocene epoch saw the start of the global cooling that would eventually shift the Earth's climate to one where glaciers were present and ice ages were possible. Worldwide, this was the time when grasslands began to expand and forests - especially tropical ones - shrank correspondingly. Animals evolved to fit the new, open landscape and many fast-running prey and predator species arose as a result. 

Miocene epoch
23.8 million–5.3 million years ago .The apes arose and diversified during the Miocene epoch, becoming widespread in the Old World. In fact, 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.

Pliocene epoch
 5.3 million–2.6 million years ago.The Pliocene world looked very similar to Earth today as North and South America had been drifting ever closer and the gap between them was sealed in this epoch.

 
Pleistocene epoch
 2.6 million–11.7 thousand years ago.During the Pleistocene, glaciers came and went, resulting in a series of ice ages punctuated by warmer periods. There were at least 20 cycles of this advance and retreat. During the ice ages, global temperatures were 5 degrees centigrade cooler than today and it was much drier, since much of the world's water was locked up in massive ice sheets.

 
Holocene epoch
 11.7 thousand years ago–present day.The Holocene (or Recent) is the current geological epoch which started some 11,500 years ago when the glaciers began to retreat. This retreat marked the end of the glacial phase of the most recent ice age. Its character was set by the spread of forests as the ice retreated and then by their shrinkage as mankind's demand for timber and agricultural land grew. Although we think of the Holocene as a warm time for the planet, we are still in an ice age. This is indicated by the presence of ice caps at the poles - the planet as a whole is just in an interglacial phase.

     Now we  complete our life routine after  backing from this interesting trip through the earth's history.