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【科学60秒】树木造就的现代河流
听力简介:
Rivers today have high muddy banks, sandbars and bends. But they didn’t always look that way. Because it wasn’t until the [--1--] of tree-like plants, some 330 million years ago, that rivers were corralled into their current form. Before that, ancient waters flowed wide and shallow over the land, with little to [--2--] them other than mountains. So says a study in the journal Nature Geoscience.
Researchers looked through over 400 studies of the Earth’s rock record, and visited nearly 70 field sites. And they found that channel formations in the rock—a signature of modern rivers—didn’t appear until the Carboniferous period, when tree-like plants evolved. That’s because larger plants needed deeper roots, which [--3--] river banks and forced rivers into narrower paths. And deep roots helped form sticky clays, which are harder to [--4--].
All this engineering was to the trees’ advantage, the researchers say. Because river banks provide trees with easy access to water, without the [--5--] of flooding. Pretty much what we humans want. Many of our greatest cities formed along river banks—for which we might have trees to thank.
【视听版科学小组荣誉出品】
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