Origin and evolution of earth’s crust

I. THEORIES OF ORIGIN OF EARTH

Nebular Hypothesis: The Nebular Hypothesis proposes that the Earth and other celestial bodies originated from a nebula, which is a cloud of dust and gases. There are two main theories within the Nebular Hypothesis:

1. Monistic Theory: This theory was proposed by E. Kant in 1750. According to the Monistic Theory, the nebula gradually condensed and formed all the heavenly bodies we observe today.

2. Nebular Accretion Theory: Laplace provided a more convincing explanation for the Earth’s layered structure. The Nebular Accretion Theory suggests that the nebula gradually accreted and formed the different layers of the Earth.

Planetesimal Theory: Based on the Binary/Dualistic Theory proposed by Chamberlain and Moulton, the Planetesimal Theory suggests that the Earth originated from two bodies: the protosun and an intruding star. These bodies coalesced to form the Earth.

Tidal Theory: The Tidal Theory, based on the Binary/Dualistic Theory proposed by Jean and Jeffrey, explains the arrangement of the planets in the solar system. According to this theory, a cigar-shaped mass or filament extended from the protosun. This filament coalesced to form the planets of our solar system.

Capture Hypothesis: Proposed by Michael Mark Woolfson, the Capture Hypothesis states that the planets were not only formed from the filament ejected from the protosun but also from some matter ejected from the intruding star. This hypothesis explains why the outer planets (Jovean Planets) are gaseous, originating from the filament of the intruding star, while the inner planets are terrestrial, originating from the filament of the protosun.

Binary Star Theory: The Binary Star Theory suggests that there are two binary star systems rotating around a common center of mass. This theory, known as the Trihybrid Theory proposed by Russell, indicates the presence of binary star systems in the universe.

Interstellar Dust Hypothesis: According to Schmidt’s Interstellar Dust Hypothesis, the origin of the Earth is not solely from a nebula but also from dust and gases known as interstellar dust.

Catastrophic Theory: Based on the Supernova Theory proposed by Hoyle, the Catastrophic Theory suggests that in a binary star system, one of the stars undergoes a violent explosion. The matter ejected from this explosion coalesces to form planets that revolve around the other star of the binary system.

Big Bang Theory: The Big Bang Theory, initially proposed by Lemaitre and refined by Admen Hubble, explains that the universe is expanding. It suggests that the universe began with a cosmic singularity explosion, where all mass and time originated. This event occurred approximately 13.5-15 billion years ago.

II. EVOLUTION OF EARTH (Timeline)

HADEAN: During the Hadean era, there was no life and no atmosphere on Earth.

ARCHEAN/ARCHEAZOIC: The Archean era marks the appearance of the first life on Earth, specifically cyanobacteria.

PROTEROZOIC: During the Proterozoic era, various life forms emerged, including jellyfish and trilobites. This era encompasses approximately 90% of Earth’s history during the Precambrian phase.

Cambrian Explosion: The Cambrian Explosion was a period characterized by the rapid diversification and emergence of various life forms.

PHANEROZOIC (Visible life forms):

• Coeno/Cainozoic Era: The Coenozoic era, also known as the Age of Mammals, is associated with the formation of the Himalayas, Rockies, and Andes mountain ranges.
  • PERIODS:
    • Quaternary: This period includes the Holocene and Pleistocene epochs.
    • Tertiary: This period includes the Pliocene, Miocene, Oligocene, Eocene, and Paleocene epochs.
• Mesozoic Era: The Mesozoic era, known as the Age of Reptiles, witnessed the dominance of reptilian life forms.
  • PERIODS:

• • • Cretaceous
    • Jurassic
    • Triassic
• Palaeozoic Era: The Palaeozoic era was characterized by the Caledonian and Hercynian mountain-building events.
  • PERIODS:
    • Age of Amphibians: This period includes the Permian epoch.
    • Major extinction phase: The Carboniferous period marked a significant extinction event.
    • Age of Fishes: This period includes the Devonian and Silurian epochs.
    • Age of Invertebrates: This period includes the Ordovician and Cambrian epochs.