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The Earth’s crust formed 4.44 billion years ago, 100 million years after the formation of the Earth. The Iron Catastrophe caused denser elements to sink into the core, while lighter elements formed the crust. The Hadean era was lifeless, and the Late Heavy Bombardment may have prevented the creation of long-lived continents. Photosynthetic life evolved 2.7 billion years ago, creating an oxygen atmosphere and silicon dioxide making up most of the Earth’s crust today.
The earth’s crust, its outermost layer, formed about 4.44 billion years ago, about 100 million years after the formation of the earth itself. Prior to 4.44 billion years ago, the Earth’s crust was completely molten, due to residual heat from the planet’s initial collapse. Evidence that the earth’s crust cooled within 100 million years comes from measurements of hafnium levels in Jack’s Hills in Western Australia, one of the oldest areas of crust exposed today.
During the initial formation of the Earth’s crust, an event known as the Iron Catastrophe occurred, in which denser elements of the Earth’s composition, such as iron and nickel, sank into its core, while lighter elements, such as silicon, formed a crust at the top.
The crust began to cool when the Earth was at least 40% of its current size, possessing sufficient gravity to hold onto an atmosphere containing water vapor. Much of this early water vapor would have come from comets. This era in Earth’s history, spanning from Earth’s birth to approximately 3.8 billion years ago, is known as the Age of the Hadean, from the Greek Hell, Hades, due to the difficult conditions on the planet at the time . Scientists believe that the era of Hadean was lifeless.
From 4.0 to 3.8 billion years ago, near the end of the Hadean era, the planet experienced Late Heavy Bombardment, a time period with many large asteroid impacts. These impacts may have literally shattered the virgin earth’s crust, preventing the creation of long-lived continents. In practice, looking back beyond 3.8 billion years ago is difficult, as the oldest rock formations date from this age. The only terrestrial minerals older than this are individual rocks and crystals, which give less information about the global state of the earth’s crust at the time.
About 2.7 billion years ago, photosynthetic life evolved. It released huge amounts of oxygen, isolating it from the water in the process of photosynthesis. The Earth created an oxygen atmosphere and the oxygen began to bind with most of the elements on the surface, creating huge amounts of oxides. Today, most of the earth’s crust is made up of silicon dioxide.
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