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The Meandering-River Paradox of Earth and Mars

The Paleozoic Era (~541-252 million years ago) was a period of dramatic change at the surface of the Earth, starting with a rapid diversification of animals in the oceans, continuing through the colonization of land, and ending with the largest known mass extinction in Earth’s history. In addition to significant biological events, one of the most fundamental changes in the Paleozoic sedimentary record lies in the architecture of fluvial sandstones; although most fluvial deposits that predate the Paleozoic appear to have been formed by wide, shallow, and sandy braided rivers, a significant record of single-threaded sinuous channels emerge during the Paleozoic and culminate with the appearance of single-thread meandering channels with preserved muddy bank deposits. Today, meandering rivers are the most widespread type of river in Earth’s lowlands. Because this relatively rapid change in river morphology coincides with the advent and rapid diversification of land plants, it has been suggested that plant life sparked the rise of river meanders by strengthening riverbanks. However, this hypothesis is at odds with the presence of early meandering-river deposits on Mars and the recently recognized abundance of meandering rivers in unvegetated clay-rich basins on Earth today.