5 Events That Completely Changed The Earth

Earth has never stood still. Over its 4.5 billion years of history, our planet has been reshaped by different cataclysms and climate shifts. The atmosphere went through several changes, oceans froze solid, and continents collided to form mountain ranges. While some changes were instant, such as the impact of an asteroid (different from the thousands of meteorites that do hit Earth annually), others took time to alter the course of evolution and rewrite the story of Earth. Even the birth of our moon has drastically altered Earth's destiny, and without it, life may not have emerged.

Humans have also become part of this narrative. We are, in many ways, responsible for changing our planet. From the first seeds we sowed during the Agricultural Revolution to the smokestacks of the Industrial Age, our species has transformed whole landscapes, climates, and ecosystems. So let's explore the pivotal events that reshaped Earth in more detail. They reveal that our planet is not a static blue marble in the universe, but rather a dynamic, ever-changing system where history is written in rock, ice, and atmosphere.

About 4.5 billion years ago, when Earth was just an infant planet, the solar system was anything but stable. Planets, proto-planets, and other celestial objects frequently collided, shaping the worlds we know today. One of the most dramatic collisions involved Theia, a Mars-sized celestial body that slammed into our young Earth. The impact was so violent that parts of the new Earth were instantly vaporized. Molten debris was blasted into the orbit of our planet. This orbit wreckage started cooling quickly, and the fragments clumped together, pulled by the gravitational forces.

Once solidified, this new object became Earth's faithful companion, which we now call the moon. We can find evidence of this event in the moon's composition, as it closely mirrors Earth's outer layers. This collision also explains the angular momentum of the Earth-moon system. That said, the impact with Theia did more than just give us the moon. The gravitational pull of the moon stabilized Earth's tilt. As a result, the climate became stable and familiarly moderate, which made the conditions on our planet favorable for life. What began as destruction ended up becoming creation. From a catastrophe, our moon emerged as a stabilizing force in Earth's history, and it may be the reason we're all here today.

One of the most profound transformations of Earth happened approximately 2.4 billion years ago. Before this time, the atmosphere was devoid of oxygen; instead, it was dominated by gases such as methane and carbon dioxide. Even though complex lifeforms might have existed on Earth longer than we initially thought, life at that time was limited to simple, anaerobic microbes. The shift toward greater complexity started with the emergence of cyanobacteria, a microorganism that started releasing oxygen through the process of photosynthesis. What followed is known as the Great Oxidation Event.

The newly introduced oxygen in Earth's atmosphere first started reacting with dissolved iron in the early oceans, potentially turning the green seas of the time into the blue ones we know today. That's actually how the vast deposits of banded iron ore that are still mined today came to be. But eventually, there was so much oxygen that it started accumulating in the atmosphere. Many anaerobic microbes died because oxygen was toxic to them, but for others, it opened the door to new metabolic pathways, including respiration. Over millions of years, oxygen fueled evolution, and the first complex, multicellular life forms came to be.

The Great Oxidation Event permanently altered the chemical composition of Earth's atmosphere, and it even changed Earth's very climate. But that wasn't the end, either. Oxygen in the atmosphere started reacting with methane, resulting in carbon dioxide, which cooled the Earth and started the earliest Ice Age.

About 540 million years ago, life on Earth underwent a dramatic change known as the Cambrian Explosion. Before this event, life on our planet was very simple. It consisted of single-cell organisms such as microbes, algae, and a few soft-bodied multicellular forms. Then, in a relatively short geological timespan of about 20 million years, the diversity of life on Earth exploded.

Fossil evidence from various sites reveals the sudden emergence of nearly all major animal groups during this time. This is the period when arthropods, mollusks, and early ancestors of vertebrates evolved. Hard body parts such as exoskeletons and shells came to be, as they improved the survival of many species and conveniently left behind a rich fossil record. Predation became widespread, sparking evolutionary races among different species. Suddenly, both prey and predators had to evolve new, useful body parts that would ensure their survival.

However, scientists still debate what sparked the Cambrian Explosion. It could be the sudden rise of oxygen levels, the development of hox genes (bits of genetic code that help organize a creature's body), or an end to the massive glaciers that ruled the seas. It could also be a combination of these events, but it's certain that the Cambrian Explosion reshaped the tree of life.

The Permian-Triassic Extinction was the most catastrophic of the numerous mass extinction that have happened on Earth. No wonder it's also known as the Great Dying. It happened around 252 million years ago, but it wasn't a sudden event such as an asteroid impact or a volcanic explosion. The Great Dying unfolded over hundreds of thousands of years, during which more than 90% of Earth's life was wiped out.

Scientists still debate the exact causes, but the massive volcanic activity in today's Siberia is the leading suspect. These eruptions released staggering amounts of carbon dioxide and methane into the Earth's atmosphere, triggering drastic global climate changes. The oceans acidified. The oxygen levels in the water collapsed. The marine life suffocated over time. And the situation on land wasn't much different. The soaring temperatures devastated both plant and animal life.

The Great Dying reset the evolutionary clock. The ecosystem was left sparse and unstable, but it's from this devastation that new opportunities for life developed. In the aftermath of this extinction event, surviving species spread and evolved. This is the period when early reptiles came to be, setting the stage for the development of dinosaurs and early mammals. Once again, life emerged from the ashes.

Natural forces shaped the Earth for billions of years, but in modern times, it's humanity that has emerged as an Earth-changing force in its own right. The first transformation of our planet caused by humans came with the Agricultural Revolution, around 12,000 years ago. By domesticating plants and animals, humans altered whole landscapes and began reshaping the ecosystems around them to sustain their growing populations. Settlements, irrigation systems, and cultivation set the stage for the first civilizations, but also for long-term environmental change.

The Industrial Revolution of the 18th and 19th centuries only accelerated this impact. Powered by coal, steam, and oil, it unleashed the energy that would be the driving force behind urbanization and technological progress. However, it also started the large-scale release of greenhouse gases, initiating drastic climate shifts that we still deal with to this day. Earth's atmosphere, once shaped by biology and geology, became increasingly influenced by human activity.

Then along came the Nuclear Age of the 20th century, which added a new signature to Earth's long record. Atomic bomb tests and nuclear research scattered radioactive isotopes worldwide, creating a permanent geological marker detectable in soil and sediment, influencing our environment and the very fragile life on Earth. How we will continue to influence the evolution of our planet remains to be seen.