![]() As a result the shape of the Earth became increasingly distorted until part of it fissioned off. ![]() Because moment of inertia is proportional to angular acceleration this caused the Earth to rotate faster (with a rotational period of about 2.1 hours) and this made the Earth rotationally unstable. As differentiation of the core and mantle occurred there was a decrease in the Earth's moment of inertia because there was more mass focused towards the center of the planet. The Fission Theory of rotational instability was based on a model that estimated the early Earth to have a rotational period of 2.6 hours (just inside the rotational stability field) and a uniform density throughout the planet. in its early molten or semi-molten state the rapid rotation distorted the shape of the planet and part of the planet was thrown off and then accreted to form the Moon (see Figure 1). Subsequent experiments in the 1930s disproved Darwin's theory saying that based on his calculations, the amount of tidal distortion that resulted from the angular momentum he proposed was not significant enough to fission a Moon sized object. Follow up investigations in the 1960s however, revived the idea of fission as a legitimate theory for Moon formation.įission Theory was revived in the 1960s because scientists investigated rotational instability as a mechanism for fission of the Moon whereas Darwin had envisaged the Earth having a constant fast spin.Īt the most basic level Fission Theory states that very early in Earth history the Earth was spinning many times faster than it does today. Darwin's calculations of how much angular momentum the Earth needed to have to fission off an object the size of the Moon were very accurate however his theory was flawed on the grounds that he had little scientific evidence to back up his hypothesis. The Fission Theory of the formation of the Moon was proposed much earlier than the Impact Theory and was proposed originally by George Darwin (son of Charles Darwin) in 1879.
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