About 250 million years ago, the Permian-Triassic mass extinction killed over 80% of the planet’s species. In the aftermath, scientists believe that life on Earth was dominated by simple species for up to 10 million years before more complex ecosystems could evolve.

Now this longstanding theory is being challenged by a team of international researchers—including scientists from McGill University and Université du Québec à Montréal.

A fossilized ocean ecosystem

Until now, scientists have long theorized that scorching hot ocean conditions resulting from catastrophic climate change prevented the development of complex life after the mass extinction. This idea is based on geochemical evidence of ocean conditions at the time.

Now, the discovery of fossils dating back 250.8 million years near the Guizhou region of China suggests that complex ecosystems were present on Earth just 1 million years after the Permian-Triassic mass