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Once upon a time,
South America lived harmoniously alongside Africa
until a crack in the Earth
drove the two continents apart.
This breakup began about 200 million years ago
during the separation of the supercontinent
known as Pangaea.
Their proximity back then
explains why the same plant fossils and reptile fossils,
like the Mesosaurus,
can be found on the South American east coast
and African west coast.
However, this evidence does not account for
how the continents moved apart.
For that, we'll need to take a close look
at the earth below our feet.
Though you may not realize it,
the ground below you is traveling across the Earth
at a rate of about 10 cm/year,
or the speed at which your fingernails grow.
This is due to plate tectonics,
or the large-scale movement of Earth's continents.
The motion occurs within the top two layers
of the Earth's mantle,
the lithosphere and asthenosphere.
The lithosphere,
which includes the crust and uppermost mantle,
comprises the land around you.
Beneath the lithosphere
is the asthenosphere
the highly viscous but solid rock portion
of the upper mantle.
It's between 80 and 200 km
below the Earth's surface.
While the asthenosphere wraps around the Earth's core
as one connected region,
the lithosphere is separated on top
into tectonic plates.
There are seven primary tectonic plates
that compose the shape of the planet we know today.
Like the other smaller tectonic plates,
the primary plates are about 100 km thick
and are composed of one or two layers:
continental crust and oceanic crust.
Continental crust forms the continents
and areas of shallow water close to their shores,
whereas oceanic crust forms the ocean basins.
The transition from the granitic continental crust
to the basaltic oceanic crust
occurs beyond the continental shelf,
in which the shore suddenly slopes down
towards the ocean floor.
The South American Plate is an example
of a tectonic plate made of two crusts:
the continent we know from today's map
and a large region of the Atlantic Ocean around it.
Collectively comprising the lithosphere,
these plates are brittler and stiffer
than the heated, malleable layer of the asthenosphere below.
Because of this,
the tectonic plates float on top of this layer,
independently of one another.
The speed and direction in which these tectonic plates move
depends on the temperature and pressure
of the asthenosphere below.
Scientists are still trying to nail down
the driving forces behind this movement,
with some theories pointing towards mantle convection,
while others are examining
the influence of the Earth's rotation
and gravitational pull.
Though the mechanics have not been sorted out,
the scientific community agrees
that our tectonic plates are moving
and have been for billions of years.
Because these plates move independently,
a fair amount of pushing and pulling
between the plates occurs.
The first type of interaction
is a divergent boundary,
in which two plates move away from one another.
We see this in the Mid-Atlantic Ridge
between South America and Africa.
The next interaction is when two plates collide,
known as a convergent boundary.
In this instance, the land is pushed upward
to form large mountain ranges,
like the Himalayas.
In fact, the Indian Plate is still colliding
with the Eurasian Plate,
which is why Mount Everest
grows one cm/year.
Finally, there's the transform boundaries,
where two plates scrape past one another.
The grinding of the transform boundary
leads to many earthquakes,
which is what happens
in the 810 mile-long San Andreas Fault.
The moving Earth is unstoppable,
and, while a shift of 10 cm/year may not seem like a lot,
over millions of years our planet will continue
to dramatically change.
Mountains will rise,
shorelines will recede,
islands will pop up.
In fact, one projected map shows
the cities of Los Angeles and San Francisco
on top of each other.
Maybe South America and Africa
will come together again, too.
Only time will tell.
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TED-Ed:不斷在運動的地球 (The Pangaea Pop-up - Michael Molina)

13961 分類 收藏
Kevin Tan 發佈於 2018 年 1 月 13 日

影片簡介

兩百萬年前,地球的陸地板塊是聚合為一體的,而我們將當時連接在一起的陸地稱為「盤古大陸」。時至今日,「盤古大陸」已經被分離成了七大主要板塊,但是是什麼驅動這些板塊的移動呢?讓我們跟著影片,一起探索地球科學的奧秘吧!

1proximity0:24
proximity 作為名詞,有「相鄰」和「相近」的意思,可以解釋成空間或是時間上的相近。
Her house was in close proximity to a loud factory which made it difficult to sleep at night.
她家離一個噪音很大聲的工廠很近,因此她晚上都難以入眠。


*同場加映:
愛滋病病毒與流感 — 疫苗的策略 (Seth Berkley: HIV and flu - the vaccine strategy)


2account for something0:36
這個片語除了可以解釋為「對某事作出解釋」,也有「佔多少百分比」和「知道某人或某物的下落」的意思。
IKEA's restaurant business accounts for five percent of the company's total revenue.
宜家家居的餐廳收入佔公司總收入的百分之五。

The police authority claims that they have accounted for the two missing fugitives.
警方聲稱他們已經掌握兩名逃犯的下落。


*同場加映:
陳凱斯(Keith Chen):你的語言會影響你的儲蓄能力嗎? Could your language affect your ability to save money?


3mantle1:01
作為名詞的 mantle 有三種意思解釋,第一種是指「地函」,它是地殼和地核中間所夾雜的部分; 第二個解釋是「覆蓋層」; 第三種解釋是「某個地位或工作的責任」,特別用在這個責任是前一個身處這個地位或負責此項工作的人交給繼任者的情況下,也就是中文裡「衣缽」的意思,當要表示繼承或承接某人的衣缽時,常見的用法為 take on / assume / wear the mantle of something。
The scientists have been dedicated to the study of the Earth's mantle for many years.
科學家們致力於地球的地函研究好幾年了。

The mantle of snow covered the street.
一層白雪覆蓋了街道。

He has to take on the mantle of leadership because he is the only heir of their family business.
因為他是他們家族事業的唯一繼承者,所以他必須接下領導者的位置。


*同場加映:
歐巴馬於摩爾豪斯學院畢業致詞 (President Obama Delivers Morehouse College Commencement Address)


4uppermost1:07
uppermost 可以作為形容詞,也可作為副詞,意思是「最主要」或「最高的」。
There is corruption even in the uppermost levels of government.
就連政府的最高層也有貪腐發生。


*同場加映:
【TED-Ed】美國政府的三權分立 (How is power divided in the United States government? - Belinda Stutzman)


5nail down2:38
這個片語的意思是「全面的了解」或「確定;敲定」。nail 作為名詞是釘子,而作為動詞是用釘子釘的意思,所以 nail down 字面意思就是「釘下去」,因而延伸為「確定」或「敲定」的意思。
In order to start the project as soon as possible, we must nail down the details of the agreement today.
為了儘快開始這個專案,我們今天必須敲定好協議的細節。


看完影片後,你對板塊移動的成因是否更瞭解了呢?目前,有些科學家認為軟流圈地函的熱對流作用是板塊移動的原因,但也有人說地心引力也可能是地殼變動的成因。不管如何,我們可以確定的是,地球的面貌不停在改變,幾百萬年後的地球有沒有可能又回到「盤古大陸」時期的樣子呢?

文/ Sunny Yang

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