托福official4听力lecture3 Moving Rocks原文解析+翻译音频

[00:00.00]Narrator: Listen to part of a lecture in a geology class.
[00:05.90]MALE PROFESSOR: Now, we've got a few minutes before we leave for today. [00:08.43]So I'll just touch on an interesting subject that I think makes an important point. [00:12.49]We've been covering rocks, and different types of rocks, for the last several weeks, [00:17.30]but next week we're going to do something a bit different. [00:20.14]And to get started I thought I'd mention something that shows how, uhh, as a geologist, you need to know about more than just rocks and the structure of solid matter.[00:29.07]Moving rocks. You may have heard about them.[00:31.89]It's quite a mystery.
[00:34.27]Death Valley is this desert plain...a dry lakebed in California, surrounded by mountains, and on the desert floor are these huge rocks... some of them hundreds of pounds... [00:44.32]and they move! [00:45.43]They leave long trails behind them—tracks you might say—as they move from one point to another. [00:51.08]But nobody has been able to figure out how they're moving because no one has ever seen it happen.
[00:56.61]Now there are a lot of theories, but all we know for sure is that people aren't moving the rocks. [01:02.41]There're no footprints, no tire tracks, and no heavy machinery—like a bulldozer, umm nothing was ever brought in to move these heavy rocks.[01:10.73]So what's going on?
[01:13.79]Theory number one: wind. [01:16.46]Some researchers think powerful, um, windstorms might move the rocks. [01:21.27]Most of the rocks move in the same direction as the dominant wind pattern, from southwest to northeast. [01:27.61]But some, and this is interesting, move straight west, while some zigzag... or even move in large circles. [01:34.81]Hmmm... how can that be? [01:37.33]How 'bout wind combined with rain? [01:40.71]The ground of this desert is made of clay. [01:43.70]It's a desert, so it's dry. [01:45.69]But when there is the occasional rain, the clay ground becomes extremely slippery. [01:50.45]It's hard for anyone to stand on, walk on.
[01:53.41]Some scientists theorize that perhaps when the ground is slippery, the high winds can then move the rocks.[01:59.72]There's a problem with this theory. [02:01.80]One team of scientists flooded an area of the desert with water, then tried to establish how much wind force would be necessary to move the rocks. [02:10.61]And get this, you need winds of at least 500 miles an hour to move just the smallest rocks, [02:16.83]and winds that strong have never been recorded, ever,[02:20.74]not on this planet. [02:22.19]So I think it's safe to say that that issue's been settled.
[02:26.05]Here's another possibility. Ice. [02:29.08]It's possible that rain on the desert floor could turn to thin sheets of ice when temperatures drop at night.[02:35.96]So, if rocks uh become embedded in ice, uh, OK, could a piece of ice with rocks in it be pushed around by the wind? [02:45.65]But there's a problem with this theory too. Rocks trapped in ice together would have moved together when the ice moved. [02:54.29]But that doesn't always happen. The rocks seem to take separate routes.
[02:58.62]There are a few other theories. Maybe the ground vibrates, [03:01.34]or maybe the ground itself is shifting, tilting. [03:06.20]Maybe the rocks are moved by a magnetic force. [03:09.50]But sadly, all these ideas have been eliminated as possibilities. [03:13.46]There's just no evidence.[03:15.21]I bet you're saying to yourself, well, why don't scientists just set up video cameras to record what actually happens?
[03:22.32]Thing is, this is a protected wilderness area, [03:25.59]so by law, that type of research isn't allowed. [03:28.28]Besides, in powerful windstorms, sensitive camera equipment would be destroyed. [03:33.21]So why can't researchers just live there for a while until they observe the rocks moving? [03:38.50]Same reason. [03:39.73]So where are we now? [03:41.65]Well, right now we still don't have any answers.
[03:44.65]So all this leads back to my main point. You need to know about more than just rocks as geologists. [03:51.26]The researchers studying moving rocks, [03:54.25]well they combined their knowledge of rocks with knowledge of wind, ice, and such, uhh not successfully, not yet,
[04:01.19]but y'know... they wouldn't even have been able to get started without, umm... earth science understanding. Knowledge about wind . . . storms . . . you know, meteorology. [04:11.38]You need to understand physics. [04:13.74]So for several weeks, like I said, we'll be addressing geology from a wider perspective.[04:18.83]I guess that's all for today. [04:20.68]See you next time.