Have you ever wondered what life on Earth was like before humans existed? Or have you ever imagined what the planet looked like in its earliest days, when it was still a hot, molten ball of rock? Well, scientists may not have invented a time machine yet, but they have been able to piece together the history of our planet using various methods and evidence.

Let’s take a quick journey through the past 4 billion years of Earth’s history.

4 billion 600 million years ago: Our planet didn’t exist yet. There was only a newly formed proto-Sun and a ring of gas and dust.

4 billion 540 million years ago: Earth was formed. The conditions on the planet were harsh and inhospitable, with a surface temperature reaching 4,700 degrees Celsius (8500 degrees Fahrenheit) and an atmosphere consisting of carbon dioxide, nitrogen, sulfur, and water vapor. The planet was also bombarded by large asteroids.

4 billion 100 million years ago to 3 billion 800 million years ago: The late heavy bombardment occurred, with a large number of asteroids hitting the Earth. Scientists theorize that there may have been oceans on the planet at this time, despite its high temperature.

3 billion 800 million years ago: The temperature of Earth began to slowly decline, but there was still no oxygen in the atmosphere and no ozone layer to block ultraviolet radiation. However, there are fossils dating back to 3 billion 500 million years ago, suggesting that life on Earth may have arisen much earlier than previously thought.

3 billion 200 million years to 2 billion 800 million years ago: The Earth’s surface was mostly covered by a shallow ocean with a temperature ranging from 55 to 88 degrees Celsius (131 to 190 degrees Fahrenheit). Microorganisms inhabited this hot water, and the land consisted of volcanic islands.

2 billion 500 million years ago: The first supercontinent, Kennerland, formed.

1 billion 500 million years ago: Earth’s days lasted at least 16 hours, but complex organisms still didn’t exist. Lithospheric plates continued to move, eventually creating the supercontinents Rodinia and Pangaea.

650 million years ago: The “snowball Earth” theory suggests that the planet was completely covered in ice, with even the Equator as cold as modern Antarctica.

550 million years ago: The Cambrian explosion occurred, with a sudden proliferation of diverse life forms.

230 million years ago: Pangaea began to break apart, leading to the formation of the continents as we know them today.

65 million years ago: The dinosaurs went extinct, possibly due to a meteor impact.

2 million years ago: Homo sapiens (modern humans) evolved.

And that brings us to the present day! While the history of Earth may seem daunting, it’s important to remember that it all happened over the course of billions of years. Understanding the past helps us to better understand the present and prepare for the future.

Artist’s impression of the Hadean Eon. Credit: Tim Bertelink, CC BY-SA 4.0