Newsademic British English edition 260

in o s a u r
 
extin c tio n
 
e x p l a in e d
?
It’s known that the dinosaurs died 
out, or became extinct, 66 million 
years ago. In recent years there have 
been arguments about what caused 
this extinction. Many scientists be­
lieve the dinosaurs disappeared after 
a large asteroid hit the Earth. Others 
suspect that enormous volcanic erup­
tions are the more likely reason.
Now, a group o f researchers from 
the USA have proposed that these 
two events were connected. They 
believe the asteroid impact greatly 
increased the size o f the eruptions.
If this is true, the asteroid caused the 
death o f some dinosaurs. Those that 
survived were then killed off by the 
volcanic eruptions, which poisoned 
the atmosphere.
The idea that an asteroid or comet 
killed all the dinosaurs was first 
thought o f in 1980. Later, scientists 
discovered that a large asteroid, 
at least ten kilometres (6.2 miles) 
across, did hit the Earth around 66 
million years ago. It crashed into the 
planet at a place called Chicxulub. 
This small town is on the north coast 
o f the Yucatan Peninsula, in Mexico.
An asteroid impact o f this size 
would have set off huge fires, earth­
quakes, landslides, and giant waves 
(or tsunamis). Dust, ash and dirt 
must have been thrown high into the 
air. This may have spread around the 
Earth and blocked out the Sun. So 
temperatures would have become 
much colder. Plants and trees may 
have stopped growing. If this hap­
pened, plant-eating dinosaurs and 
those that preyed, or fed, on them 
would have starved.
The period during which the last 
dinosaurs lived is known as the Cre­
taceous. The era after they died out 
used to be called the Tertiary. There­
fore the boundary between the Cre­
taceous and the Tertiary marks the 
dinosaurs’ extinction. This is known 
as the K-T boundary. (The K comes 
from the word for Cretaceous in Ger­
man.) The die-off o f the dinosaurs is

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