Origin and Evolution of Earth is a fascinating subject that delves into the beginnings of our planet, tracing its journey from the formation of the universe to the development of life. In order to understand Earth, which is the prime focus of Geography as a discipline, we must first comprehend its origin.
However, to achieve this, we must first understand the origin of our solar system and the Universe in general. There are various theories that provide a basis for the origin of the Universe.
Early Theories
The earliest hypothesis, which is now rejected, shows the imagination of the early philosophers.
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Nebular Hypothesis
Planets were formed out of a cloud of material associated with the youthful sun, which slowly started rotating. It was given by Immanuel Kant, a German Philosopher in 1755. Pierre Simone Laplace, a mathematician, revised the Nebular Hypothesis in 1796.
Chamberlain and Mouton (1900) predicted that a wandering star once approached the sun in its initial stages of formation, which created a cigar-shaped extension of material separated from the solar surface. These then formed planets.
Otto Schmidt from Russia and Carl Weizascar from Germany also favored a Nebular Hypothesis but with differing details. According to them, a solar nebula containing Hydrogen and Helium along with ‘dust’ first existed. The friction and collision of particles led to the formation of disk-shaped clouds, and planets were formed through a process of accretion.
These hypotheses improved with a better understanding of the structure of the Sun but never satisfactorily explained the origin of Earth.
Modern Theories
The modern theories are based on scientific understanding of the origin of the Universe.
The Expanding Universe Hypothesis
An astronomer named Edwin Hubble in 1929 studied the Cepheids in Andromeda Galaxy to analyze their luminosity. Cepheids are pulsating stars that have a constant range of luminosity, which can be used as a standard to measure the brightness of other celestial objects. Using this method, Edwin Hubble calculated the distance of each Cepheid from Earth. In 1929, he noted that these objects were not emitting their true color but were slightly red-shifted, confirming that the universe was expanding.
What is a Red-Shift?
When a celestial object moves away from us, its wavelength increases, making the object appear redder. The wavelength of such objects can even expand so much that the object might be visible only through infrared waves or microwaves. The faster the object recedes, the greater the redshift.
Not only is the universe expanding, but observations of Type Ia supernovae show that this expansion is accelerating.
The Big Bang Theory
Given the premise that every celestial object is accelerating away from each other, then, at one point in time, the Universe must have been much smaller and possibly originated from a single point.
With the help of expansion rate calculations, scientists estimate that the Universe originated around 13.8 billion years ago. From this point, a giant explosion took place, initiating the continuous expansion of the Universe.
Stages of Development of the Universe
On the basis of calculations based on the theory of relativity and quantum physics, the following stages of the Universe’s development have emerged:
- Beginning: Around 13.8 billion years ago, a “tiny ball” with an unimaginably small volume, infinite temperature, and infinite density exploded.
- Big Bang: The explosion continues even today. A rapid expansion happened within fractions of a second after the Big Bang, which later slowed down.
- Sub-atomic Particles: A millionth of a second after the Big Bang, the first sub-atomic particles appeared. However, for a few seconds, it was so hot that sub-atomic particles could not bind together to form atoms.
- Formation of Atoms: Within the first 3 minutes, the first atoms began to form, allowing light to pass through for the first time, creating the cosmic background radiation still observable today.
- Atomic Matter: Only after 300,000 years did the temperature drop below 4,500K, giving rise to stable atomic matter, making the universe fully transparent.
Formation of Stars and Galaxies
The initial density of the first-formed atomic matter led to differences in gravitational forces, causing matter to clump together under the influence of gravity, forming galaxies and stars.
Formation of Stars
Stars are formed by the accumulation of hydrogen gas in large clouds called nebulae. These clouds attract nearby gas clouds, grow denser, and develop localized clumps of gas, giving rise to the formation of stars.
Star Destruction
A star can be destroyed in one of two ways:
- Supernova Explosion: Occurs when a massive star (greater than 1.4 times the solar mass) dies and explodes.
- Formation of Neutron Stars and Black Holes: Some remnants from supernova explosions turn into neutron stars, while others collapse further into black holes.
Our Solar System
The Sun was formed around 5-6 billion years ago from a dust cloud known as the Solar Nebula. The gravitational forces within this nebula led to the formation of a core, accompanied by a huge rotating disc of gas and dust. Over time, planetesimals formed, eventually accreting into planets.
Formation of Planets
Our Solar System consists of eight planets, 63 moons, and millions of smaller celestial bodies, including asteroids and comets.
- Inner (Terrestrial) Planets: Mercury, Venus, Earth, and Mars—rocky planets with thick atmospheres.
- Outer (Jovian) Planets: Jupiter, Saturn, Uranus, and Neptune—gas giants with thick hydrogen and helium atmospheres.
Formation of the Moon
The Moon formed around 4.4 billion years ago due to a giant impact. A Mars-sized body collided with Earth, ejecting material that eventually coalesced into the Moon.
Evolution of Earth
Development of Lithosphere
Earth formed around 4.6 billion years ago. Initially in a molten state, it gradually cooled, allowing heavier metals to sink and forming the Earth’s core, mantle, and crust.
Evolution of Atmosphere and Hydrosphere
- Primordial Atmosphere Loss: Hydrogen and Helium were stripped away by solar winds.
- Degassing: Volcanic eruptions released gases, forming a secondary atmosphere.
- Formation of Hydrosphere: As Earth cooled, water vapor condensed into oceans.
- Photosynthesis: Around 2.5-3 billion years ago, photosynthesis began producing oxygen.
Origin of Life
Life likely began around 3.8 billion years ago as a chemical reaction forming complex organic molecules. The fossil record shows microscopic life dating back over 3,000 million years.
Stanley Miller’s Primordial Soup Hypothesis
In 1953, Stanley Miller conducted an experiment simulating early Earth’s atmosphere. He found that basic organic molecules, such as amino acids, could form under these conditions.
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FAQs related to Origin and Evolution of Earth
1. How old is the Earth?
Earth is approximately 4.6 billion years old.
2. What is the Big Bang Theory?
It is the theory that the universe originated from a single point around 13.8 billion years ago through a massive explosion.
3. How did the Moon form?
The Moon formed due to a giant impact between Earth and a Mars-sized body.
4. When did life first appear on Earth?
Life likely began around 3.8 billion years ago in Earth’s oceans.
