Lect 2.1 Origin Earth UPES Feb 4 2k15
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Transcript of Lect 2.1 Origin Earth UPES Feb 4 2k15
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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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