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.
【視聽版科學(xué)小組榮譽出品】
evolution constrain stabilized erode constant risk
樹木造就的現(xiàn)代河流 今天的河流有著高高的泥堤、沙堤和彎道。但是它們在樹類植物進(jìn)化前并不是這樣子的。大概33億年前，河流才開始有它們現(xiàn)在的這種樣子。在那之前，古老的水域很寬，而且很淺，除了山之外沒有什么可以限制它們。引自《自然地球科學(xué)雜志》。 研究人員查閱了400多份地球巖石記錄，并走訪了近70個研究現(xiàn)場。研究發(fā)現(xiàn)巖石中河道的形成，也就是現(xiàn)代河流的跡象直到石炭紀(jì)（也就是樹類植物進(jìn)化后）才開始出現(xiàn)。因為越大的植物需要扎根更深，這就使得它們需要鞏固河岸，強迫河道變得更窄。這些深深的根系促成了不易腐蝕的黏土的形成。 研究人員認(rèn)為，這一切的工程都是樹木的功勞。因為河岸為樹木提供便利的水源，且洪水泛濫的可能性小，這也正是我們?nèi)祟愊胍?。許多我們最好的城市都是沿江的。我們需要感謝樹木為我們帶來的這些。