Life on Earth has always had a flair for the dramatic. Over billions of years, our planet has hosted cataclysmic extinction events that wiped out species en masse, only for new life forms to evolve. In this blog, we’ll explore humanity’s unique ability to both create and destroy, alongside the fascinating history of the Big Five mass extinctions and other significant extinction events.
Humanity: Masters of Creation and Destruction
Life and death, creation and destruction—two sides of the same coin. While humanity’s boundless creativity has catapulted us to the top of the food chain, we’ve wreaked havoc on nature along the way. From deforestation to overfishing, our innovations have often come at a steep cost to biodiversity. The things we’ve created—plastics, skyscrapers, artificial lifestyles—don’t break down easily (if at all).
Our impact is undeniable: human activity is driving extinction rates 100 to 1,000 times faster than the natural background rate. But before we get too carried away with guilt, let’s rewind to examine extinction events of the past, where nature itself has been the architect of mass destruction.
What Are Background Extinction Rates?
Background extinction rates refer to the natural pace at which species go extinct over time, independent of major catastrophic events. These rates are a baseline measurement of biodiversity turnover, reflecting the gradual disappearance of species due to environmental changes, competition, or evolutionary shifts. Typically, one to five species per year might vanish under natural conditions. However, current extinction rates far exceed this norm, underscoring the impact of human activity on the planet’s ecosystems.
What Are Mass Extinctions?
Mass extinctions occur when environmental changes happen so rapidly that species can’t adapt in time. Whether it’s volcanic eruptions, asteroid impacts, or a sudden ice age, these events disrupt ecosystems on a global scale, leading to widespread extinction. Yet, paradoxically, they’ve also paved the way for new species to evolve. Without these extinction events, humans might never have had a chance to dominate the planet.
A Timeline of Earth’s Biggest Extinction Events
The history of life on Earth is punctuated by five particularly massive extinction events, often called the “Big Five.” These dramatic moments reshaped life on our planet, but they’re not the whole story. Other events, while smaller in scale, have also played a crucial role in shaping evolution. Let’s explore these extinction milestones:
The Great Oxidation Event (2.4 billion years ago)
The Great Oxidation Event was driven by the evolutionary leap of cyanobacteria, the first organisms capable of photosynthesis. These microbes released oxygen as a by-product, gradually saturating the atmosphere. While this influx of oxygen was toxic to anaerobic organisms that thrived in oxygen-free environments, it set the stage for the development of more complex, aerobic life forms. This event also led to the formation of the ozone layer, which protected emerging life from harmful ultraviolet radiation and ultimately paved the way for multicellular organisms to flourish. This “pollution” led to Earth’s first extinction event but also set the stage for complex life to evolve.
End-Ediacaran Extinction (550 million years ago)
The End-Ediacaran extinction marked the decline of many soft-bodied organisms which thrived in the nutrient-rich, predator-free oceans of the Ediacaran period. However, the Cambrian explosion ushered in a new era of evolution, with the rise of predators like arthropod-like creatures that fundamentally altered marine ecosystems. Hard shells, spines, and burrowing behaviours emerged as critical survival adaptations, reshaping the dynamics of ocean life and paving the way for the Cambrian period's more diverse and complex ecosystems. Enter hard shells and new behaviours like burrowing, which transformed life on Earth.
Ordovician Event (444 million years ago)
The Ordovician event is the first of the Big Five events and began with a dramatic glaciation. This shift caused widespread cooling and ice sheet formation. As ice accumulated, sea levels plummeted, devastating shallow marine habitats that housed most of Earth’s biodiversity. Subsequent melting caused sea levels to rise rapidly, further disrupting ecosystems. This wiped out 85% of marine species. However, in its aftermath, new opportunities emerged, paving the way for plants and insects to begin colonizing land, a crucial step in Earth’s evolutionary history. It was after this that plants and insects began to colonise land.
Late Devonian Extinction (359 million years ago)
A series of extinction pulses over millions of years reduced marine biodiversity by 75%. Land plants may have been the culprits, altering the carbon cycle and oceanic oxygen levels. While the cause of this extinction event isn’t formally confirmed as being the fault of the land plants draining resources from the ocean, other theories include global cooling or oceanic volcanism. This mass extinction caused a huge loss in biodiversity which took a long time to recover.
The Great Dying (252 million years ago)
The Permian extinction—Earth’s most catastrophic—wiped out 96% of species. The event itself lasted less than 500,000 years and had many causes. Greenhouse effect was potent, temperatures rising and dropping. It’s theorised that a super volcano erupted, located in modern day Siberia. Huge quantities of carbon dioxide and methane were pumped into the atmosphere causing temperatures to rise and the oceans to become acidic. Oxygen levels dropped from around 30% to 10%.
For 5 million years after this event, the climate and atmosphere continued to fluctuate dramatically causing more death. During these 5 million years, there was also a coal gap and a coral gap meaning there were no forests of coral reefs. It took a leisurely 100 million years to fully recover.
Triassic-Jurassic Extinction (200 million years ago)
The Triassic-Jurassic extinction event, occurring around 200 million years ago, was primarily driven by volcanic activity linked to the breakup of the supercontinent Pangaea. As Pangaea fragmented, volcanic eruptions released massive amounts of carbon dioxide and other gases into the atmosphere, leading to rapid climate changes, including global warming and a drop in oxygen levels. This environmental upheaval caused the extinction of roughly 70% of terrestrial species, including many reptiles and amphibians. However, it created ecological space for dinosaurs, which had been emerging in the late Triassic. Dinosaurs' highly efficient respiratory systems, which allowed them to process oxygen more effectively, gave them an edge in the oxygen-depleted atmosphere. This adaptation not only allowed dinosaurs to dominate but also influenced the evolutionary path of birds, their descendants, who inherited these advanced breathing mechanisms.
Cretaceous Extinction (66 million years ago)
This event is the last of the Big Five and occurred around 66 million years ago. It was triggered by a massive asteroid impact near what is now the Yucatan Peninsula in Mexico. The impact released an enormous amount of energy, triggering wildfires, tsunamis, and a "nuclear winter" effect. The dust and debris thrown into the atmosphere blocked sunlight, drastically reducing temperatures and disrupting ecosystems. This catastrophic event led to the extinction of approximately 75% of all species on Earth, including the non-avian dinosaurs. With the dinosaurs gone, mammals, previously small and overshadowed, were able to flourish and evolve into the diverse range of species, including humans that would dominate the planet in the following epochs.
While the Big Five are the most well-known, smaller extinction events like the Great Oxidation or the End-Ediacaran also deserve attention for their profound impact on life’s trajectory. Each extinction tells a unique story of upheaval and renewal.
Modern Extinctions: Humanity’s Legacy
Unlike past extinction events, today’s crises are largely man-made. From Australia’s megafauna to the dodo, our actions have systematically wiped out species over millennia. Industrialisation, habitat destruction, and climate change have only accelerated the pace.
A few notable examples:
50,000 years ago: Australia’s megafauna vanished, likely due to human hunting and environmental changes.
1690s: The dodo succumbed to hunting and habitat loss in Mauritius.
19th century: The great auk, a flightless seabird, was driven to extinction by overhunting.
20th century: Passenger pigeons were hunted to extinction in North America, and the Tasmanian tiger fell victim to habitat destruction and bounty hunting.
21st century: Amphibians like the golden toad and Sumatran rhinoceros are also on the brink due to habitat destruction, disease, and poaching.
Today, countless species teeter on the brink. If we’re to break this cycle, we must reconsider our choices—starting with how we consume resources and protect ecosystems.
Lessons from Extinction Events
In the past, extinctions were nature’s way of hitting the reset button. But modern extinction events are a grim reflection of humanity’s unchecked influence. By understanding these patterns, we can strive to be stewards of the Earth rather than its undoing. Small changes—eating less meat, supporting conservation efforts, or investing in sustainable technologies—can have a collective impact.
Further Exploration
Hungry for more? Consider delving into these fascinating topics:
- The Great Oxidation Event and its role in shaping Earth’s atmosphere.
- The enigmatic Ediacaran fauna and their sudden disappearance.
- The role of greenhouse gases in past and present climate shifts.
At Evolution of Stuff, we explore the complex web of history, science, and humanity’s role in shaping our world. Want to keep learning? Sign up for our newsletter, leave a comment, and join the conversation. Together, let’s uncover the stories that make us who we are.
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