Page 19 - Dinosaur (DK Eyewitness Books)

Impact crater in Mexico's Iridium layer
Yucatán peninsula
CHICXULUB CRATER
A crater 110 miles (180 km) across marks where
the asteroid hit Earth. Few surface traces remain.
Engineers discovered the crater when scouting
sites for oil drilling near Puerto Chicxulub
village, Mexico. Scientists measured the
magnetic field strength across the region
Satellite and found a concentration of magnetic rocks IRIDIUM DEPOSITS
image of at the crater's center, shown in red below. The element iridium is scarce on Earth but
Central This suggests that the impact uplifted strongly plentiful in asteroids. Around the world,
America magnetic rocks from deep beneath Earth's surface. scientists have found a layer of iridium above
A ring of negative readings, in blue, shows the last rock layer with fossil dinosaurs and
where molten surface rock, liquefied by below the first rock layer without dinosaur
the heat of the impact, pooled, fossils. It is believed that this iridium came
became magnetized, from the asteroid that punched out the
and froze. Chicxulub crater. The presence of scraps
of glassy rock that shot up after the impact
and then rained down around the crater
is further evidence of the asteroid impact.
Strongly magnetic
rocks at center
TINY VICTIMS
Soft, white chalk is a pure variety
of limestone formed from the shells
of trillions of tiny organisms called
coccolithophores. Late in the Cretaceous
Map of the Period, their remains formed thick chalk
magnetic field in layers beneath the sea. Such layers now
the crater region
form England’s chalk sea cliffs. Almost
all coccolithophores mysteriously
Ring of magnetism disappeared around the same
reveals the crater's shape
time as the dinosaurs.
Massive Fragment of chalk
beak
DEATH IN THE OCEAN
Other organisms, such as
ammonites, also became
extinct around the same OUTLASTING THE CATASTROPHE
time as the dinosaurs. This flightless bird belonged to one of the groups
Ammonites were sea of animal that survived the mass extinction, which
creatures related to squid, brought the Cretaceous Period to an end. Gastornis
and their numbers had already (“Gaston’s bird”) had a powerful kick, a massive
begun to decline late in the Cretaceous beak, and stood taller than a man. For a time, it
Period due to a loss of habitat. Undersea seemed that such birds might fill the gap left by
volcanic activity in the mid-Cretaceous the predatory dinosaurs, but birds like this
caused changes in the seafloor. The sea eventually died out as well.
level rose and the ocean spilled over low-lying
lands, creating shallow seas that were ideal habitat
for ammonites and a range of reptiles and other
organisms. When the seas retreated later in the
Cretaceous, the ammonites and other wildlife
lost their homes.
Stumpy wings

Tidal waves rippling
over the ocean

Hooflike claws

MAMMAL SURVIVORS
Ten million years after most dinosaurs died out, Phenacodus,
a furry plant-eater with hooflike claws and grinding cheek
teeth, roamed the woodlands of North America and Europe.
Mammals far larger than this sheep-sized animal also
began to appear by this time, and they survived because
there were no large theropods to prey on them.

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