The Origin of Planet Earth

Otto Yulyevich Schmidt

  • The Accretion Theory that Earth and the other terrestrial planets formed from meteoric material was proposed in 1944

    • This theory he published in his 1949 book Four lectures on the theory of the origin of the Earth

Accretion

  • One of the leading scientific idea for the formation of planet Earth

  • it is a process that occurs when gravity attracts tiny bits of matter towards an object.

Condensation

  • the process of forming solid particles from the solar nebula, to form the entire solar system, including the sun and planets.

Sequences of Events

  1. The collapse of molecular cloud

    • a portion of a molecular cloud collapses to form a star and a protoplanetary disk, while more dust condenses from the gas phase within the disk

  2. The formation of the protoplanetary disc

    • dominated by gravity from the star and aerodynamic forces from the gas, including turbulence

  3. the growth of planetesimals

    • Aerodynamic forces remain dominant until bodies grow to 1- 100 km in size. Such bodies, referred to as planetesimals

    • Small particles also physically embed themselves in larger aggregates during high-speed collisions

  4. Begin to orbit the central star

    • their subsequent evolution is dominated by mutual gravitational interactions and collisions as they orbit the central star

  5. The growth of the protoplanet Earth

2 Types of Accretion

  1. Homogeneous

    • It is when Earth accreted from materials of the same composition after condensation

  2. Heterogeneous

    • It is when Earth accreted during condensation, forming a differentiated planet as it grew in size