Ancient Rivers Meandered Long Before Plants Evolved, Stanford Scientists Find

For many years, scientists believed that rivers began to meander i.e., they started to twist and turn in S-shaped patterns after plants appeared on land. However, a recent study challenges these long-held beliefs among geologists. Previously, experts believed that before plants evolved, rivers mainly flowed in straight paths breaking into multiple channels and moving around sandbars. The idea was that once plants grew and helped hold soil in place, slowing erosion, rivers began to take on the smooth, winding curves that are seen today.

This new research was conducted by scientists at the Stanford University and published on August 21, 2025, in the journal Science. According to experts, rivers may have started meandering long before plants even existed, and earlier geologists might have misinterpreted the rock evidence from millions and millions of years ago. The layers of rock are examined to understand what rivers looked like during that period. Different types of rivers leave behind different patterns in the rock, especially in sandstone and mudstone.

In braided rivers, sandy bars form in the middle of the river and move downstream. In meandering rivers, sandy features called point bars form on the inside of each bend. These bars gradually shift sideways over time, contributing to the river's winding path.

New Findings

Traditionally, the direction of these sandy bar movements in ancient rocks are used to determine the type of river that created them. If the bars moved downstream, they were assumed to belong to braided rivers. If they moved sideways, the river was thought to be meandering. Since many ancient rocks have downstream-moving bars, it was believed that early Earth had mainly straight, braided rivers, until plants evolved and changed the river shapes.

To conduct the research, the scientists examined satellite images of 49 meandering rivers around the world. Some of these rivers flowed through areas with lots of vegetation, while others ran through barren, plant-free regions like deserts. Their findings were surprising: even rivers without plants could meander.

This means that if scientists only looked at the direction those bars moved, as they do with ancient rocks, they would mistakenly assume these meandering rivers were braided. Therefore, the method scientists have long used may be flawed.

What Does It Mean for the Climate?

If meandering rivers existed long before plants, then carbon-rich floodplains may have formed much earlier on Earth than previously thought. These floodplains are important as they act as carbon storage units. They trap carbon that would otherwise be released into the atmosphere as carbon dioxide. Since carbon dioxide influences Earth's temperature, knowing when and where it was stored helps scientists understand how Earth's climate has changed over time.

"With our study, we're pushing back on the widely accepted story of what landscapes looked like when plant life first evolved on land," said lead author Michael Hasson, a PhD student in Mathieu Lapôtre's lab at the Stanford Doerr School of Sustainability. "We're rewriting the story of the intertwined relationship between plants and rivers, which is a significant revision to our understanding of the history of the Earth."

By understanding how Earth's climate changed in the past is crucial for predicting what might happen in the future. It can help scientists find ways to study how Earth evolved over billions of years and what we can do to protect our future.

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