Origin of the Earth
Origin of the Earth
Centrifugal force (acts outwardly away from the centre of rotation)
Equator & Pole
Angular momentum is the measure of the
tendency of a rotating body to remain rotating.
Origin of the Earth
The origin of our planet can be broadly grouped into two: Uniformitarian or
Uni-parental hypothesis and Cataclysmic or Bi-parental hypothesis
Origin of the Earth
1. Uniformitarian or Uni-parental Hypothesis
1.1 Nebular Hypothesis [1775 & 1796]
1.2 Meteorite Hypothesis (Inter-Stellar Dust Hypothesis) [1943]
2. Cataclysmic or Bi-parental Hypothesis
2.1 Planetesimal Hypothesis [1905]
2.2 Gaseous Tidal Hypothesis [1916]
Nebular Hypothesis
The German philosopher Kant (in 1755) and the French mathematician
Laplace (in 1796) independently developed the Nebular hypothesis based
on the hot origin of our planets.
The hypothesis suggests that a single incandescent gaseous nebula formed
the Solar System
Gradually, as it
cooled, it contracted
in size, resulting in an
increase in its rate of
rotation and
centrifugal force.
Nebular Hypothesis (Evaluation)
The Sun, which is the remnant of the ancient nebula, would have been
rotating now at a great speed and would probably have been ready to give
rise to another ring, to form another planet. [Sun’s angular momentum]
No mechanism is proposed to explain how the hot gaseous material
condensed into rings.
Meteorite hypothesis (Interstellar Dust
Hypothesis)
This hypothesis was put forth by a Soviet scientist Otto Schmidt in 1943.
According to the Inter-Stellar Dust Hypothesis, our sun during its galactic
revolution captured the dark matter of the Universe.
Meteorite hypothesis (Interstellar Dust
Hypothesis)
• The dark matter after being attracted by
the sun during its galactic revolution
started revolving around the primitive
rotating sun : Interstellar dust
• Gases: destabilised & less systematically
arranged and Dust: stabilised and
systematically arranged.
• The dust particles after being combined
and condensed were changed into a at
disc which started revolving around the
Sun.
• With the passage of time, these embryos
captured more and more matter and thus
grew in size to become asteroids.
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Interstellar Dust Hypothesis (Evaluation)
The drawbacks of the hypothesis were -
(a) improbability of the Sun capturing a cold cloud of gas and
dust (meteorites) and
(b) dif culty in explaining the concentric inner surface of the
earth.
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Planetesimal Hypothesis
American scientists, Thomas Chamberlin and Forest Moulton, in 1905
suggested that the planets were formed from the collusions and union of
numerous small planetary fragments called Planetesimals.
The hypothesis assumes that Sun existed even before the formation of
planets
Planetesimal Hypothesis
There are two major objections to this theory:
(a) such large angular momentum cannot be produced by the
passing star and
(b) the theory completely fails to explain how the Planetesimals
coalesced into a planet.
Gaseous Tidal Theory
The Gaseous Tidal Hypothesis was postulated by James Jeans,
a British astronomer in 1916.
According to him, the Solar System was formed from the Sun
and another intruding star.
Sun/ Proto Sun - ‘intruding star’ in the Universe - Filament
Sun
Intruding Star
Filament: bulging in
the centre and
tapering at both ends
