Journey to the center of the earth

 
Journey to the center of the earth

 Ever wondered what our earth is made of?  Think of it as an apple.  An apple constitutes the skin, the pulp and the core in the middle.  Similarly, the earth is made up of the thin outermost layer called the crust, the 

innermost part called the core, and the part in between them called the mantle.

         The outer most layer is crust which classified in to two parts 

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which forms the continents the areas of shallow seabed close to their shores, known as continental shelves

Consisting mostly of granitic rock, continental crust has a density of about 2.7 g/cm3 and is less dense than the material of the Earth's mantle (density of about 3.3 g/cm3), which consists of mafic rock. Continental crust is also less dense than oceanic crust (density of about 2.9 g/cm3), though it is considerably thicker; mostly 25 to 70 km versus the average oceanic thickness of around 7–10 km. About 40% of the Earth's surface is now overlaid by continental crust. Continental crust makes up about 70% of the volume of Earth's crust.

A contour map of the thickness of the Earth's crust (numbers in kilometres)

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick, however it is denser, having a mean density of about 2.9 grams per cubic centimeter as opposed to Continental which has a density of about 2.7 grams per cubic centimeter.

 Oceanic crust :is significantly simpler than continental crust and generally can be divided in three layers.

Layer 1: is on an average 0.4 km thick. It consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Near the continental margins sediment is terrigenous, meaning derived from the land, unlike deep sea sediments which are made of tiny shells of marine organisms, usually calcareous and siliceous, or it can be made of volcanic ash and terrigenous sediments transported by turbidity currents.

Layer 2: could be divided into two parts: layer 2A – 0.5 km thick uppermost volcanic layer of glassy to finely crystalline basalt usually in the form of pillow basalt, and layer 2B – 1.5 km thick layer composed of diabase dikes.

Layer 3 : is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and cumulate ultramafic rocks. It constitutes over two-thirds of oceanic crust volume with almost 5 km thickness

Age of oceanic crust. The red is most recent, and blue is the oldest.

The mantle

is the layer located directly under the sima. It is the largest layer of the Earth, 1800 miles thick. The mantle is composed of very hot, dense rock. This layer of rock even flows like asphalt under a heavy weight. This flow is due to great temperature differences from the bottom to the top of the mantle. The movement of the mantle is the reason that the plates of the Earth move


Two main zones are distinguished in the upper mantle: the inner asthenosphere composed of plastic flowing rock about 200 km thick, and the lowermost part of the lithosphere composed of rigid rock about 50 to 120 km thick.A thin crust, the upper part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick.

In the mantle, temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper       boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core.
 Although the higher temperatures far exceed the melting points of the mantle rocks at the surface (about 1200 °C for representative peridotite), the mantle is almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents melting, because the temperature at which melting begins (the solidus) increases with pressure

Earth's mantle

The core
Lying more than 5,000km beneath our feet, at the centre of the Earth, the core is beyond 
the reach of direct investigation. it consists of a solid sphere of metal sitting within a liquid outer core.

The outer: core of the Earth is a liquid layer about 2,266 km (1,408 mi) thick composed of iron and nickel which lies above the Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath the Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km (3,200 mi) beneath the Earth's surface.The temperature of the outer core reach to 4400 °C,8000 °F

The inner core: of the Earth, its innermost part, is a primarily solid ball with a radius of about 1,220 km (760 mi), according to seismological studies. (This is about 70% of the length of the Moon's radius.) It is believed to consist primarily of an iron–nickel alloy, and to be about the same temperature as the surface of the Sun: approximately 5700 K (5430 °C.

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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. 

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