The Earth formed along with all the other planets around 4.5 billion years ago. The planets of our solar system formed shortly after the sun. After the formation of the sun, a vast disk of gas and dust called a protoplanetary disk formed in orbit around the sun. Gradually, material within the disk condensed into solid matter, forming small rocky objects called planetesimals. Over time, these objects collided with one another to form meteors and asteroids. Eventually, objects became massive enough that their gravitational pull began drawing in more material, forming the first planets, including a planet that would one day become Earth.
Making A Planet
For decades, planet formation was one of astronomy's biggest mysteries. Our solar system was the only known system of planets in the universe for a long period. Yet, as telescopes became more powerful, astronomers started discovering distant stars currently in the process of forming their own planets. Since we have no way of observing the formation of our solar system, scientists rely on studying other solar systems in the formation process to get an idea of how our solar system came to be.
The generally accepted model is that the Earth formed 4.5 billion years ago within a protoplanetary disk around the sun from the collision between countless particles of matter. The Earth of 4.5 billion years ago was far different than the planet we inhabit today. There was no solid surface, no oceans, and no life. Rather, the young Earth was completely molten, with a sea of magma enveloping the forming planet. Over a few hundred million years, however, the surface began to cool, and magma solidified to form the first crust. Volcanic eruptions were a constant on the young Earth's surface, yet the gasses emitted from so many eruptions led to the formation of Earth's first atmosphere.
As pressures began to stabilize on the surface, water vapor in the atmosphere could condense into liquid form, and after many millions of years, the first oceans started to appear. By about 3.8 billion years ago, the Earth was covered in water. Less than a billion years after its formation, the Earth had an atmosphere, and liquid water flowed across the surface.
Before the formation of any atmosphere or oceans, the Earth itself was nearly destroyed due to a catastrophic collision that occurred shortly after the planet's formation. While our solar system contains eight known planets today, this was not always the case. Rather, the early solar system may have contained as many as a hundred planets. Some of these planets were flung out of the solar system entirely, yet others collided with one another. It is likely that every planet, including the Earth, underwent at least one collision with another planet. In the Earth's case, scientists believe it collided with a Mars-sized planet around 4.4 billion years ago. The collision had the potential of completely destroying both planets, yet it happened at just the right angle that Earth was able to absorb most of the collision. It resulted in a massive amount of debris being ejected into orbit. Eventually, that debris coalesced to form Earth's moon.
The Origin Of Life
The origin of life is one of the most significant moments in the history of planet Earth. Exactly how or when life began on Earth remains a mystery. The earliest concrete evidence of biological organisms dates to around 3.7 billion years ago, yet some lines of evidence suggest life could have formed as early as 4 billion years ago. Unfortunately, not a lot of rocks are left from these early eras of Earth's history, so piecing together the origin and history of life is a tremendously difficult task. As of yet, how life formed, where it formed, and when it formed are among modern science's most pressing questions. However, one thing that can be said is that the formation of life forever changed our world. Everything from the chemistry of our atmosphere to the geology of Earth's surface has been impacted by living things. The Earth would not be the planet it is today without the existence of life.