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Origin Of EarthFebruary-2015

n.k.agarwal

ex-Director, GSI

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Earth is part of Solar System and the Solar

System is part of The Milky Way Galaxy, which

is one of the Galaxies in the Universe.

Scientists have been studying the creation of

universe for last many centuries.

It is now thought that the Universe was

created through a Big Bang some 15 billion

years ago.

Earth, Planets, Sun has a common heritage or origin

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The universe holds everything from the tiniest

particle to the clusters of galaxies (consisting

of stars, planets etc. in a medium of gas and

dust all held together by gravity.

Our galaxy, the Milky Way, part of the universe

has hundreds of billions of stars, gas and

dust held together by gravity).

Earth, Planets, Sun has a common heritage or origin

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ENERGY and MASS TRANSFORMATION

The Big Bang~15 billion years ago

B

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Ma= Million Anum = 10x6 Ga= Giga Anum = 10x9

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The Big Bang theory states that the

universe was formed about 15 billion years

ago from a giant explosion when suddenly

energy transformed into matter. At present

there is no answer from where this energy

came .

This matter expanded and started to cool

down, going through different transitional

phases.

The universe has been expanding ever since.

The Big Bang

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V

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Solar Nebula Rotating cloud of dust and gases (Hydrogen and Helium) begins to contract (~5bya).

Material assumes a flat, disk shape.

Most of the material gravitationally swept to the center forming the protosun (Pre-Sun).

Planets begin to accrete from the material in the flattened disk which is orbiting the sun, due to gravitational effects.

In time, most of the material is swept into planets/moons or lost into space.

Big Bang to Formation of

Solar System

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Planetary segregation due to pressure, gravitational, and temperature gradients (chemical differentiation).

The most refractory particlessurvived the hottest part of the contracting nebula.

Inner rocky planets are:

High density

Small in size

Composed of metallic and rocky substances (Fe, Ni, Si, Ca, Na)

Big Bang to Formation of

Solar System

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The gases were vaporized or swept away by the solar wind.

These materials could only exist in the cooler outer regions of the nebula.

Outer gaseous planets are:

Low density

Large in size

Formed primarily from ices (H2O, CO2, CH4, and NH3-Ammonia) and gases (H2 and He)

Big Bang to Formation of

Solar System

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According to the Big Bang theory, the solar

system was formed from a cloud containing

dust and gas i.e. Hydrogen, helium etc. known

as Nebula.

As the nebula contracted, it spun rapidly,

leading to frequent collisions between dust

grains.

This nebula grew hotter and denser, forming a

disk of gas and dust at its centre.

Eventually the hot centre of the nebula formed

a star - the sun.

Making of Solar System

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The particles of nebula dust started sticking

together, eventually forming planets and their

satellites.

Different planetary particles left over from this

initial explosion can still be found flying

around in space. These particles are called

meteorites.

By studying these meteorites, scientists have

found that our solar system is about 4600 m.y.

old.

Making of Solar System

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The Origin of the Earth

~15 billion years ago :The Earth and the other 8 planets and the

Sun accreted at about the same time from a

vast cloud of dust and gas (nebula).

~5 billion years ago :The nebula began to gravitationally contract,

began to rotate and flattened. Eventually, the

Sun ignited (fusion) and the newly formed

planets began to differentiate - heavier

elements and chemical components sank to

the center and rocky material formed the

crust. The newly formed planets and moons

released gas forming early atmospheres.

Making of Solar System

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Making of Solar System

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Solar System

Inner Planets Outer PlanetsAsteroids 14

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Earth From Outer Space

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http://ep.yimg.com/ca/I/spaceimages_2114_11521197

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Origin of Planet Earth

Most researchers

believe that Earth and

the other planets formed

at essentially the same

time from the same

primordial material as

the Sun.

Early Evolution of Earth

Layered structure developed by chemical

segregation early in the formation of the Solar

System and the Earth.

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The earth on which we are live is a Unique

planet of the solar system.

1. Polar diam. : ~ 12,714 km

2. Equatorial diam. : ~ 12,756 km

3. Circumference : 40, 000km

4. Surface Area : ~ 510 m.sq.km.

5. Volume : 1042 billion cu.km

6. Mass : 5.97 10 21 tonnes

7. Dist. From the sun : 150 million km

8. Average surface temperature : 14C

The basic statistics of the earth

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The cosmologists have developed 2 basic

hypothesis for the origin of the earth or strictly

speaking the origin of the Solar system

1. Single body hypothesis - the planets were

formed without intervention from forces

outside the solar system (No object other

than the Sun was involved)- Single Star

Hypothesis.

Hypothesis for the Origin of Earth

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2. Second body hypothesis - Assumes that the

solar system originated as a result of forces

created by the accidental interference of

another celestial object. It presumes that

another star passed close to the sun (2 star

hypothesis)

Hypothesis for the Origin of Earth

From these basic two

Hypotheses a number of Hypotheses have

been generated.

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Perhaps the oldest scientific explanation.

By Kant in 1775 & Laplace in 1796.

This hypothesis assumes the existence of a

large globular mass of gas called nebula,

slowly rotating through the space.

This nebula gradually became smaller due to

its inherent gravitational pull.

(1) The Nebular Hypothesis(Single Star Hypothesis)

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During the rotation, the nebular mass started

cooling and contracting simultaneously.

As it contracted, its speed of rotation

increased.

Eventually the outermost part of the nebula

rotated so rapidly that rings of gas got

separated from the shrinking nebular body.

These rings slowly got condensed to form the

planets and the central mass became the sun.

(1) The Nebular HypothesisSingle Star Hypothesis (contd.)

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Origin of Solar System from Nebula

(Single Star Hypothesis)

Globular Nebula

Separation of

Gaseous Rings

Separation of

Gaseous Rings

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1. If this hypothesis worked and the origin of the

solar system actually did take place, the sun

should have been having the greatest angular

momentum, because it is the most massive

part of the solar system and it (sun) lies at the

centre of the system. But actually, the sun is

having only 2% of the total angular momentum.

2. Such detached rings of gas should have been

dissipated in space rather than getting

condensed into solid particles.

Drawbacks of Nebula Hypothesis

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1. Proposed by Chamberlin & Moulton in 1904.

2. Assumes the existence of two stars in space

in the very beginning.

3. The sun was considered to be one of these

two stars existing before the formation of the

planets.

4. When the intruder star passed by the sun,

it exerted a gravitational force on the sun &

pulled masses of solar material.

(2) The Planetesimal Hypothesis2- Star Hypothesis

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5. This detached material was dragged along in

the direction of movement of the passing star,

and later got cooled & condensed into solid

particles called planetesimals. each moving

in its own orbit around the sun.

6. These planetesimals acted as nuclei that

attracted other planetesimals, and by

accretion, the planets eventually grew to their

present sizes.

7. Other smaller clusters of planetesimals, formed

the satellites.

8. As per this hypothesis, the angular momentum

of the planets was derived from the pull of the

passing star.

(2) The Planetesimal Hypothesis2- Star Hypothesis (contd.)

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1. The motion of the planetesimals could not

possibly be produced by the passing star .

2. It is highly unlikely that another star could

have passed so close to the sun and the

intruder star could have generated sufficient

thrust to set the detached solar masses in

motion in orbits. Instead, it is more likely that

such masses would simply diffuse into the

space.

Drawbacks of The Planetesimal Hypothesis

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Important Alternative to The Planetesimal

Hypothesis

(2)(i) The Tidal Hypothesis

(2- Star Hypothesis)

(3) The Turbulent Hypothesis

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Hypothesis given by Jeans & Jeffrey, two

British Astronomer.

Assumed that tides were created on the sun,

due to the force of attraction between the sun

and a passing star.

(2)(i) The Tidal Hypothesis

2-Star Hypothesis

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Due to this tidal action, a gaseous filament

got separated from the sun, as soon as the

passing star went away.

This separated filament was in the form of a

spindle & was unstable.

It further broken down into a number of small

fragments, each of which condensed to form

planets.

Some of these planets further broken down

into pieces and formed satellites.

(2)(i) The Tidal Hypothesis

2-Star Hypothesis

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(2)(i) The Tidal Hypothesis

2-Star Hypothesis

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1. The passing star cannot possibly

impart the proper angular momentum to

the gaseous filament

2. A hot filament pulled from the sun would

not form solid planets but simply diffuse

into the space.

Drawbacks of The Tidal Hypothesis2-Star Hypothesis

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1. Latest & widely accepted.

2. First proposed by a German physicist in

1944.

3. In the same year, his views were supported

(with some modification) by Schmit, a Soviet

mathematician.

4. In 1951, Kuiper, an American scientist

modified this hypothesis and proposed the

same.

(3) The Turbulent Hypothesis or The

Protoplanet Hypothesis

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5. The hypothesis says that in the very

beginning, there was a hot gaseous nebular

mass, rapidly rotating in space.

6. This nebula, due to gravitational attraction,

formed a disc of cloud & dust.

7. Because of its rotating nature, this nebular

disc developed large whirlpool (eddies) at

various places.

(3) The Turbulent Hypothesis or The

Protoplanet Hypothesis

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8. Ultimately these eddies got separated from

the nebular masses.

9. These independent eddies also contained a

whole system of smaller eddies.

10. These eddies might then have collected the

surrounding dusty material by gravitational

attraction, thus forming swirls of dust and

gas, called protoplanets.

(3) The Turbulent Hypothesis or The

Protoplanet Hypothesis

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11. It is believed that such protoplanets

represent the present day planets.

12. These original protoplanets were much

larger than the finished planets.

13. Smaller eddies got developed inside some

of the larger eddies, giving rise to spinning

discs that became the satellites or moons of

the planets.

(3) The Turbulent Hypothesis or The

Protoplanet Hypothesis

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Many of the astronomers today support

this hypothesis of the Protoplanet

hypothesis.

The observations (through telescopes)

have revealed numerous nebulas

between the stars.

It is significant that some of these

massive eddies of gas & dust are

actually condensing to form new stars.

Present Understanding

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The origin of the earth still remains a

subject of Study

Still a BIG QUESTION - ?

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This chapter helps you in understanding :

1. What is the relation between Earth, Solar System

and Universe?

2. How Solar System was formed?

3. How earth was formed and what is the current

hypothesis about the origin of Earth?

Summary :

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