The Amazon rainforest survived a climate that should have destroyed it

Nature · Published 23 October 2026 Swipe more like this →

In short: For millions of years, the Amazon has faced extreme climate shifts, from glacial periods to dramatic shifts in water flow. While some scientists believe the forest nearly vanished into isolated pockets of greenery, others argue it held its ground. This resilience is what allowed it to become the world's most biodiverse tropical tract.

The Amazon's existence is a story of geological and climatic endurance. It likely formed during the Eocene era, roughly 55 million years ago, following a global drop in tropical temperatures and the widening of the Atlantic Ocean. This created the warm, moist climate necessary for a broadleaf forest to take hold. During the Cretaceous–Paleogene extinction event, the disappearance of dinosaurs and a shift toward wetter climates may have even allowed the rainforest to spread across the continent as far south as 45° latitude.

The geography of the basin was not always what it is today. During the mid-Eocene, the Purus Arch split the drainage basin; water flowed toward the Pacific on one side and the Atlantic on the other. It wasn't until the last 5 to 10 million years that the rising Andes Mountains and the accumulation of water in the Solimões Basin forced the water to break through the Purus Arch, joining the flow toward the Atlantic.

The greatest mystery lies in the Last Glacial Maximum (LGM). Evidence from sediment deposits suggests rainfall was lower then, leading to a debate among researchers. Certain researchers propose that grasslands divided the rainforest into tiny, disconnected pockets of survival. Conversely, another group argues the forest remained largely intact but with a smaller geographic footprint. Since data collection avoids the basin's core, these two perspectives persist, showcasing how the woodland endured despite extreme environmental pressure.

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

• The Amazon holds one in ten of Earth's known species
• The Amazon pumps 7 trillion tons of water into the atmosphere annually
• The Amazon rainforest exists because of a massive river flowing through the sky
• Andean uplift helped shape the immense biodiversity of the Amazonian rainforest
• The Amazon basin was once a westward-flowing river system before the Andes mountains formed.
• Navigating the world’s largest and most dangerous jungle
• Survival and adaptation in Borneo's 100-million-year-old rainforest
• The hidden architecture beneath the Amazon's forest floor
• The Amazon's inhabitants: A 4K journey through the jungle's biodiversity
• A Five Metre Anaconda Leads Researchers to a Surprising Discovery in Guyana
• The Amazon Basin hides ancient cities beneath its dense canopy
• Many venomous snakebites carry no venom at all, by the snake's choice

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