I'm glad you brought up the question of our investigations into the makeup of the Earth's interior.
我很高興你們提出我們進(jìn)入地球內(nèi)部的組成的調(diào)查的問題。
In fact, since this is the topic of your reading assignment for next time, let me spend these last few minutes of class talking about it.
事實(shí)上，由于這是你們下次閱讀作業(yè)的課題，讓我花上這最后幾分鐘的課堂時(shí)間來談一下它。
There were several important discoveries in the early part of this century that helped geologists develop a more accurate picture of the Earth's interior.
本世紀(jì)早期有一些重要的發(fā)現(xiàn)，能夠幫助地質(zhì)學(xué)家開發(fā)出一個(gè)更精確的地球內(nèi)部的圖片。
The first key discovery had to do with seismic waves.
第一個(gè)關(guān)鍵的發(fā)現(xiàn)不得不同地震波相關(guān)。
Remember they are the vibrations caused by earthquakes.
要記得他們是地震引起的震動(dòng)。
Well, scientists found that they traveled thousands of miles through the Earth's interior.
好的，科學(xué)家發(fā)現(xiàn)他們穿過地球內(nèi)部通行了數(shù)千英里。
This finding enabled geologists to study the inner parts of the Earth.
這個(gè)發(fā)現(xiàn)是的地質(zhì)學(xué)家更夠研究地球的內(nèi)部。
You see, these studies revealed that these vibrations were of two types: compression or P waves and shear or S waves.
你看，這些研究顯示這些震動(dòng)是兩種類型：漲縮波或者說P波和畸變波或者說S波。
And researchers found that P waves travel through both liquids and solids, while S waves travel only through solid matter.
同時(shí)研究人員發(fā)現(xiàn)P波能穿行液體和固體兩種，而s波只能穿行固體物質(zhì)。
In 1906, a British geologist discovered that P waves slowed down at a certain depth but kept traveling deeper.
在1906年，一個(gè)英國地質(zhì)學(xué)家發(fā)現(xiàn)P波在一定的深度會(huì)減速，但是會(huì)繼續(xù)穿行更深。
On the other hand, S waves either disappeared or were reflected back, so he concluded that the depth marked the boundary between a solid mantle and a liquid core.
另一方面，S波要么消失，或者被反射，所以他推斷這個(gè)深度標(biāo)示了固態(tài)地幔和液態(tài)地核的界限。
Three years later, another boundary was discovered that between the mantle and the Earth's crust.
三年后，另一個(gè)分界線被發(fā)現(xiàn)，是在地幔和地殼之間。
There's still a lot to be learned about the Earth.
關(guān)于地球還有許多要學(xué)習(xí)的。
For instance, geologists know that the core is hot. Evidence of this is the molten lava that flows out of volcanoes. But we're still not sure what the source of the heat is.
舉例來說，地質(zhì)學(xué)家知道地核是熱的。這點(diǎn)的證據(jù)是火山中流出的熔巖。但我們依然不知道熱源是什么。
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