Placeholder Image

Subtitles section Play video

  • How old is the Earth?

  • Well, by counting the number of isotopes

  • in a sample of rock

  • that's undergone radioactive decay,

  • geologists have estimated the Earth's birthday,

  • when it first formed from a solar nebula,

  • to be 4.6 billion years ago.

  • But just how long is that really?

  • Here's some analogies

  • that might help you understand.

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

  • until the present day

  • as a single calendar year.

  • On January 1st, the Earth begins to form.

  • By March 3rd, there's the first evidence

  • of single-celled bacteria.

  • Life remains amazingly unicellular until November 11th

  • when the first multicellular organisms,

  • known as the Ediacaran fauna, come along.

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

  • is the Cambrian Explosion of life,

  • a major milestone,

  • when all of the modern phyla started to appear.

  • On December 10th at 1:26 p.m.,

  • the dinosaurs first evolve

  • but are wiped out by an asteroid

  • just two weeks later.

  • On December 31st, the mighty Roman empire

  • rises and falls in just under four seconds.

  • And Columbus sets sail

  • for what he thinks is India

  • at three seconds to midnight.

  • If you try to write the history of the Earth

  • using just one page per year,

  • your book would be 145 miles thick,

  • more than half the distance

  • to the international space station.

  • The story of the 3.2 million year-old

  • Australopithecine fossil known as Lucy

  • would be found on the 144th mile,

  • just over 500 feet from the end of the book.

  • The United States of America's Declaration of Independence

  • would be signed in the last half-inch.

  • Or if we compared geologic time

  • to a woman stretching her arms

  • to a span of six feet,

  • the simple act of filing her nails

  • would wipe away all of recorded human history.

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

  • from the moment you're born

  • to your first day of high school.

  • Your first word,

  • first time sitting up,

  • and first time walking

  • would all take place while life on Earth

  • was comprised of single-celled organisms.

  • In fact, the first multicellular organism

  • wouldn't evolve until you were 12 years old

  • and starting 7th grade,

  • right around the time

  • your science teacher is telling the class

  • how fossils are formed.

  • The dinosaurs don't appear

  • until three months into 8th grade

  • and are soon wiped out right around spring break.

  • Three days before 9th grade begins,

  • when you realize summer is over

  • and you need new school supplies,

  • Lucy, the Australopithecine, is walking around Africa.

  • As you finish breakfast

  • and head outside to catch your bus

  • 44 minutes before school,

  • the Neanderthals are going extinct throughout Europe.

  • The most recent glacial period

  • ends as your bus drops you off

  • 16 minutes before class.

  • Columbus sets sail 50 seconds before class

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

  • The Declaration of Independence is signed

  • 28 seconds later

  • as you look for an empty seat.

  • And you were born 1.3 seconds before the bell rings.

  • So, you see, the Earth is extremely,

  • unbelievably old

  • compared to us humans

  • with a fossil record

  • hiding incredible stories to tell us about the past

  • and possibly the future as well.

  • But in the short time we've been here,

  • we've learned so much

  • and will surely learn more

  • over the next decades and centuries,

  • near moments in geological time.

How old is the Earth?

Subtitles and vocabulary

Operation of videos Adjust the video here to display the subtitles

B1 TED-Ed earth single celled celled grade columbus

【TED-Ed】Four ways to understand the Earth's age - Joshua M. Sneideman

  • 1373 186
    Viola posted on 2013/11/30
Video vocabulary