How We Proved An Asteroid Wiped Out The Dinosaurs | Big History Project

How We Proved An Asteroid Wiped Out The Dinosaurs | Big History Project


WALTER ALVAREZ: I think
most people are fascinated by murder mysteries. Well, about 30 years ago, I stumbled onto
a great murder mystery and the victims
were the dinosaurs. And the question was, what had caused them
to become extinct? Well, I was working
on a different project in Italy at that time
and sort of stumbled on the… on the level in the rock record where the dinosaurs
became extinct. Only there weren’t
any dinosaurs. There were tiny little
single-celled organisms called forams. This is a piece of our beautiful
pink limestone from Italy. And, if you look
really closely down here, you can see there are lots
of little specs about the size of sand grains,
and those are forams– single-celled fossils– fossils
of single-celled organisms that almost became extinct at the same time
the dinosaurs did. And here’s what it looks like
in a piece of rock in the field. So this is the last bed
of the Cretaceous, which is the time
that the dinosaurs were around. And if you look closely again,
you can see these little sand-sized specs
which are microfossils. This is the first bed
of the tertiary which is the time that was
after the dinosaur extinction and after the almost extinction
of the forams because the– once that you
can see with your naked eye became extinct, up here,
there are forams, but they’re too small to see. And this is a level of
clay in between the two. Now, it’s hard now
because this piece of rock has been encased in plastic. But we got interested in that
clay and what it might tell us. And we, as a group here at
Berkeley, it was my father, Luis Alvarez
who was a physicist, and I’m the geologist
in the group and Frank Asaro and Helen Michel
who were two nuclear chemists who could measure elements
at extremely low concentrations. And we decided to measure
the element iridium which is a marker
for extraterrestrial material. And we had expected
to find either no iridium or a very small amount
of iridium in that level. But I’ll never forget the day
that I got a telephone call from Frank, and Frank said,
“Something is wrong. There is far more
iridium in this clay “than we had been–
than any of our ideas would have predicted.” Something was wrong and
it turned out to be the clue that led to solving
the extinction of the dinosaur murder.
But it took quite a while to figure out
what that clue meant. What we finally figured out
was that it was telling us that a comet or an asteroid
the size of Mount Everest had hit the earth
on a particular day, 65 million years ago
and caused the extinction, not only of dinosaurs
and the forams, but of many other different
kinds of plants and animals. For example, like this
coiled-shelled ammonite. This group also became
extinct at that same time. And we gradually came to realize how much energy there
is in a very big rock falling from the sky. There would have been
enough energy to blow debris and rocks and dusts
and chunks of things from the impact site
all over the entire earth. And when it landed
on the top of the atmosphere, there were so much of
it that it would have made the earth cold and
dark for probably months so that plants
would stop growing and animals wouldn’t have food
and many groups became extinct. Not all, obviously,
because we’re still around. Well, this was a
catastrophic explanation for the extinction and that did not sit
well with most geologists and paleontologist
at the time about 1980 because we were used to
thinking of all changes in the Earth’s history
as being slow and gradual and this was the exact opposite. So there was a huge debate. It went on for ten years,
from 1980 to 1990. And meanwhile, people
looked for other evidence and they found other
evidence of impact, like, spherules
and shocked quartz. And all that time,
all during that ten years, the big unanswered question was, where was the crater
that would have been produced when this comet or
asteroid fell from the sky? Finally, in 1991, the great
breakthrough took place. We learned about a huge crater below the surface
of the Yucatan Peninsula that the Mexican oil geologists
had discovered. It’s the biggest impact crater
that’s formed on this planet in the last billion years. And the Mexicans drilled it
and here’s what they found. So this is a thin
slice out of a circular core. And this is rock that was melted
by the heat of impact. And you can tell
that it was melted by impact because the mineral
grains in it have features that only form with
very great shock effects And so we then had
evidence for a giant impact. We could tell that it was
approximately the right age but you couldn’t be sure
of exactly the right age. So some of us went and
looked at other outcrops in other parts of Mexico
and we found the debris from this impact–
from this crater– at exactly the level
of the extinction, right at the boundary
between the Cretaceous and the tertiary. And so that was the evidence
that can… has convinced almost all
geologists and paleontologists that it was indeed an impact
that caused the mass extinction. Well, this is a pretty good
example of how science works and how geologists
and paleontologists figure out what
happened in earth history. You start with some unexpected
evidence like the iridium. Then you make up a theory
to try to explain it. And then other people
get interested, and they look for other
evidence like spherules and shocked quartz. And there’s a great debate
because that’s the way we work these things out in science. And finally, along comes the most
convincing evidence of all– in this case the crater, which
convinces virtually everyone. And so that’s the story of how geologists
and paleontologists solved what may have been
the greatest murder mystery in all of Big History.

Randy Schultz

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11 thoughts on “How We Proved An Asteroid Wiped Out The Dinosaurs | Big History Project

  1. diam911 says:

    really well explained. I liked the last portion on "how does science work" very much as well.

  2. Tony Hood says:

    …there are pyramids and temples buried beneath limestone melt rock, on the Yucatan. The same limestone to form the Ozarks and was ejected from beneath the Mediterranean, which was part of the Tethys…

    …these man-made structures, now in rock, are proof that many civilizations were wiped out from a major cataclysm, with enough force to split up a supercontinent. The only object to produce such force, with enough mass, weight, volume, density,… electromagnetic repulsion, and in orbit, would be the Moon…

    13kya at the YDB the Moon impacted this planet…
    10.5kya a comet hit the Hudson bay..
    200 years ago a sungrazer C/1811F1caused a mini-ice age…

    …please go over every detail, [discussion, link,…] – https://www.linkedin.com/pulse/phaulty-fysics-shock-dynamics-impact-mechanics-devolution-tony-hood

  3. Wes Mahan says:

    I see there is one "down" vote. So a Christian Young Earth Creationist viewed this video, and voted on his stupid ignorance. Well done, dunce.

  4. twistedlot says:

    Chicxulub crater = smoking gun

  5. The Sad Ghost says:

    Diamond12224…..

  6. J CS says:

    Nemesis. Planet X.

  7. Rui Alexandre says:

    Would it be possible to add portuguese (from Portugal) subtitles to this video?

  8. Someone Just says:

    The hot chick hitting on Ross brought me here

  9. Sai mohit Pasupuleti says:

    you explained really well

  10. Indigo Soldier says:

    I’m dumb

  11. King Starsky says:

    a very well done video!

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