Well, by counting the number of isotopes

嗯，拿一顆歷經放射性衰變

in a sample of rock

的石頭樣本

that's undergone radioactive decay,

來計算同位素數量

geologists have estimated the Earth's birthday,

地質學家由太陽星雲的組成

when it first formed from a solar nebula,

推估地球的生日

to be 4.6 billion years ago.

約在四十六億年前

But just how long is that really?

但那到底是多久呢？

Here's some analogies

在這裡用類推法

that might help you understand.

幫助你了解

For example, let's imagine the entire history of Earth

舉例來說，讓我們想像一下到今天為止

until the present day

地球的完整歷史

as a single calendar year.

當作一個個別曆年

On January 1st, the Earth begins to form.

地球在一月一日開始成形

By March 3rd, there's the first evidence

三月三日時，出現單細胞細菌

of single-celled bacteria.

存在的首要證據

Life remains amazingly unicellular until November 11th

令人驚訝的是，直到十一月十一日

when the first multicellular organisms,

才出現第一個多細胞生物『軟體海洋物種』

known as the Ediacaran fauna, come along.

在那之前，仍是單細胞生物

Shortly thereafter, on November 16th at 6:08 p.m.

不久之後，十一月十六日的晚間六點零八分

is the Cambrian Explosion of life,

是寒武紀生物大爆發

a major milestone,

的主要里程碑

when all of the modern phyla started to appear.

所有的現代物種開始出現

On December 10th at 1:26 p.m.,

在十二月十日的下午一點二十六分

the dinosaurs first evolve

恐龍首先進化

but are wiped out by an asteroid

但卻在兩週後

just two weeks later.

被行星摧毀

On December 31st, the mighty Roman empire

十二月三十一日，強大的羅馬帝國

rises and falls in just under four seconds.

只在四秒之內由興盛到毀滅

And Columbus sets sail

哥倫布啟航

for what he thinks is India

尋找他心目中的印度

at three seconds to midnight.

卻從三秒到午夜

If you try to write the history of the Earth

如果你每年

using just one page per year,

試著只寫一頁地球史

your book would be 145 miles thick,

你的書會有145英哩的厚度

more than half the distance

比國際太空站

to the international space station.

一半的距離還多

The story of the 3.2 million year-old

320萬歲的靈長類動物

Australopithecine fossil known as Lucy

『露西』的故事可以在

would be found on the 144th mile,

144英哩處被找到

just over 500 feet from the end of the book.

只從書底算過來超過500英呎處

The United States of America's Declaration of Independence

美國的獨立宣言

would be signed in the last half-inch.

簽署在最後半吋處

Or if we compared geologic time

或者如果我們拿地質時間

to a woman stretching her arms

和女人伸直手臂

to a span of six feet,

到六呎的長度相比較

the simple act of filing her nails

她整理指甲的簡單動作

would wipe away all of recorded human history.

會把人類歷史擦掉

Finally, let's imagine the history of the Earth as your life:

最後，讓我們想像把地球史

from the moment you're born

當作從你出生到

to your first day of high school.

第一天上中學的生活

Your first word,

你的第一個字

first time sitting up,

第一次坐起來

and first time walking

和第一次走路

would all take place while life on Earth

生活在地球上都會發生

was comprised of single-celled organisms.

它是由單細胞生物所構成

In fact, the first multicellular organism

事實上，第一個多細胞生物

wouldn't evolve until you were 12 years old

並不會進化到你十二歲

and starting 7th grade,

開始國一生活

right around the time

左右的時間

your science teacher is telling the class

自然科學老師告訴班上同學

how fossils are formed.

化石如何形成

The dinosaurs don't appear

直到三個月後

until three months into 8th grade

恐龍才出現，當你進入國二

and are soon wiped out right around spring break.

大約寒假時就被摧毀

Three days before 9th grade begins,

在國三開始前的三天時間

when you realize summer is over

當你想到暑假要結束了

and you need new school supplies,

你需要補充學校用品

Lucy, the Australopithecine, is walking around Africa.

靈長類動物『露西』正步行到接近非洲之處

As you finish breakfast

當你吃完早餐

and head outside to catch your bus

出門搭公車

44 minutes before school,

抵達學校前的44分鐘

the Neanderthals are going extinct throughout Europe.

原始人在歐洲正全面滅絕

The most recent glacial period

當你下公車

ends as your bus drops you off

在上課前的十六分鐘

16 minutes before class.

最近代的冰河時期結束

Columbus sets sail 50 seconds before class

當你還在試著找正確的教室時

as you're still trying to find the right classroom.

哥倫布啟航於上課前五十秒

The Declaration of Independence is signed

當你找空座位時

28 seconds later

美國獨立宣言

as you look for an empty seat.

簽署在二十八秒後

And you were born 1.3 seconds before the bell rings.

而你出生於上課鈴響前的一點三秒

So, you see, the Earth is extremely,

如此，你可明白

unbelievably old

對照人類

compared to us humans

隱藏著過去和未來

with a fossil record

不可思議故事的

hiding incredible stories to tell us about the past

化石而言，地球是非常

and possibly the future as well.

令人難以置信的年老

But in the short time we've been here,

但是在短時間裡，我們一直在這

we've learned so much

學到了很多

and will surely learn more

在未來的幾十年、幾百年

over the next decades and centuries,

地質年代相近的時刻

near moments in geological time.

我們確信將會學習更多