10 Catastrophic Events that Transformed the Earth

Our world is a fragile place. Even what might appear to be nothing more than a minor change to the global climate can have the effect of irrevocably transforming the ecosystem. Just the slightest alteration in any of the specifications that define our world, such as its axial tilt or the average global surface temperature, can change the course of evolution. On one hand, life as a whole has proven incredibly resilient, having fought for survival for at least 3.5 billion years. On the other, countless catastrophic events transformed the Earth before, profoundly altering the course of evolution and leaving a trail of destruction in their wake. In this week’s listicle, we will look at 10 of the most important of these turning points in the history of our world.

#1. Formation of the Moon – 4.5 bya (billion years ago)

An artist’s impression of two planet-sized objects colliding, like the event that formed the Moon.

It’s easy to think of the Moon as nothing more than a dead and dusty world. However, as I explained in last week’s listicle, we would be pretty much doomed without it. Although no one knows for sure, the most commonly excepted explanation of the Moon’s formation is the giant impact hypothesis. The hypothesis claims that, some 4.5 billion years ago, there was a catastrophic impact event between the young Earth and another planet-sized object. Precariously sharing the same orbits, these bodies hurtled into one another, with the smaller one breaking up entirely to form a ring around the world. Eventually, compelled by the forces of gravity, the countless rocky remnants came together to form our Moon.

#2. Lunar Cataclysm – 4.1 to 3.8 bya

Hadean EarthNASA

The early Earth was under constant bombardment from asteroids and comets.

The young solar system was a volatile place where the planets formed from a proto-planetary disk. Countless impact events and collisions both destroyed and created new worlds. The latter part of this event is known as the Lunar Cataclysm or the Late Heavy Bombardment. During this time, many of the left-over remnants from the formation of the inner planets collided with the Earth and its young moon. The event is postulated to have lasted some 300 million years, when the environment of the early Earth was chaotic to say the least. Fortunately, no life is believed to have existed at this time. However, it may have been that such an impact event ultimately seeded our world with the chemistry for life.

#3. Plate Tectonics – 4 bya to present

Tectonic rift in IcelandPixabay

The rift between the North American and Eurasian tectonic plates runs right through the heart of Iceland.

The early Earth was a truly inhospitable world, with most theories postulating that it was extremely hot and possibly even covered with a global ocean of magma. The first atmosphere would have consisted primarily of hydrogen and helium left over from the planet’s formation. However, as the liquid crust started to cool, the evolution of plate tectonics took place. This event was instrumental in making the Earth habitable, since it gave rise to the formation of the first continents. However, equally important is that fact that volcanism, caused by tectonic activity, also helped to give our world a life-bearing atmosphere as well as the oceans. The evolution of plate tectonics has proven critical for jump-starting the chemistry of life.

#4. Oxygen Holocaust – 2.5 to 2.3 bya

CyanobacteriaJosef reischig

Cyanobacteria was the caused of a major extinction event in the early Earth.

Among the first life on Earth was cyanobacteria, the same phylum that forms that algae-like green scum on the surface of stagnant bodies of water. The reason it’s green is because it’s photosynthetic, meaning that it obtains its energy from the Sun, producing oxygen as a by-product. As we all know, oxygen is crucial to almost all life on Earth, both maritime and terrestrial. However, anaerobic organisms, such as many of those that reside in our own bodies, cannot survive in environments that contain free oxygen. Eventually, cyanobacteria started producing more oxygen than the environment could handle, thus bringing about the first greatest extinction event in Earth’s history – the Great Oxygenation Event.

#5. Mass Glaciations – 850 to 635 mya (million years ago)

Antarctic glaciers and icebergsPixabay

Long ago, the whole world would have looked much like Antarctica.

During a geological period known as the Cryogenian in the Proterozoic Aeon, the Earth is believed to have almost completely frozen over. The Snowball Earth hypothesis draws evidence from the discovery of glacial deposits from regions that were, in the extremely distant past, once tropical. Unsurprisingly, these mass glaciations changed the course of evolution. Evidence even goes so far as to suggest that the coastal erosion that accompanied the event deposited a great deal of phosphorous into the ocean, a crucial element for all life on Earth. However, the hypothesis remains controversial, and while it is clear that major glaciations did indeed occur, their extent remains largely unknown.

#6. Cambrian Global Warming – 541 to 485.4 mya


Anomalocaris, the iconic super-predator of the Cambrian Period.

Human-caused global warming is the concern of the century, but even our impact on the environment is minimal compared to that of nature itself. The global climate has changed countless times through the course of our planet’s history, to the extent that palm trees once grew in Antarctica. One of the main causes of global warming is an increase of atmospheric CO2, a by-product of life itself. In few periods throughout Earth’s history was global warming as profoundly influential as it was during the Cambrian Period. CO2 levels skyrocketed to over 11 times their current level, and average surface temperatures reached 7 °C. These conditions ultimately lead to the Cambrian Explosion, which saw the evolution of most modern phyla.

#7. Oceanic Anoxia – 375 to 360 mya

Ocean wavesPixaba

Oxygen-poor oceans are bad environments for most forms of maritime life.

The Late Devonian extinction was one of the major extinction events in the Earth’s history. Around a half of all the planet’s genera died out, but marine ecosystems were left utterly devastated. Many iconic species of the time, such as the massive armoured fish dunkleosteus, died out, choking to death in oxygen-poor waters. Coral reefs all over the world were largely destroyed, and the many animals that relied on them soon followed as oxygen levels in the oceans plummeted in what is known as an anoxic event. However, terrestrial life was thriving as the very first amphibians evolved from fish, exploring the land to escape the dying waters.

#8. Great Dying – 252 mya

Remains of a dimetrodon, which died out in the PermianH. Zell

Dimetrodons were among the many species killed off by the Permian-Triassic extinction event.

Of all the mass extinctions that have devastated our world throughout its history, none were quite so profound as the Permian-Triassic event. Marine ecosystems suffered the heaviest blow of all, with 96% of species vanishing forever, including the last of the trilobites. In fact, the event was so disastrous that it took at least 10 million years for biological diversity to reach its pre-extinction levels. The extinctions also led to a coal gap, meaning that no coal deposits were formed in the Early Triassic that followed. There simply wasn’t enough organic matter left on Earth to form them! Also known as the Great Dying, the Permian extinctions put the brakes on evolution, thus profoundly changing its course.

#9. Chicxulub Impact Event

An asteroid impact is by far the most probably cause of the dinosaurs’ demise.

Easily the best known of all the catastrophic events that changed the Earth was that which wiped out the non-avian dinosaurs. The Cretaceous-Paleogene extinction event saw the demise of almost every tetrapod species weighing more than 55 lb (25 kg), with the exception of sea turtles and crocodiles. The most widely accepted cause is the Chicxulub impactor, a 6-mile-wide (10 km) asteroid or comet that hurtled into the ocean in what is now the Gulf of Mexico. The resulting megatsumami caused mass destruction on a truly unimaginable scale, and the following impact winter brought life on Earth to its knees. However, the demise of the dinosaurs also meant that mammals had a new niche in which to evolve and thrive, eventually leading to…

#10. The Arrival of Humans

Artist's impression of global warmingPixabay

Sadly, humans can be credited with the overwhelming majority of recent and extinctions and endangered species.

The arrival of humans, the distant descendants of the mammals that thrived following the Cretaceous mass extinction, has and continues to transform the world. As the only fully sentient species to ever live on Earth, humans have also been the cause, either indirectly or directly, of countless extinctions. We are now living in the midst of what many scientists describe as the Holocene Extinction Event. Industrialisation has led to major artificial changes to our climate, including a 50% increase in atmospheric CO2 levels. However, it’s not just manmade global warming that is continuing to change the course of evolution; human encroachment on natural habitats over the last 12,000 years has had the greatest influence of all.

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