An expert described a grim scenario if Earth never collided with a Mars-sized object billions of years ago. If this cataclysmic event never happened, humans would most likely not exist on the planet.
Many scientists believe that 4.5 billion years ago, Earth collided with an ancient planet known as Theia, which is believed to be as big as Mars. The violent collision caused massive changes on Earth as well as its surroundings.
Earth's Collision With Theia
Due to the magnitude of the impact, a large portion of the Earth's crust melted while some of it was blown off into space. Over time, the chunks of debris that drifted outside Earth coalesced into a solid cosmic body. Eventually, this newly formed object became Earth's Moon.
As various scientific reports have explained, both the Moon and the Sun have had significant effects on the evolution of the planet. For one, the gravitational pull from these cosmic objects is responsible for maintaining the tides of Earth's oceans. This means that if not for the giant impact caused by Theia, Earth would have been very different.
Earth In Non-Impact Scenario
In the question-and-answer site Quora, retired engineer Duncan Caincross attempted to explain what Earth would be like if it didn't collide with Theia. According to Caincross, the cataclysmic event that happened billions of years ago could be responsible for the evolution of complex life on the planet.
He explained that if the impact event did not happen, Earth would be very different and would most likely look like Jupiter's moon Europa, an ocean-filled world with an icy crust. Similar to the conditions on Europa, a pre-impact Earth would most likely not have the necessary elements to support the evolution of complex life.
"Without that impact, the Earth could have been like Europa - with a lot of water," Caincross stated. "A planet with an Ocean that is kilometers deep at the shallowest parts. "That has major repercussions for the development of life - there would be no minerals in the top layers of the ocean - and no sunlight in the lower levels. With such a planet there would be almost no life - the only life would be a tiny amount of life around the volcanic vents."