What is the History of the Earth?
The planet Earth formed about 4.6 billion years (4,567,000,000 years) ago, in a fully molten state, from the protoplanetary debris disc orbiting the newly formed Sun. Another, smaller Mars-sized planet, called Theia, is thought to have formed in the same orbit as the Earth around this time. After 28 – 34 million years (4.527 – 4.533 billion years ago), orbital oscillations caused Theia to impact the Earth, ejecting a large amount of crust and forming the Moon. That is the best current theory of the Moon’s formation, called the Giant impact hypothesis. The first era in the history of the Earth is known as the Hadean Eon (named after the underworld of Greek mythology, Hades), which extends from the Earth’s formation to 3.8 billion years ago. The oceans began forming during the first part of the Hadean, possibly as long as 4.2 million years ago. The Earth cooled from a molten state, forming a solid crust within just 100 – 150 million years. Heavier elements such as iron and nickel sank to
