More than 400 million years ago, Earth's dramatically warmer sea temperatures plummeted to almost present-day levels, opening the door for a boom in biodiversity, new research shows.
The cooler seas—which occurred during the Ordovician period—created a more hospitable environment for a range of species, researchers say.
The find might also foreshadow a biodiversity crisis if the planet continues to warm due to climate change.
"It's a warning of what happens to life on Earth when global temperatures get extremely high," said study co-author Chris Barnes, a paleontologist at the University of Victoria in British Columbia, Canada.
"Life can exist, but it is not as diverse."
Biodiversity Boom
Sea-surface temperatures hovered at about 108 degrees Fahrenheit (42 degrees Celsius) near the beginning of the Ordovician, 490 million years ago, researchers found.
The temperature fell dramatically to modern-day tropical climes by 470 million years ago, then cooled further during a brief glacial period to about 73 degrees Fahrenheit (23 degrees Celsius) around 443 million years ago. As oceans cooled to modern levels, life bloomed. At the beginning of the period, the sea averaged about 350 to 400 species, but those numbers soon spiked to more than 1,700, Barnes explained.
(Read about ancient horseshoe crab fossils found from the Ordovician period.)
"What we can show in this [research] is that this sudden expansion in the evolution of life occurred only over about five to ten million years. Thats really quite astonishing," Barnes said.
New Technique
Traditionally scientists have used oxygen isotopes—versions of an element with different masses—to measure ancient ocean temperatures. That's because ratios of these isotopes change based on sea temperatures.
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