Ancient Riverbeds May Have Been Meandering All Along
Geologists have long held that Earth’s continents were dominated by braided rivers until land plants evolved roughly 425 million years ago. A study published in Science on 21 August 2025 by Michael Hasson of Stanford University and his colleagues challenges this view, suggesting that unvegetated, meandering rivers can leave behind deposits that resemble those of braided rivers.
The Traditional View of Earth’s Early Landscapes
For decades, the standard geological model suggested that early river systems lacked the bank stability provided by roots. Without vegetation to bind sediment, rivers were thought to have operated as shallow, multi-channel braided networks. The emergence of meandering, single-thread rivers—characterized by sweeping loops—was widely attributed to the stabilizing influence of early land plants. According to the Science paper, this interpretation may stem from a misunderstanding of how sediment is deposited. Researchers analyzed satellite imagery from over 4,400 bends across 49 modern rivers. They found that while vegetation produced a 62 per cent increase in the inferred variance of flow direction, it is not a requirement for a river to form a meander.
How Unvegetated Rivers Create “Braided” Signatures
The core of the issue lies in how geologists interpret rock layers. When researchers examine sandstone and mudstone, they look at the orientation of internal beds to determine how a river once moved. Typically, a broad spread of bar-accretion directions is interpreted as a sign of a meandering channel migrating sideways, while limited variation is seen as a sign of a braided system. Hasson’s team discovered that plant-free meandering rivers move differently than their vegetated counterparts. While plants encourage bends to expand outward, barren banks often cause bends to migrate downstream. This downstream movement can create a sediment pattern that looks similar to the mid-channel bars of a braided river. Consequently, many ancient river deposits may have been misclassified for years.
Did you know? The study does not claim that plants had no impact on rivers. Instead, it suggests that plants changed the way rivers moved—shifting them from downstream translation to lateral expansion—rather than simply “inventing” the curve.
Evidence from Pre-Plant Landscapes
The argument that stable rivers existed before land plants is bolstered by other recent findings. In a 2023 Geophysical Research Letters paper, Jeffery Valenza and his team analyzed 1.2-billion-year-old rocks from the Stoer Group in Scotland. They found evidence of deep, high-sinuosity channels that existed long before the rise of land vegetation. The researchers concluded that cohesive mixtures of sand and mud, containing about 30 to 45 percent mud, provided enough bank strength to support these stable channels. This suggests that geological factors—such as mud content and sediment supply—could confine a river just as effectively as modern roots.
Implications for Environmental Reconstructions
This reassessment of ancient river systems has significant consequences for how scientists model the past. If meandering rivers were more common in the early stages of Earth’s history, then previous estimates regarding the storage of nutrients, mud, and organic carbon may need to be revisited. This research also provides a useful framework for planetary geology. On Mars, where no vegetation has ever existed, scientists have observed sinuous channels and river deposits. The Stanford study suggests these features could be explained by non-biological cohesion, such as chemical cement or ice, and the specific ways unvegetated bends migrate across a landscape.
Pro Tip: When analyzing river deposits, look for the specific geometry of sediment-accretion directions. Downstream-migrating bends in barren environments create distinct signatures that differ from the lateral growth patterns seen in modern, vegetated floodplains.
Frequently Asked Questions
Does this study mean plants are not important for river stability? No. While the study proves that meanders can form without plants, vegetation still plays a role in modern systems. It slows down typical rates of meander growth and floodplain-soil reworking by as much as an order of magnitude. Why were these meanders missed in the geological record? Geologists traditionally used the variety of sediment-accretion directions as a proxy for sinuosity. Because barren meanders move primarily downstream, they produce a narrow range of directions that fits the traditional definition of a braided river, leading to misclassification. What does this mean for climate change modeling? Accurately classifying ancient rivers is essential for understanding how carbon was stored and transported across early continents. If meandering floodplains were more widespread than previously thought, models of early sediment cycles may require revision. *** *Have questions about how geological history impacts modern climate models? Join the discussion in the comments below or subscribe to our newsletter for the latest updates on Earth science research.*
Update (July 20, 2026)
according to spacedaily.com, the study did not excavate ancient S-shaped channels but used modern rivers to show why meanders might have been under-recognized in pre-plant rock records. it clarifies that vegetation caused a 62% increase in inferred flow-direction variance, not curvature, and highlights barren rivers in the Great Basin and Altiplano-Puna Plateau as examples.
the paper emphasizes that the traditional view linked pre-plant meandering rarity to unstable banks, but evidence like desert meanders and ancient single-thread rivers challenged this. the study’s contribution is explaining why these patterns remained hard to identify, using modern bends to reveal misclassification risks in geological records.