The Ordovician period transformed Earth from a simple marine world into a complex ecosystem.

Nature · Published 29 September 2026 Swipe more like this →

In short: Spanning over 43 million years, the Ordovician was a time of radical biological innovation and tectonic upheaval. It hosted the Great Ordovician Biodiversification Event, which set the template for marine life for the rest of the Paleozoic, while simultaneously witnessing the first tentative steps of life onto land.

Defined by Charles Lapworth in 1879, the Ordovician period covers the interval from 486.85 to 443.1 million years ago. It was a time of significant geographic reorganization, as the southern supercontinent Gondwana drifted toward the South Pole. During this era, the world was dominated by shallow, warm seas that encouraged the growth of calcium carbonate-secreting organisms. The period is famous for the Great Ordovician Biodiversification Event, which increased marine faunal genera fourfold and established complex ecological systems that persist to this day.

Life in the Ordovician was not limited to the oceans. While invertebrates like molluscs and arthropods reigned in the water, the period saw the earliest evidence of terrestrialization, including non-vascular plants and fungi. Mycorrhizal symbiosis, evidenced by fossils from Wisconsin dating to approximately 460 million years ago, likely facilitated this colonization. Meanwhile, the oceans saw the rise of the first true vertebrates, with jawless ostracoderms appearing in the Middle Ordovician and jawed vertebrates potentially emerging by the end of the period.

The period ended with the second-largest mass extinction of the 'Big Five,' occurring between 447 and 444 million years ago. This event was primarily driven by the Hirnantian glaciation, which followed a dramatic drop in atmospheric carbon dioxide. As ice sheets expanded over Gondwana, sea levels plummeted, destroying the shallow shelf habitats that supported much of the era's diverse life. This extinction occurred in two distinct pulses, devastating tropical taxa during the initial cooling and later impacting cool-water species during the subsequent warming and sea-level rise.

Despite the catastrophe, the Ordovician remains a cornerstone of geological history. It was a time of intense volcanism and tectonic activity, including the formation of the Appalachian Mountains through the Taconic orogeny. From the massive Millburg/Big Bentonite ash fall to the frequent meteorite impacts of the Ordovician meteor event, the period was marked by extreme environmental shifts that ultimately paved the way for the complex life forms that would dominate the Silurian and beyond.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Earth's first great extinction came as ice, then as suffocating warmth
• The Paleozoic's starting line is a burrow in Newfoundland
• The Phanerozoic, the eon of visible life, got its name from a mistake
• The era when life first conquered the land and oceans
• The lost ocean that once separated the continents and built the supercontinent Pangaea
• Are birds just dinosaurs that never went extinct? The evidence is overwhelming.
• Most orchid flowers twist upside down as they open, and for good reason
• The Orinoco crocodile is South America's largest predator, yet it faces imminent extinction.
• Killer whales are dolphins that hunt like wolf packs
• Bird-hipped dinosaurs mostly chewed plants, not meat
• The deep-sea fish that lives for two centuries and was once called a slimehead.
• Why birds are the ultimate model for understanding the mechanics of life on Earth

More in Organisms · More in Nature · Latest · A–Z · All topics