In the violent beginnings of our planet the surface of the Earth looked a terrifying place. White-hot magma, formed of molten rock from the Earth’s interior, boiled on the surface with constant explosions. At the same time showers of meteorites and cosmic dust, attracted by the pull of the Earth’s gravity, made the sphere grow bigger and bigger as it rotated in space.
Huge spirals of gas and water vapour rose out of the magma to darken the sky and keep the light of the Sun from failing on to the Earth. The gloom of the night was continually shattered by flashes from the explosions and eruptions of the Earth’s surface.
Millions of years passed before the first islands of rock, derived from cooled magma, appeared on the sea of lava. As it solidified, the white-hot magma, which formed the Earth in the beginning, gave rise to a basic rock type known as igneous (from the Latin ignis, meaning fire). There is little trace left of these rocks today, however, at least on the surface: corroded and wasted away by the forces present in the atmosphere, they have been transformed into gravel, sand and dust.
These substances, washed away into the large sea-basins by rivers and floods, have been deposited there in layers. The weight of the upper layers exerted tremendous pressure on those beneath, squeezing out the water and then cementing the fragments together again, forming new rocks. By the action of intense natural forces, they have then undergone other fundamental changes. The layers, or strata, have been folded, curved or broken. The distorted layerings of the rocks on our mountains give some idea of what happened to the Earth’s crust.