Origin of the Earth [Book Review]

Lord Kelvin calculated that Earth began to solidify 40 million years ago, thus starting a long-time confrontation between geologists and "natural philosophers." Following the discovery of radioactivity, Earth was viewed as having a cold, tranquil beginning. The Schmidt-Safranov accretional theory gave long accretion times, 10^8 years, for Earth. Gravitational energy radiated away, and planets formed in an unmelted condition. In standard geological models, the planet heated up gradually as a result of the decay of radioactive elements. Much later the "core formation event" heated and differentiated Earth. However, it has long been clear to some earth scientists that early Earth was hot and that an origin involving extensive melting was unavoidable. The Hanks-Anderson rapid-accretion hypothesis implied a hot origin, with differentiation and core formation simultaneous with accretion. This book continues the debate.