4.54 billion years ago Hadean- The age of Chaos
Some 200 million years after a molecular cloud of hydrogen and helium came together to form the Sun, the primordial Earth formed from some of the heavier elements that made up the protoplanetary disk left behind.
Bound by gravity, the leftover stardust from the Sun’s creation also formed the rest of the planets in our solar system. The inner solar system was a violent and crowded place during which the Earth was repeatedly pelted with rocks from outer space. The surface was young and volatile as molten rock covered a globe utterly void of life.
Highlights of the Hadean
- Chaos gives birth to Gaia
- Formation of the Moon
- Meteoric bombardment
- Emergence of plate tectonics and continents
- Formation of the first and second atmospheres
- Creation of the oceans
Earth formed in this manner about 4.54 billion years ago and was largely completed within 10–20 million years.
The proto-Earth grew by by the gradual accumulation of additional matter each impact adding to its momentum until its interior was superhot causing most heavy metals to sink to its core . This so-called iron catastrophe resulted in the separation of a primitive mantle and a (metallic) core only 10 million years after the Earth began to form, producing the layered structure of Earth and setting up the formation of Earth’s magnetic field.
There is no life. Temperatures are extremely hot, with frequent volcanic activity and hellish environments. The atmosphere is nebular. The early oceans are bodies of ever changing molten liquid.
4.51 billion years ago The moon is formed due to a protoplanet’s collision into Earth.
The Lunar Cataclysm and the Birth of the Moon
The formation of the Moon is just one of many events, which occurred early in the history of our planet, that has had a profound influence on the evolution of life. Without it, there would have been no lunar tides, thus stifling the migration of life from the sea to the land billions of years later.
Radiometric dating of lunar samples have revealed that the Moon is almost as old as the Earth, only around 30 million years younger in fact. Formed by a colossal impact event between the young Earth and a Mars-sized planet, often dubbed ‘Theia’.
The Hadean aeon is largely characterised by a period known as the Late Heavy Bombardment, during which the young Earth and moon experienced countless impact events. Since the inner solar system was so crowded during these far-off times, the surface was constantly bombarded by asteroids.
During this period, the whole planet was covered by an ocean of lava dozens of miles deep. The violent, scorching surface was a product of the constant stream of impacts from outer space coupled with the energy being released from the formation of the Earth’s molten core. At its peak, the temperature was probably around 1,000 °C. Unsurprisingly, the atmosphere was completely different to what we’re used to breathing today. Instead of a healthy mix of nitrogen and oxygen, the Hadean air comprised mostly of hydrogen left over by the formation and accretion of the solar nebula. This early atmosphere stabilised over the course of the aeon as constant volcanic eruptions filled the skies with other gases, such as nitrogen and carbon dioxide. Eventually, most of the lighter gasses that made up the early atmosphere escaped from Earth’s gravity, allowing heavier elements to take their place.
Land Masses Rise from the Magmatic Ocean
The early stages of the Late Heavy Bombardment ended around 4.5-billion years ago as the Sun evolved to become the main-sequence star that we see today. The solar wind helped to clear Earth’s orbit of dust and gas and the violent birth of the solar system gave way to a relatively calmer period that pervades to this day and will continue for at least the next billion years. As the dust settled and the apocalypse drew to an end, the surface started to cool enough for continents to form. Out of the fiery depths of what is now the mantle, a solid crust formed and, finally, our world had a surface that you could stand on.
The first oceans on Earth also formed during the Hadean aeon. Nonetheless, they would have been very different to what we know today. With surface temperatures estimated to be over 200 °C, liquid oceans could only exist without vaporising due to the much higher atmospheric pressure combined with an extremely heavy greenhouse effect. Eventually, the evolution of plate tectonics hailed in a new geological aeon by trapping a large portion of these greenhouse gasses inside the Earth and allowing the surface to cool.