How do we know an asteroid hit Earth 66 million years ago?
JACKIE FAHERTY (Senior Scientist, Division of Physical Sciences, American Museum of Natural History): How do we know an asteroid hit Earth 66 million years ago?
[FAHERTY on screen. Text reads: “How do we know an asteroid hit Earth 66 million years ago?”]
[MUSIC] [BOOM]
[The logo for the American Museum of Natural History appears above text that reads: “Space Vs Dinos”. In the background, an illustration of an asteroid and a dinosaur skull and bones. Slide to FAHERTY on screen. Text reads: “Jackie Faherty, astrophysicist”]
FAHERTY: Here at the American Museum of Natural History,
[A drawing of the Museum’s façade slides behind FAHERTY.]
FAHERTY: we’re pretty well known for two things, and that’s space and dinosaurs.
[A line connects Saturn and the dinosaur. The line pulls open into a projector screen.]
FAHERTY: And there’s one unifying tie between the two.
[A line connects Saturn and the dinosaur. The line pulls open into a projector screen.]
FAHERTY: 66 million years ago there’s very strong evidence that a giant asteroid hit the Earth
[Text reads: “66 million years ago”. An asteroid hits Earth with dinosaurs standing beneath it.]
FAHERTY: and caused a mass amount of change on this planet
[An illustrated Sun is covered with clouds. The reading in a thermometer drops down. Flames leap up with burning trees in the background.]
FAHERTY: which led to the extinction of the dinosaurs.
[A triceratops skull and a sauropod skull appear. Text reads: “*Non-avian dinosaurs”. A bird flies down, it says via text: “what the heck, guys”. FAHERTY appears on screen.]
FAHERTY: How do we know that happened? Well in the 1980s,
[A circle appears next to FAHERTY with a photo of a man wearing glasses.]
FAHERTY: a geologist named Walter Alvarez uncovered, with the help, actually of his physicist, Nobel Prize-winning father,
[Circle expands to reveal man wearing glasses standing next to a rock face, and another older man. A line indicates the younger man is Walter Alvarez, and the older man is Luis Alvarez. A line appears between the two. Text reads: “Father-son bonding”]
FAHERTY: that right at the K-Pg boundary
[Behind the two men in the photo, a line appears in the rock. The camera tilts and zooms into this line. Text reads: “K-PG Boundary.” Smaller lines appear horizontally on either side of the dark line in the middle. Text indicates that rock above the dark line is younger, rock below the dark line is older, and the dark line is from 66 million years ago.]
FAHERTY: which was the point of dinosaurs’ extinction,
[The letters “K” and “PG” fly off of “K-PG Boundar” to indicate that PG stands for “Paleogene Period” which is above the boundary and K stands for “Cretaceous Era” which is below the boundary. Dinosaur skulls fill in below the line in the Cretaceous Era portion of the screen.]
FAHERTY: you had a particularly strong amount of what’s called iridium.
[A circle expands in the center of the screen filled with an image of light silver-looking beads. Text reads: “Iridium.” FAHERTY appears on screen.]
FAHERTY: And iridium, which is atomic number 77 on your periodic table,
[The element symbol for Iridium appears next to FAHERTY.]
FAHERTY: is mostly found in high quantities in asteroids.
[The iridium symbol and more iridium symbols attach themselves to an asteroid.]
FAHERTY: In the Earth we can find it but it’s locked further down in the Earth.
[One iridium symbol appears over a globe, and it scales down to the center of the globe.]
FAHERTY: When you find a lot of iridium, that’s a bit of a smoking gun that you’ve got the signature of an asteroid impact.
[A dark band is speckled with green dots. A magnifying glass passes over it and lands on a post-it note that reads: “It was me. – asteroid.” [CHUCKLE] FAHERTY appears on screen again.]
FAHERTY: So the theory was put out there that an asteroid impact was the reason that the dinosaurs were extinct.
[An asteroid [ROARS] above a generic landscape and oceanscape. A white light fills the screen.]
FAHERTY: So if something hits you would expect there to be a crater.
[An illustrated crater spins slowly. It slowly fades while a boat appears, sailing in a circle.]
[RADAR SOUNDS + OCEAN SOUNDS]
FAHERTY: Now around the same time that the theory was put out there, there were oil exploration surveys that were ongoing in the Yucatan Peninsula.
[The camera pulls back to reveal the boat in the Gulf of Mexico, north of the Yucatan Peninsula of Mexico.]
FAHERTY: By chance, they uncovered
[Camera zooms into the tip of the Yucatan Peninsula. A dotted line circle is drawn in the western coast of the tip of the peninsula.]
FAHERTY: what’s now called the Chicxulub Impact Basin which is the right size and had the right chemical composition around it
[Text appears: “Chicxulub impact basin.” Diameter of the circle reads: 93 miles / 150 km. FAHERTY reappears.]
FAHERTY: that we think that that is the site of the giant impact that led to the extinction of the dinosaurs.
[Rotating globe flies in from the bottom left.]
FAHERTY: The thing is that asteroids
[An asteroid flies in from the bottom right.]
FAHERTY: or parts of asteroids, dust of an asteroid,
[Small pieces of rock fly in from the bottom right and even smaller dots come into focus all over the screen.]
FAHERTY: we actually get hit by it all the time. Anytime you see a shooting star,
[Two human silhouettes look over trees at shooting stars. They [GASP] and point.]
FAHERTY: you’re seeing a bit of a piece of rock that’s burning up in your atmosphere.
[Closeup of the shooting star reveals a small rock in the middle growing orange and then disintegrating and blowing off. FAHERTY appears on screen.]
FAHERTY: The ones that we worry about are the big ones. The one that knocked out the dinosaurs was six miles in diameter.
[An asteroid appears in a circle to her right. It is measured to be “6 miles (10 kilometers)”]
FAHERTY: That kind of impact – it happens, but it’s far more rare. And unlike the dinosaurs,
[A long-necked dinosaur and a triceratops fall from the top of the screen and look confused at a telescope. The camera pans right and we see a modern observatory looking up with a [CLANK].]
FAHERTY: astronomers are ready and watching for one that might be hazardous.
[Above it, an asteroid appears. A tennis racket comes out and [WHACKS] the asteroid away.]
[Credits roll. FAHERTY appears in the bottom right of the screen.]
FAHERTY: If you want to hear more about what exactly the asteroid did to the dinosaurs, then click here and hear from Team Dinos on the asteroid and dinosaurs themselves. Thanks everybody for watching, tune in for more videos where Team Space will yet again take out Team Dinosaur.
One theory for why the dinosaurs went extinct is that an asteroid hit Earth at the end of the Cretaceous period. But since no one was alive to see it, how can we know that it really happened? Astrophysicist Jackie Faherty reveals how clues found in sedimentary rock and on the ocean floor have helped scientists piece together this millennia-old mystery.
If you want to learn more about the effect an asteroid impact would have had on life on Earth during the Cretaceous, watch this week’s Dinosaur video.