Explore the origin and evolution of Earth, from the Big Bang to the formation of our planet. Learn about key geological processes, historical milestones, and the scientific theories explaining Earth's formation and development.
Various hypotheses proposed by philosophers and scientists.
Nebular Hypothesis:
Proposed by Immanuel Kant and revised by Laplace in 1796.
Planets formed from a cloud of material around a youthful sun.
Star Interaction Hypothesis:
Proposed by Chamberlain and Moulton in 1900.
A wandering star caused material separation from the sun.
Material condensed into planets.
Binary Theories: Involving a companion to the sun.
Revised Nebular Hypothesis:
Proposed by Otto Schmidt and Carl Weizascar.
Planets formed via accretion from a solar nebula of hydrogen, helium, and dust.
Modern Theories
Origin of the Universe
Big Bang Theory (Expanding Universe Hypothesis):
Proposed by Edwin Hubble in 1920.
Key points:
All matter existed in a “tiny ball” with infinite density and temperature.
The Big Bang occurred 13.7 billion years ago.
Rapid expansion within fractions of a second.
Within 3 minutes, first atoms formed.
Within 300,000 years, temperature dropped to 4,500K, giving rise to atomic matter.
Universe expansion involves increasing space between galaxies.
The singularity concept in the Big Bang theory, exploring the origin of the universe from a singular point in space-time.
Steady State Concept by Hoyle (now less favored).
Star Formation
Initial density differences caused gravitational attraction.
Galaxies formed from hydrogen gas clouds (nebula).
Stars began forming 5-6 billion years ago.
Light Year:
A measure of distance, not time.
Light travels at 300,000 km/second.
One light year equals 9.461×1012 km.
Earth to Sun distance is 8.311 minutes in light years.
Formation of Planets
Stages in the development of planets:
(i) The stars are localized lumps of gas within a nebula.
The gravitational force leads to the formation of a core and a rotating disc of gas and dust around it.
(ii) The gas cloud starts condensing and matter around the core forms into small-rounded objects called planetesimals.
Collision and gravitational attraction lead to the growth of larger bodies.
Planetesimals are a large number of smaller bodies.
(iii) The planetesimals accrete to form fewer larger bodies in the form of planets.
Our Solar System
Our solar system consists of:
The sun (the star), 8 planets, 63 moons, millions of smaller bodies (asteroids, comets), and huge quantities of dust-grains and gases.
The solar system formed from a nebula that started collapsing about 5-5.6 billion years ago and formed the planets around 4.6 billion years ago.
Types of planets:
Inner Planets: Mercury, Venus, Earth, and Mars — located between the sun and the asteroid belt.
Outer Planets: The remaining four planets are gas giants.
Terrestrial Planets (Earth-like): Made of rock and metals, with relatively high densities.
Jovian Planets (Gas Giants): Larger, with thick atmospheres mostly of helium and hydrogen.
Pluto: Once considered a planet, it was reclassified as a dwarf planet by the International Astronomical Union in August 2006.
Why are the inner planets rocky while the outer ones are gaseous?
(i) The terrestrial planets formed close to the sun where it was too warm for gases to condense, whereas jovian planets formed farther away.
(ii) Intense solar winds near the sun blew off gases and dust from the terrestrial planets.
(iii) Terrestrial planets are smaller, and their lower gravity could not hold escaping gases.
The Moon
The moon is the only natural satellite of the Earth.
Early Theories of the Moon's Formation:
In 1838, Sir George Darwin suggested that Earth and the Moon were once a single rapidly rotating body that later broke apart.
Another theory suggested that the material forming the moon was separated from the Earth's Pacific Ocean.
Current Belief: The moon formed as a result of a giant impact or "the big splat":
A body 1-3 times the size of Mars collided with Earth shortly after its formation.
The collision blasted a large part of Earth into space, which later accreted to form the moon about 4.44 billion years ago.
Data Regarding Our Solar SystemPlanetary data of the solar system, illustrating the environmental factors influencing each planet and their balance within the system.
Distance from the Sun (in Astronomical Units):
Mercury: 0.387 AU
Venus: 0.723 AU
Earth: 1.000 AU
Mars: 1.524 AU
Jupiter: 5.203 AU
Saturn: 9.539 AU
Uranus: 19.182 AU
Neptune: 30.058 AU
Density (in gm/cm3):
Mercury: 5.44
Venus: 5.245
Earth: 5.517
Mars: 3.945
Jupiter: 1.33
Saturn: 0.70
Uranus: 1.17
Neptune: 1.66
Radius (in Earth radii):
Mercury: 0.383
Venus: 0.949
Earth: 1.000
Mars: 0.533
Jupiter: 11.19
Saturn: 9.460
Uranus: 4.11
Neptune: 3.88
Number of Satellites:
Mercury: 0
Venus: 0
Earth: 1
Mars: 2
Jupiter: about 53
Saturn: about 53
Uranus: about 27
Neptune: about 13
Evolution of the Earth
Initially, Earth was a barren, rocky, and hot object with a thin atmosphere of hydrogen and helium.
There were processes that caused Earth to evolve into a planet with ample water and a conducive atmosphere for life.
The Earth has a layered structure, with different zones containing materials of varying characteristics.
How was the Layered Structure of the Earth Developed?
The Earth was mostly in a volatile state during its primordial stage.
Gradual increase in density led to an increase in temperature, causing material separation based on density.
Heavier materials, like iron, sank to the center, while lighter ones moved towards the surface.
As the Earth cooled, it solidified and formed a crust, creating the outer layer of the Earth.
During the formation of the moon, the Earth was heated further, aiding the process of differentiation, leading to the formation of layers such as the crust, mantle, outer core, and inner core.
Evolution of Atmosphere and Hydrosphere
The Earth's atmosphere is mainly composed of nitrogen and oxygen.
There are three stages in the evolution of the atmosphere:
First Stage: Loss of primordial atmosphere (hydrogen and helium) due to solar winds.
Second Stage: The Earth's hot interior contributed to the evolution of the atmosphere.
Third Stage: The atmosphere was modified by life forms through photosynthesis.
Early Earth’s atmosphere, primarily hydrogen and helium, was stripped by solar winds.
During Earth's cooling, gases and water vapor were released, starting the evolution of the current atmosphere through degassing.
Continuous volcanic eruptions contributed water vapor and gases to the atmosphere.
As Earth cooled, water vapor condensed into rain, forming oceans within 500 million years.
By 3,800 million years ago, life began to evolve in the oceans.
Around 2,500-3,000 million years ago, photosynthesis evolved, contributing oxygen to the oceans and atmosphere.
By 2,000 million years ago, oxygen began to flood the atmosphere, altering its composition.
Geological Time ScaleThe geological timescale, depicting Earth's history through various periods and epochs, showing the evolution of life and the planet.
Quaternary (0 - 10,000 years): Modern Man
Holocene: 0 - 10,000 years
Pleistocene: 10,000 - 2 million years
Tertiary (2 - 65 million years): Early Human Ancestor
Pliocene: 2 - 5 million years
Miocene: 5 - 24 million years
Oligocene: 24 - 37 million years
Eocene: 37 - 58 million years
Palaeocene: 57 - 65 million years
Mesozoic (65 - 245 million years): Mammals
Cretaceous: 65 - 144 million years
Jurassic: 144 - 208 million years
Triassic: 208 - 245 million years
Palaeozoic (245 - 570 million years)
Permian: 245 - 286 million years
Carboniferous: 286 - 360 million years
Devonian: 360 - 408 million years
Silurian: 408 - 438 million years
Ordovician: 438 - 505 million years
Cambrian: 505 - 570 million years
Proterozoic (570 - 2,500 million years): Soft-bodied arthropods.
Archean (2,500 - 3,800 million years): Blue-green algae and unicellular bacteria.
Hadean (3,800 - 4,800 million years): Oceans and continents form, rich in carbon dioxide.
Origin of Life: Life began to evolve around 3,800 million years ago.
Origin of Life
Life evolved through a chemical reaction that generated complex organic molecules capable of duplication.
Fossils provide evidence of life that existed on Earth in different periods.
Microscopic structures related to blue-green algae have been found in geological formations older than 3,000 million years.
Life likely began evolving around 3,800 million years ago.
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