Theories: Origin and Evolution of the Earth
The Origin of Earth
The origin of Earth dates back approximately 4.54 billion years. Initially, Earth was a barren, rocky, and hot object with a thin atmosphere composed of hydrogen and helium. The present composition of Earth’s atmosphere includes nitrogen and oxygen.
Various scientists, philosophers, and scholars have played a significant role in shaping early ideologies about the origin of Earth:
(a) Thales: He presented a scientific explanation, moving away from mythological beliefs. According to his monotheistic theory, all things originate from water, and eventually, they dissolve in water.
(b) Anaximenes: He proposed that everything in the world originated from air. According to his belief, air is infinite, transforms into fire, becomes liquid, solidifies into water, and ultimately turns into Earth.
(c) Pythagoras: He suggested that all matter in the world is limited. Despite their differences, all substances represent one form, and no single substance is considered the sole cause of the world’s origin.
(d) Heraclitus: According to him, fire (agni) is the fundamental cause of the world’s origin. Water and Earth emerged from fire, and these elements are dynamic and transient, with nothing permanent in the world.
Theories of Origin of Earth
Various hypotheses/theories related to the origin of Earth were presented by various modern and scientists. Some of the important hypotheses have been described below.
| Hypothesis | Explanation |
| Dualistic Hypothesis | Involves the interaction of two heavenly bodies. |
| Modern Hypothesis | A contemporary approach to understanding the origin of Earth. |
| Monistic Concept | Involves only one heavenly body in the origin process. |
| Comet Hypothesis (1749) | Proposes the role of comets in Earth’s formation. |
| Gaseous Hypothesis (1755) | Suggests the formation of a gaseous cloud. |
| Fission Theory (1878) | Proposes Earth’s separation from the Sun through fission. |
| Nebular Hypothesis (1796) | Involves the condensation of a nebula into Earth. |
| Meteoritic Hypothesis (1919) | Considers meteorites as contributors to Earth’s formation. |
| Binary Star Hypothesis (1937) | Involves the interaction of binary stars in Earth’s formation. |
| Big Bang Theory (1931) | Suggests Earth’s origin from the aftermath of a big bang. |
| Cosmic Inflation Theory (1980) | Describes the rapid expansion of the universe after the Big Bang. |
| Interstellar Dust Hypothesis (1943) | Proposes the role of interstellar dust in Earth’s formation. |
| Planetesimal Hypothesis (1905) | Suggests the aggregation of small planetesimals to form Earth. |
| Tidal Hypothesis (1919) | Considers tidal forces in Earth’s formation process. |
| Supernova Hypothesis | Proposes the involvement of supernova explosions in Earth’s origin. |
(A) Monistic Concept (Parental Hypothesis)
Advocates of the Monistic Concept propose that all planets originated from the same celestial object or body.
Various scholars have presented diverse ideas about the solar system’s origin, suggesting a single-star origin. Key hypotheses associated with the Monistic Concept include:
(a) Comet Hypothesis
Proposed by Georges Louise Leclerc in 1749, this hypothesis suggests that a comet collided with the Sun, resulting in fragments that later formed the planets.
Considered the initial version of the cataclysmic hypothesis for the solar system’s origin.
Georges Louise Leclerc mistakenly assumed comets could be nearly as large as stars.
(b) Gaseous Hypothesis
Introduced by German philosopher Immanuel Kant in 1755, this theory posits the existence of divinely created matter particles in the universe.
These particles, initially hard, cold, and motionless, collided due to gravity, generating heat and motion.
Small particles fused into larger bodies, ultimately forming a giant gaseous body called Nebula.
The high rotational speed of Nebula led to increased heat, causing the centrifugal force to surpass the centripetal force.
Circular rings formed, cooled down, and transformed into planets, while the remaining nebula evolved into the Sun over millions of years.
(c) Nebular Hypothesis
Described by French scholar Laplace in 1796, the Nebular Hypothesis presents a hot, slow-moving superbody in the universe known as a nebula.
Over time, the nebula continuously cooled, contracting and reducing in size and volume.
Increased rotational speed led to a balance shift between centrifugal and gravitational forces.
A ring detached from the nebula, breaking into smaller rings that, upon cooling, evolved into planets and satellites.
Later, the French scholar Ross made modifications to Laplace’s hypothesis. According to Ross, multiple rings gradually separated from the nebula, and each ring condensed to give rise to a planet. The continuous movement in a sequence led to the origin of all planets.
(d) Meteoritic Hypothesis
Proposed by Russian scientist Otto Schmidt in 1944, this hypothesis suggests that the Earth and other solar system planets formed from interstellar matter clusters captured by the Sun during its passage near the galactic center.
Schmidt substantiated the regularity in the distance between planets, their mass, and their density distribution.
(e) Dualistic Hypothesis
The proponents of this ideology believed that the planets originated from the combination of two stars. Therefore, this concept is also known as the Bi-parental concept. Theories developed under this concept are given below
(B) Fission Theory
George Howard Darwin proposed the fission theory in 1878, suggesting that the Moon was once part of the Earth, separating early in the solar system’s history.
The present Pacific Ocean basin is considered a likely site for the part of the Earth from which the Moon originated.
(C) Planetesimal Hypothesis
Proposed by Chamberlin and Moulton in 1905, this hypothesis suggests that the solar system’s planets formed from a collision between the Sun and another star.
Small particles, known as granules, emerged from the Sun’s surface due to gravitational forces, revolving around the Sun and later condensing into planets.
(D) Tidal Hypothesis
Sir James Jeans proposed this hypothesis in 1919 to explain Earth’s origin.
Harold Jeffreys modified the tidal hypothesis in 1929 for increased relevance. According to this hypothesis, the Sun was once a gaseous mass, and an intruding star, larger than the Sun, came close.
Tidal forces damaged the intruding star on the primitive Sun’s surface, ejecting matter that became the building material for future planets.
(E) Binary Star Hypothesis
Russell and Littleton proposed the binary star hypothesis in 1937, suggesting that the Sun was not initially the only star; two others were present.
The Sun and its companion star revolved around the same center, and a third star’s approach increased the gravitational force and attraction between them.
Material from the companion star circled the giant stars, forming planets and later satellites when solidified.
(F) Supernova Hypothesis
Fred Hoyle and Littleton presented this hypothesis in 1939, stating that planets originated from the explosion of a companion star of the Sun involving three stars.
The explosion of the companion star led to the scattering of dust particles and gases, which eventually coalesced around the Sun, forming the planets.
(G) Interstellar Dust Hypothesis
Otto Schmidt proposed this hypothesis in 1943. According to the theory, when the Sun passed near the Milky Way, gaseous clouds and dust particles were attracted by the Sun’s gravitational force, orbiting around it.
Initially, gas and dust particles moved separately in a disorganized manner. The dust, present in larger quantities, condensed into a flat plate, forming planets and satellites through multiple stages of condensation.
The hypothesis suggests that dark matter in the universe exists in the form of gas and dust clouds, possibly originating from meteors and stars.
(H) Modern Hypothesis
Modern theories seek to understand the formation of the universe, going beyond the evolution of Earth and planets. Various modern hypotheses are discussed below.
(I) Big Bang Theory
Georges Lemaitre proposed the Big Bang theory in 1931, suggesting that all matter in the universe was once concentrated in a tiny space with high temperatures.
Robert Wagoner elaborated on this theory in 1967, following Edwin Hubble’s evidence of the expanding universe. The Big Bang theory posits that the universe began about 13.7 billion years ago in a massive expansion.
The creation of substances after the explosion formed various objects, leading to the formation of galaxies over time. Fission in galaxies may have produced stars, and fission in stars may have produced planets.
The Steady-State theory, an alternative to the Big Bang, was developed by Fred Hoyle in 1948, suggesting a continuous creation of matter to maintain the density of the expanding universe. However, it didn’t gain widespread acceptance.
(J) Cosmic Inflation Theory
Alan Harvey Guth proposed the Cosmic Inflation theory in 1980, suggesting that the early universe experienced rapid exponential expansion for a brief period after the Big Bang.
This theory gained support with the discovery of gravitational waves, reinforcing the inflation model of cosmology.
Evolution of Earth
With an estimated age of around 4.54 billion years, the Earth’s origin was first hypothesized by the French scientist Comte De Buffon in 1749 AD.
Initially, Earth existed as a barren, rocky, and hot entity with a thin atmosphere of hydrogen and helium. Oxygen emerged significantly later with the advent of floral species engaging in photosynthesis.
Over time, the Earth transformed into a vibrant planet with abundant water and a hospitable atmosphere conducive to life.
The Earth exhibits a layered structure, with materials varying in density from the center to the upper atmosphere.
The lithosphere represents the Earth’s land portion, while the hydrosphere encompasses the water elements.
Life is believed to have originated around 3,800 million years ago, primarily confined to the oceans. The initial phase witnessed the evolution of microscopic organisms similar to blue-green algae.
Subsequent developments included the emergence of fishes, amphibians, reptiles, flowering plants, mammals, and, finally, Homo sapiens.
