Answers to Everyday Questions : What is the history of the earth ?

Around 4.6 billion years ago, the planet Earth was formed in a completely molten state. Sometime around the earth’s formation, a smaller planet named “Theia” has been thought to have formed in the same manner as it orbits around the newly-formed Sun. However, this Mars-sized planet suffered from impact on the Earth due to orbital oscillations, which resulted in ejecting large amounts of crusts that formed the moon. Today, this theory of the moon formation has been widely known as the “Giant Impact Hypothesis” and remains the most current theory available.

The history of the Earth began around 3.8 billion years ago. This first era, which extended from the Earth’s formation, was called “Hadean Eon” from the Greek mythology Hades. During this era, the oceans began to form while the Earth cooled down from its molten state, which resulted in forming a solid crust for about 125 million years. Since the Earth was starting to melt down, heavy elements like nickel and iron sank to the Earth’s core, leaving only small amounts on the surface. The Earth experienced being divided into layers during the mid-Hadean Eon. By the later part of this era, primitive life emerged.

The next history of the Earth was recorded to last about 1.3 billion years and was called the Archean Eon. Studies have shown that the around 3.5 billion years ago in early Archean, the ‘last universal common ancestor’ of contemporary life existed and the first autotrophs evolved on Earth. These autotrophs are organisms that have the ability to use photosynthesis in extracting energy from the Sun. Since photosynthesis releases oxygen, which poisoned living organisms then, and was believed to be released in large quantities during this era, a mass extinction occurred. This extinction, which is now called the ‘Oxygen Catastrophe’ reshaped the surface and atmospheric chemistry of the Earth.

Other eras following the Archeon Eon included the “Primitive Era of Life” (Proterozoic Eon), the “Old Era of Life” (Paleozoic Eon), the “Middle Era of Life” (Mesozoic Eon), and the “Recent Era of Life” (Cenozoic Eon). However, it was only about 540 million years ago did the complex multi-cellular life evolved.