Listen to part of lecture in a Geology Class.
About 30 years ago, a geologist named
Eward Edward Cotter, that's "C-O-T-T-E-R", published a paper that contained a very interesting hypothsis hypothesis.
He was studying ancient rivers in the North American
NuttenShame mountain chain. And he noticed , there was that about 450 million years ago, rivers started to behave differently. Before then, rivers were white wide, shallow and straight. But after that time, they became deeper and had more curves. They becaming became increasingly me andering meandering and that's actually how rivers behave to the state this day. So, why might this change happened?
were was some kind of climb climate shift?
Well, lot of
time machivedclimate shift happened since then.
Was the change the worldwide? or just
netoo go other in that geographical area.
cutter Cotter speculated that rivers changed world wide, but he couldn't prove it. Because he only had evidence from the one, North American mountain shame chain. But he's his studies gave an idea about why rivers started to change. He had pophysis hypothesized it and had to this with seprate spread of plant life on Earth.
So, there was no plant life
the four before four hundred fifty million years ago?
Very little accrording to
phasor fossil records. Anyway, geologists were entry intrigued by the thyposis hypothesis, which clamed claims that as plenty evolved and spread, they had affect an effect on the terrian and rivers. In the past 30 years, more studies have been done. And now we have a lot of data about river systems from around 450 million years ago, from all over the world.
In a recent study, a couple of researchers gathered together the exsiting data and combined them with their own new filed data to get a c
uplpe of hansor of picture comprehensive picture of the situation.
Their study was specifically design to identify changes in the shapes of rivers during the time period when
vatutation vegetation was evolving.
And when the reseachers compare the data about the river shapes with that they have collected about plant life from the same period, the data seem to prove
cluttersyposis Cotter's hypothesis.
Okay, but how did plant
that sytrivers life affect rivers?
Well, in order to answer that question, we need to look at the geological evidence.
You see, as rivers flow, they live
near layers of settlement sediment behind that of actually eventually fossilized. The containt content, figness thickness, and shape of these folllize fossilized layers and rocks give us information about how rivers flowed. The early astracter earliest records from 500 million years ago show that the settlement sediment in river deposits was largely composed of course coarse grand grain of sand and daval gravel. A va That tells us that the rivers weren't defined, they were very shallow, and wide, almost like floods.
But around the time of the
arise rise of plant life, the content of those settlement sediment layers began to change. Of course, The coarse grains began much finer. And we see evidence of mud. This suggests that plants promoted the preservation of mud when they sent their roots into the ground. The root helped to reinforce the ground which in term turn allowed for the creation of river banks.
And we also see evidence of process called
latter lateral accretion ecretion.
ecretion accretion happens when water flows around curves a curve aband or bend in a the riverbed. Now the speed of the flow on the outside of the been bend is fatisted fastest, and slowest on the inside of the bean bend. This sets up was what's called a secondary flow across the river buttom. The fasforning fast-flowing water in on the outside of bend, digs out that material from the riverbank and pushes this material laterly laterally across the buttom, and get supposed deposited on the other side of the river, I mean on the inner side of the bend.
So, when we see in the
settlement sediment layers. Evidence so latteral creation lateral accretion, it rose erosion on one sides and deposits on the other, that's an indicator that mederly a meandering river ended existed.
what into according to the study, strong evidence of letteral lateral accretion recreation appears emegialogical in the geological record. At the same time, that there's also evidence of plants with underground root systems. This suggests that plants promoted the developmoter development of modern rivers by creating stable banks, which resulted ??? in the flow of water in sigle miendaring meandering channels.
So, it looks like the researchers
??? were able to prove the hypothesis.
Well, there's no denying. That's the study
proosense presents a very strong case. But some questions about this hypothesis remain. For example, it's well known that in on other plants like Mars, there's clear evidence of endmiRivers meandering rivers. But is there evidence of vegetation on Mars? I think it's not.
不过有些证据说明了“lateral accretion”的情况，准确的来讲，如果我们想通过fossil得知一条河流是直的还是弯曲的，我们主要看沉积物。而lateral accretion会造成河流的一侧或有堆积，一侧被侵蚀的状态。原理在于完全的河道，外流速度比内流速度快，所以外流容易把河床的东西给翻上来，并且外流的岸容易被侵蚀。这才是给弯曲河道定性的东西。在化石的状态下，你很容易发现，如果它原来是直的，你就不可能发现一边sediment多，一边少，所以，用这个方法来定性这个河道是弯的。
NuttenShamemountain chain 山链（这个怎么可能想到？）（除非在你耳边非常清晰地吐字出来） , there wasthat about the statethis day netoo go otherin that geographical area the fourbefore Of course,The coarse I meanon the
- hypothesis 假设
- shallow 浅的
- curves 曲线
- meandering 弯曲
- climate shift 气候变化
- geographical 地域 （如果你写出来，我还可能认识这个单词）（现在看来，听清楚比听清楚更重要）（背单词的时候要更注重发音）
- speculated 推测
- fossil 化石
- intrigue 阴谋
- intrigued 感兴趣 （这个单词我就没查到）
- terrain 地形 （这个单词，玩Unity的话毕竟都知道terrain是什么）
- comprehensive picture 综合图片
- vegetation 植被
- sediment 沉淀
- coarse 粗
- gravel 碎石
- finer 更好
- bank 银行；岸
- lateral 侧
- lateral accretion 横向增生
- bend 弯曲
- laterally 横向地
- erosion 侵蚀
- meandering 弯曲
- it had to do with~ 与……有关 （口语里面表达与~有关，直接have to do with)
- a couple of researchers 几个研究人员 （这个不要想成是一对或几对，这个a couple of更接近于several）
- river banks 河岸
- express a reservation 表达一个“保留意见”
- reservation 保留意见；疑惑；