Meandering rivers shaped early landscapes before plants arrived

When we picture Earth’s ancient landscapes, it’s easy to imagine vast braided rivers sprawling across barren land. For decades, geologists believed this was the norm until plant life colonized land about half a billion years ago.

Vegetation, experts argued, gave rivers the stability needed to curve gracefully into meandering paths. A new study from Stanford University now turns this long-held assumption on its head.

Origins of meandering rivers

The research shows that unvegetated meandering rivers can leave behind deposits that closely resemble those of braided rivers. This finding suggests that geologists may have misread the rock record, leading to the conclusion that braided rivers dominated most of Earth’s first 4 billion years.

“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 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.”

The role of floodplains

Meandering rivers create floodplains, which are among the most abundant non-marine carbon stores on the planet. Overflows deposit mud and organic matter, locking carbon into the land for thousands of years.

These natural reservoirs influence atmospheric carbon dioxide, Earth’s thermostat. A better grasp of their history could refine models of climate, both ancient and future.

“Floodplains play an important role in determining how, when, and whether carbon is buried or released back into the atmosphere,” Hasson said.

“Based on this work, we argue carbon storage in floodplains would have been common for much longer than the classic paradigm that assumes meandering rivers only occurred over the last several hundred million years.”

Tracking modern rivers

To test their idea, the team analyzed satellite imagery of about 4,500 bends in 49 present-day meandering rivers. Roughly half lacked vegetation, while the rest were vegetated to varying degrees.

The researchers focused on point bars, sandy features that form along inside bends. Unlike braided rivers’ mid-channel bars, point bars migrate laterally, driving meandering forms over time.

Geologists have long tracked these sandy structures in ancient rocks to reconstruct river paths. If the bars seemed to shift downstream, the conclusion was a braided system. This method led to the assumption that rivers transformed when plants first evolved.

Old geology lessons were mistaken

“In our paper, we show that this conclusion – which is taught in all geology curricula to this day – is most likely incorrect,” said study senior author Mathieu Lapôtre, assistant professor at the Doerr School of Sustainability.

The team found that without vegetation, point bars often drift downstream, mimicking braided behavior. Using standard geological techniques on such rivers today would misclassify them as braided.

“In other words, we show that, if one were to use the same criterion geologists use in ancient rocks on modern rivers, meandering rivers would be miscategorized as braided rivers,” Lapôtre said.

Meandering rivers shaped climate

The implications are sweeping. If meandering rivers, with their carbon-rich floodplains, existed long before plants, then Earth’s carbon cycle operated differently than once thought.

This insight could reshape models of ancient climate shifts and sharpen predictions about current climate change.

“Understanding how our planet is going to respond to human-induced climate change hinges on having an accurate baseline for how it has responded to past perturbations,” Hasson said. “The rock record provides that baseline, but it’s only useful if we interpret it accurately.”

Revising Earth’s story

The study suggests that carbon cycling tied to river style has been misunderstood. By correcting this, scientists can gain clearer insight into both the deep past and the uncertain future.

“We’re suggesting that an important control on carbon cycling – where carbon is stored, and for how long, due to river type and floodplain creation – hasn’t been fully understood,” Hasson said. “Our study now points the way to better assessments.”

Researchers from the University of Padova and the University of British Columbia also contributed to the study.

The study is published in the journal Science.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–