Origin of Earth.docx

8/10/2019 Origin of Earth.docx

1/12

Origin of Earth

The origin of universe is considered to have taken place about 14.4 billion years ago

In the beginning, the universe was all in one place. All of its matter and energy were squished into

a singularity and then it eploded.The tremendous amount of material blown out by the eplosion

eventually formed the stars and galaies. After about 1! billion years, our solar system began to

form.

"ne of the hypothesis about the origin of our solar system is the Nebular hypothesis.

The Nebular Hypothesis

A large gas cloud #nebula$ begins to condense. %ost of the mass is in the center, there is

turbulence in the outer parts. &mall chunks #mass$ grow and collide, eventually becoming large

aggregates of gas and solid chunks.

'ravitational attraction causes the mass of gas and dust to slowly contract and it begins to rotate

The dust and matter slowly falls towards the center forming stars.

Origin Of Earth Rakesh Page 1


2/12

About five billion years ago, some of this gas and matter became our sun.

At first, it was a hot, spinning cloud of gas that also included heavier elements.

As the cloud spun, it collected into a disc called a solar nebula. "ur planet and others probably

formed inside this disc. The center of the cloud continued to condense, eventually igniting and

becoming a sun.

about 4.( billion years ago, the )arth formed as particles collected within a giant disc of gas

orbiting this sun. The oldest rocks geologists have been able to find are *.+ billion years old based

on radiometric dating.

Components of Earth

ithosphere

Atmosphere

-ydrosphere

iosphere

Lithosphere

"utermost part of a rocky planet.

In case of earth, lithosphere comprises of crust and upper part of mantle.

It is hard and rigid layer of the earth

The lithosphere provides a conductive lid atop the convecting mantle/ as such, it affects

heat transport through the )arth.

The lithosphere is broken into tectonic plates.

There are two types of lithosphere0

o "ceanic lithosphere, which is associated with "ceanic crust and eists in the ocean

basinso ontinental lithosphere, which is associated with ontinental crust



3/12

o "ceanic lithosphere is typically about 2!31!! km thick #but beneath the midocean

ridges is no thicker than the crust$

ontinental lithosphere has a range in thickness from about 4! km to perhaps 5!! km/ the

upper 6*! to 62! km of typical continental lithosphere is crust.

Atmosphere

An atmosphere #'reekatmos7vapor and sphaira7sphere$ is a layer of gases that surround

the earth and is held in place by the gravity of the earth.

The atmosphere protects life on )arth by absorbing ultraviolet solar radiation, warming the

surface through heat retention, and reducing temperature etremes between day and night

#the diurnal temperature variations$.

The atmospheric composition on )arth is largely governed by the byproducts of the very

life that it sustains.

)arth8s atmosphere contains roughly #by molar content9volume$ :;.!;< nitrogen, 5!.+2ight after its creation, the )arth is thought to have had a thin atmosphere composed

primarily of helium #-e$ and hydrogen #-$ gases

The )arth?s gravity could not hold these light gases and they easily escaped into outer

space

Today, - and -e are very rare in our atmosphere



4/12

Hydrosphere

ombined mass of water found on, under and above the surface of the earth.

The total mass of the )arth8s hydrosphere is about 1.4 @ 1!1; tons, which is about !.!5*emember, that comets are best described as Cdirty ice ballsD

The earliest evidence of surface water on )arth dates back about *.; billion years

The portion of earth?s surface where water is in solid form including seaice, glacier, snow,

icecaps, ice sheets and froen ground is called cryosphere. This has a wide overlap with

the hydrosphere.

Biosphere

The biosphere is the global sum of all ecosystems. It can also be called the one of life on

)arth, a closed and selfregulating system

This includes part of atmosphere, lithosphere and hydrosphere

Erom an ecological point of view, the biosphere is the =global ecosystem=, comprising the

totality of biodiversity on earth and performing all manner of biological functions, including

photosynthesis, respiration, decomposition, nitrogen fiation and denitrification.



5/12

Structure of EarthThe structure of earth is divided based on two methods %echanically0

ithosphere hard and rigid outermost layer of earth

Asthenosphere highly viscous, mechanically weak and ductilelydeforming layer

%esosphere more denser and rigid layer below asthenosphere

"uter core highly dense liquid core

Inner core highly dense solid core hemically

o rust thin, rigid layer rich in silica and alumina

o %antle composed of silicate rocks that are rich in iron and magnesium relative to the

overlying crusto ore rich in heavy elements like iron and transition elements.

"uter and

Inner



6/12

eological Time Scale

The geologic time scale provides a system of chronologic #time$ measurement relating

stratigraphy to time that is used by geologists, paleontologists and other earth scientists to

describe the timing and relationships between events that have occurred during the history

of the )arth.

The geological time scale is divided into )on, )ra, Feriod and )pochs.



7/12

!recambrian

The Frecambrian #Freambrian$ is the name which describes the large span of time in

)arth8s history before the current Fhanerooic )on

Frecambrian includes approimately +!< of geologic time. It etends from 4.( billion years

ago to the beginning of the ambrian Feriod #about 2:! %a$

&olidification of first earth crust. 4!!! ma

Eirst rain/ formation of epanses of water/ erosion and sediments accumulation. *;!! ma

Eirst sedimentary rocks. *:2! ma

Eirst structure of possible biogenic origin #Gnicellular algae or acteria$. *5!! ma

Eirst stromatolites #fossil made from cyanobacteria$. 5+!! ma

Eirst certain fossil Algae. 55!! ma

Eirst soft bodied animals. 12!! ma

Eirst association of multicellular soft bodied animals. :!! ma

'reat glaciations. (2! ma

!alaeo"oic

ambrian0 Eirst animal with shells and skeletons. 2:! ma "rdovician0 Eirst vertebrates, Eish appear. 2!! ma

&ilurian0 ife emerges from the water, invading the continents. 44! ma

Hevonian0 ollision between )urope and orth America, *+2 ma

arboniferous0 'reat forests and diffusion of winged insects. *42 ma

Fermian0 ollision between Asia and )urope/ Grals #mountain chain in >ussia$ born/ all the

continents merge into one Fangaea/ Appalachians mountain of G&A born. 5;! ma

At the end of Fermian was the greatest )tinction of all time

52! million years ago, in the Fermian Bust within a few thousand years, +2< of the life

forms on the planet were wiped out, in the biggest mass etinction )arth has ever

known. 'eological data to eplain the destruction have been hard to find, simply because the

rocks are so old and therefore subBect to all kinds of erosion processes. The etinction

may be due to some catastrophic environmental change across vast swathes of the

planet.

hief suspects include sealevel fluctuations, volcanic activity, space impacts and

melting methaneice in sea sediments#eso"oic

Triassic0 >eptile kingdom established. 552 ma Jurassic0 Fangea starts to splits up/ the Atlantic starts to open. Eirst fish appear. 1+! ma

retaceous0 ulmination of reign of Hinosaurs which then die out. At the same time the

Ammonites #etinct invertebrate ocean animal with a flat partitioned spiral shell$ and

microscopic 'lobotruncata disappear in the oceans. 1*( ma

The supercontinent of Fangaea, mostly assembled by the Triassic, allowed land animals to

migrate from the &outh Fole to the orth Fole. ife began to rediversify after the great

FermoTriassic etinction and warmwater faunas spread across Tethys.

Huring the retaceous the &outh Atlantic "cean opened. India separated from

%adagascar and raced northward on a collision course with )urasia. otice that orth

America was connected to )urope, and that Australia was still Boined to Antarctica.

The impact of a 1! mile wide comet caused global climate changes that killed the dinosaurs

and many other forms of life. y the ate retaceous the oceans had widened, and India

approached the southern margin of Asia.



8/12

Ceno"oic

Faleocene0 )mergence of rocky mountains/ mammal kingdom born. (2 ma

)ocene0 ollision between India and )urasia/ 'rowth of -imalayas. 2*24 ma

"ligocene0 ollision between Africa and )urasia/ Alps and Appennines start to develop.

*:*; ma

eogene%iocene0 )mergence of Andes. 5( ma

Kuaternary

Fleistocene0 %aBor Kuaternary glaciations. Appearance of %an. 1.; ma

-olocene0 )nd of glaciations. >ise in sea level. %an farming. !.!1 ma

$i%e E&tinctions Almost 44! million years ago, some ;2 percent of marine animal species were wiped out in

the earth8s first known mass etinction.

>oughly *(: million years ago, once again many species of fish and :! percent of marine

invertebrates perished in a maBor etinction event.

Then about 542 million years ago, up to +2 percent of all animals nearly the entire animal

kingdoms were lost in what is thought to be the worst etinction in history.

&ome 5!; million years ago, another mass etinction took a toll primarily on sea creatures,

but also some land animals.

(2 million years ago, three quarters of all species including the dinosaurs were eliminated.

!hysical $eatures of Earth Surface

)arth8s outermost layer is fragmented into a doen or more large and small plates

that are moving relative to one another as they ride atop hotter, more mobile

material.

The breaking and bending of earth?s crust under internal forces of earth is termed

tectonic movements. These forces cause rocks to bend, fold, change, break.

They cause the landforms to change, mountains and basins to form

These all occur due to the forces or the differential stresses acting upon the rocks.

Le will look into some of the landforms generally produced due to the tectonic

movements in continents and oceans.

#ountains

A feature that towers or rises above the level of surrounding area more or less abruptly

Gsually mountains occur in chains or ranges

-ave comple structures due to folding, faulting, volcanic activity, igneous intrusions etc.

Hifferent types of mountains have different methods of origin

Types of mountains

Eold mountains

lock mountains

Molcanic mountains and

>esidual mountain

$old mountain



9/12

It results from the earth?s crust being compressed from

the sides

The layers of rocks in the crust are pushed up to form a

fold mountain.

Alps, -imalayas, Andes are the eamples.

Bloc' mountains

%ountains formed due to faulting.

A part of the land block is depressed so that the remaining block stands conspicuously

above the surroundings.

The uplifted section is termed the block mountain #horst$ Lhen the middle section falls down instead of going up, it forms the rift valley #graben$.

(olcanic mountains The outrushing magma forms the fissures the crust of the earth at a place into a dome,

mountains formed in such a way are called volcanic or lacolith mountains. Molcanoes emit gases, liquid, solids as well.

The gases are lost in atmosphere but the liquid and solid get accumulated and heaps

around the fissure or orifice. Huring continued activity for years, the accumulation grow into an enormous sie Bustifying

the name mountain.



10/12

)esidual mountain

Lhen eisting mountains or plateaus

are in eroding state the resulting

structures are called residual

mountains or relict mountainsThe eroding agents are snow, wind,

rainThey erode the softer materials from

the eisting mountains thus reshaping

the lower hills and valleys



11/12

!lateaus

Flateau or Ntablelands? are relatively flat area more than 5!! m high.

It?s one side may rise steeply from the flat area while other side may drop steeply from the

flat area. In some plateaus all the sides may drop away.

Types of plateaus

Fiedmont plateau0 lying at the base of a mountain

Intermont0 plateau surrounded by mountain ranges ontinental0 flat, large island plateau. e.g. 'reenland

Shields

arge region of eposed basement rock 9Frecambrian igneous rock #older than 2:! million

years old and sometimes dates back 5 to *.2 billion years$ with gentle conve surface

surrounded by sediments.

"rigin is mostly volcanic but highgrade metamorphic rocks also found

Tectonically stable

Are relatively flat regions where mountain building, faulting, and other tectonic processesare greatly diminished compared with the activity that occurs at the margins of the shields

and the boundaries between tectonic plates.

*nternal Structure Of Earth

Crust

O Gppermost solid shell of the earth.

O >igid and very thin compared with other two layers

O The thickness of crust varies in oceans and continents

3 under the oceans0 2( km

3 under the continents0 *!*2 km

3 under the mountains0 (!:! km

3 Average thickness of the crust0 *2 km

O &ilica #&i"5$ and alumina #Al5"*$ are the most dominant component of the crust.

O &olid aggregate that make up the crust is termed Nrock?.

O &cientists believe that below the lithosphere is a relatively narrow #52!*2! km$, mobile

one in the mantle called the asthenosphere (from asthenes, Greek for weak).

O This one is composed of hot, semisolid material, which can soften and flow after being

subBected to high temperature and pressure over geologic time. The rigid lithosphere is

thought to =float= or move about on the slowly flowing asthenosphere.

#antle

O The seismic velocity abruptly increases further inside the earth marking the mantle.

O It is separated from the crust by N%ohorovicic discontinuity? or N%oho?.

O %antle is also divided as upper, middle and lower mantle.

O The upper and middle mantle is about 1!!! km thick.

O "rigin of magma, triggering of earthquake, tectonics takes place in this upper and transition

one mantle.

O The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter

and denser because temperature and pressure inside the )arth increase with depth.O ut very little is known about the mantle as all the observation have been of indirect nature

#mostly by the behaviour of the seismic waves$

O The lower mantle is more homogenous and reaches up to 5+!! km depth.



12/12

Core

O &eparated by N%antlecore Hiscontinuity? from the mantle the core reaches the centre of

earth.

O onstitutes 1: < of the volume and *4< of mass of earth.

O &wave do not pass through the core indicating the core is liquid. The velocity of the F

wave also decreases from 15.( to ;.4 km9sec.

O The core is made up of iron and transition elements.

O )arth8s core is actually made up of two distinct parts0 a 5,5!! kmthick liquid outer core and

a 1,250 km-thick solid inner core.

O As the )arth rotates, the liquid outer core spins, creating the )arth8s magnetic field.

O The density of the core varies from 2.2 1!*kg9m*to 1!.( 1!*kg9m*. the density at core

is up to 1* 1!*kg9m*

O The temperate is etremely high #(!!!P$ and so is the pressure #* million atmospheres$

Shado+ "one

O &cientists deduced the structure of )arth8s interior and how waves move through it by

analying thousands of earthquakes recorded at )arth8s surface.O &ome of the areas on the surface do not receive any waves Q these areas are called the

shadow one

O 4*2! km belt around the earth

O Fwaves are refracted below the boundary between the earth?s core and mantle.

O &waves cannot reach there as they don?t pass through the molten core.

O This non penetration of &waves here was a evidence of the outer core being in liquid state.

Origin of Earth.docx

Documents

Transcript of Origin of Earth.docx