Study: Rivers meandered before plants existed

A new study challenges a long-standing geological assumption that rivers require vegetation to form meandering channels. Stanford University researchers published findings in August 2025 demonstrating that rivers carved S-shaped curves long before plants existed on land. The study, led by a team from Stanford's School of Earth, Energy & Environmental Sciences, analyzed ancient river deposits in Namibia and Australia, dating back over 2.5 billion years—predating the emergence of terrestrial vegetation by more than a billion years. Using satellite imagery and field observations, the researchers identified preserved meander patterns in rocks from the Archean Eon, when Earth's surface was largely barren. The discovery overturns a decades-old teaching that rooted plants were essential for stabilizing riverbanks and enabling meander formation. Instead, the findings suggest that microbial mats or other early life forms, or even purely physical processes like sediment cohesion, could have produced the same effect. The study's lead author, a Stanford postdoctoral researcher, noted that the work forces a re-evaluation of how ancient landscapes evolved and how rivers shaped early Earth environments. The research also has implications for understanding river systems on other planets, such as Mars, where meandering channels have been observed but no vegetation exists. The team plans to further investigate the role of microbial life in ancient river dynamics and to apply their findings to planetary geology. The study was published in the journal Geology.