The K-T boundary is found in sediment layers in many different parts of the world. Try again.

Correct! K-T is an abbreviation for Cretaceous (which in turn originates from the German word Kreide) and Tertiary. Select another correct answer. You selected all the correct answers.

Correct! In the film, the K-T extinction is dated at 65 million years ago. However, using new dating methods, scientists have revised the date to 66 million years ago. Select another correct answer. You selected all the correct answers.

Correct! Dr. Jan Smit points to the K-T boundary in the film and explains that below the boundary the marine ecosystem was healthy and just above it most organisms have died. The boundary coincides with an abrupt loss in biodiversity. Select another correct answer. You selected all the correct answers.

Correct! The geologic layers above (or younger than) the K-T boundary show a sharp, dramatic reduction in diversity and size of foraminifera—a clue that something catastrophic happened. Select another correct answer. You selected all the correct answers.

Geologic layers above the boundary were deposited later. The boundary represents a catastrophic change in the biological world. How would such a change affect biodiversity? Try again.

Geologic layers above the boundary were deposited later. The boundary represents a catastrophic change in the biological world. Would larger or smaller organisms be more likely to survive? Try again.

Recall that the boundary represents a catastrophic change in the biological world, and geologic layers above the boundary were deposited later. Try again.

The asteroid impact hypothesis came later, to explain the surprisingly high iridium levels Dr. Alvarez found in the K-T boundary layer. Try again.

The supernova explanation came later, as an alternate explanation of the surprisingly high iridium levels Dr. Alvarez found in the K-T boundary layer. (The supernova hypothesis was ruled out by the lack of plutonium.) Try again.

Correct! Iridium is deposited on Earth at a fairly constant rate. Dr. Alvarez thought that if the layer formed over many thousands of years, he might be able to detect enough iridium to be able to determine how long it took for the K-T boundary layer to form. Instead, iridium levels were 30 times greater than in the surrounding rock, prompting researchers to investigate alternate iridium sources. Select another correct answer. You selected all the correct answers.

Supernovas that occur sufficiently close to Earth to greatly impact life on the planet are extremely rare events. There is no evidence that any of the known mass extinctions were caused by supernovas. Try again.

Correct! The asteroid hypothesis was not immediately accepted because it didn’t fit preconceptions about how Earth evolved. Paleontologists were also slow to accept a hypothesis advanced by a physicist, using evidence from outside their discipline. Select another correct answer. You selected all the correct answers.

It’s true that there are foraminifera on both sides of the boundary. However, those above (after) the K-T boundary are much smaller and less diverse than those below (before). Such evidence is consistent with a catastrophic event like an asteroid impact. Try again.

Large dinosaur fossils disappear abruptly at the end of the Mesozoic. This evidence is consistent with a catastrophic event like an asteroid impact. Try again.

Correct! The element iridium is rare in Earth’s crust and relatively abundant in asteroids and comets. Because the K-T boundary contains an extremely high concentration of iridium, Dr. Alvarez and colleagues proposed that an Earth-crossing asteroid collided with the planet, and the fallout from this collision spread a layer of iridium across the globe. Select another correct answer. You selected all the correct answers.

The presence of plutonium-244 in the K-T boundary would be consistent with a supernova but not with an asteroid impact. Try again.

Correct! The extremely high pressure of an asteroid impact caused quartz grains at the impact site to shatter and fracture internally as they were blasted into the air. Shocked quartz particles are found at the K-T boundary at various distances from the impact site. Select another correct answer. You selected all the correct answers.

Correct! When the asteroid struck, some of the rock in Earth’s surrounding crust melted as it was ejected from the impact site. As these melted rock particles fell back to Earth and cooled, they formed glasslike objects called tektites. Select another correct answer. You selected all the correct answers.

Correct! The discovery of the crater tied together all the other evidence, showing that researchers had found a crater of the right size and age. Select another correct answer. You selected all the correct answers.

Tsunami deposits were evidence for an asteroid impact but not the critical piece of evidence. Try again.

While hunting for oil, Glen Penfield recorded features of a giant, buried crater. This was an important clue that led to actually finding the crater. Try again.

The spherules and shocked quartz provided evidence for an asteroid impact somewhere around the Gulf of Mexico, but not the critical evidence. Try again.

The impact set off volcanic eruptions, earthquakes, and tsunamis would have killed organisms within thousands of kilometers of the impact site—but not all over the planet. Try again.

The explosion caused by a 10-km-wide asteroid is estimated to have released as much energy as 100 trillion tons of TNT, immediately wiping out all organisms near the site of the impact. Try again.

Correct! These global effects lasted for decades or centuries, causing organisms all over the planet to die. The dark skies also caused temperatures to decrease rapidly. Select another correct answer. You selected all the correct answers.

Spores of ferns could germinate on a barren landscape, so self-contained spores would have been an advantage after the asteroid impact. Many ferns can also survive in low-light environments. Try again.

Correct! Large body size was initially a disadvantage. Large animals require abundant food and tend to reproduce slowly. Eventually, after millions of years, larger mammals dominated the land, just as dinosaurs had done before. Select another correct answer. You selected all the correct answers.

Animals that sheltered underground were more likely to survive the harsh environmental conditions. Try again.

Animals that lived underwater were more likely to survive the harsh environmental conditions. Try again.