Summary
Highlights
Life on Earth has faced five major mass extinction events, with 98.5% of all organisms that ever lived now extinct. Each event devastated existing life forms, but also paved the way for new evolutionary bursts and the rise of different dominant species. The current diversity of life is a result of these cycles of annihilation and renewal, with survivors adapting to fill newly empty ecological niches.
Around 450 million years ago, Earth experienced its first great dying during the Ordovician period. Warmer temperatures initially led to vast oceans and thriving marine life, including trilobites, corals, and early fish. However, a sudden 4-degree drop in ocean temperature triggered a brutal ice age, causing sea levels to fall and vital habitats to shrink. This climate shift, followed by a subsequent warming, led to the extinction of 85% of species, but hardy bony fish survivors laid the groundwork for all future vertebrates, including humans.
Millions of years after the Ordovician extinction, the Devonian period saw a new era of life. The oceans were dominated by creatures like the formidable Dunkleosteus, a super-predator of the age of fish. Simultaneously, continents transformed from barren land to vast forests, with trees releasing water vapor that may have intensified storms. Runoff from these storms choked oceans, causing oxygen levels to plummet. This second mass extinction led to the collapse of marine food chains, extinguishing three-quarters of marine life. However, certain fish, like Tiktaalik, with their lobe-like fins and primitive lungs, began to venture onto land, marking a pivotal moment in the evolution of amphibians.
The Permian period saw the development of modern trees, enriched oxygen levels, and the formation of the supercontinent Pangaea. Land animals evolved, with creatures like the sail-backed Dimetrodon and the armored Daedobeasts, hunted by predators like Titanon. The seas also diversified with unique sharks like Helicoprion. However, this spectacular biodiversity was obliterated approximately 250 million years ago by the Permian-Triassic extinction, the most devastating natural catastrophe Earth has seen. Massive volcanic eruptions in Siberia, forming the Siberian Traps, released greenhouse gases and sulfur oxides, causing extreme acid rain, global temperature shifts, and a collapse of ecosystems. This event wiped out 96% of marine species and a significant portion of land life. Small, adaptable creatures like ostracods survived by reducing their metabolism and reproductive cycles.
Following the Permian devastation, life once again reset during the Triassic period. Surviving tetrapods evolved into reptiles, dinosaurs, and early mammals. Marine reptiles like Ichthyosaurs, corals, and ammonites flourished in the oceans, while Pterosaurs took to the skies. On land, armored herbivores and agile predators like Coelophysis, one of the first dinosaurs, emerged. The Earth entered another period of volcanic upheaval around 200 million years ago, causing the fourth mass extinction, which wiped out three-quarters of land-dwelling species and 96% of ocean species. However, some lineages of dinosaurs, mammals, and pterosaurs survived, setting the stage for the age of giants.
The High Jurassic and Cretaceous periods saw the dominance of mega-dinosaurs. After the Triassic extinction, dinosaurs rapidly grew to enormous sizes, with species like Ledumahadi, a 12-ton sauropodomorph that walked on all fours, and massive sauropods reaching 100 feet long. Evolution reached extremes with creatures like the T-Rex, huge pterosaurs, and marine predators like Plesiosaurus and Mosasaur. Dinosaurs ruled for over 175 million years, until approximately 66 million years ago. While volcanic activity in India (Deccan Traps) contributed, the fifth and most famous mass extinction was triggered by an extraterrestrial asteroid impact in the Yucatan Peninsula. This impact caused instant devastation – blinding light, intense heat, massive earthquakes, tsunamis, and global wildfires, plunging the planet into darkness and causing widespread ecological collapse. All large dinosaurs were wiped out, along with three-quarters of all species.
After the fifth mass extinction, Earth belonged to the small survivors. Tiny, shrew-like mammals, previously living in the shadow of dinosaurs, rapidly diversified and grew in size. Within 15-20 million years, they evolved from small rabbit-sized creatures to large hippopotamus-sized pantodonts, and later to elephant and rhinoceros-sized animals. These great extinction events were revolutions, allowing new branches on the tree of life to bloom and fill the void. This led to the sixth Earthly paradise, dominated by diverse mammals, including primates. However, the current mass extinction is unique; it is 100% human-caused, happening at an unprecedented rate, and considered by many to be a mass suicide. While life will undoubtedly regenerate, the future actors on the planetary stage remain unknown, emphasizing the fragility of Earth's complex web of life.