How Has the Earth Evolved? main content.

How Has the Earth Evolved?

Part of Hall of Planet Earth.

Greenland Isua sequence

Rocks Tell the Earth's Story

The continental crust contains the historical record of our planet. Its most ancient rocks are four billion years old, and the youngest ones are still forming today. Parts of the continental crust may be older than four billion years, but if so, they are not exposed, or have not been found, on the Earth’s surface. The rocks of the crust convey the story of how the planet has been transformed between the period shortly after its formation and the way we see it today.

How Did the Earth Form?

The Sun and its family of planets formed when a cloud of dust and gas condensed 4.6 billion years ago. Several hundred million years after the Earth took form, an outer crust developed. But these surface rocks are no longer available for study: they have disappeared into the interior of our dynamic planet. Our only clues to how the Earth formed come from meteorites and the Moon because both formed simultaneously with the planets.

What Is the Earth Made Of?

The great bulk of our planet is composed of oxygen, iron, silicon, and magnesium. Since the Earth formed relatively close to the Sun by the aggregation of smaller solid bodies, it is a rocky, solid planet whose atmosphere formed later. The more remote, giant gas planets, from Jupiter to Neptune, formed predominantly from the lighter, more volatile elements, like hydrogen and helium.

Graphic depicting the early composition of the Earth: the planet's entire outer layer may have been molten.
As the Earth started to grow, about 4.56 billion years ago, the heavy iron sank to the center, and the lighter silicates rose to the surface. Heat generated from impacts of other bodies kept the early Earth molten. In fact, the planet’s entire outer layer may have been liquid, an idea that came from studying the Moon. Rocks of the lunar highlands are believed to have solidified from a similar ocean of molten rock, or magma. Unlike the Earth, the Moon is geologically inactive; thus, the cold, solid crust of its magma ocean still exists.
© AMNH
Pie chart depicting the Earth's composition: our planet is comprised mainly of oxygen, iron, silicon, and magnesium.
The great bulk of our planet is composed of oxygen, iron, silicon, and magnesium. Since the Earth formed relatively close to the Sun by the aggregation of smaller solid bodies, it is a rocky, solid planet whose atmosphere formed later. The more remote, giant gas planets, from Jupiter to Neptune, formed predominantly from the lighter, more volatile elements, like hydrogen and helium.
© AMNH