Over 4.5 billion years, volcanoes, asteroids, and climate change have wiped out millions of species.
While life on Earth does usually find a way, it is not without some intense past–and future–periods of mass death. Extinction is not exclusive to dinosaurs. Our planet has gone through at least five periods of mass extinction, with the planet likely in a sixth wave of mass extinction–this one, driven by humans. Ordovician-Silurian extinction: An Appalachian connection The formation of the Appalachian Mountains may have triggered massive global cooling. CREDIT: Deposit Photos. Our planet's first known mass extinction happened about 440 million years ago. Species diversity on Earth had been increasing over a period of roughly 30 million years, but that would come to a halt as water began to freeze in a massive ice cap towards the south pole. The formation of the Appalachian Mountains was the potential cause of this cooling. When the supercontinent Gondwanaland collided with what is now North America, the ancient lapetus Ocean closed over a period of about 150 million years. The weathering of the freshly uplifted rocks from this continental collision may have sucked carbon dioxide out of the atmosphere. As a result, the planet drastically cooled, sea levels plummeted, and roughly 85 percent of species were wiped out. Due to this drop in sea levels, it was particularly hard on marine species including brachiopods, corals, and trilobites. The Devonian extinctions: Pulses of death A model of a "Coelacanth fish" is displayed at an exhibition hall on November 4, 2010 in Dresden, Germany. CREDIT: Robert Michael/AFP via Getty Images. Earth's marine species, especially those at the tropics, were in trouble again about 419 million to 365 million years ago. This series of mass extinctions during the Devonian period eventually eliminated about 75 percent of life. However, some of Earth's oldest fish called coelacanths make it out unscathed. Get the Popular Science newsletter Breakthroughs, discoveries, and DIY tips sent every weekday. Email address Sign up Thank you!…