Questão 162021Inglês
(AFA - 2021)
The End of life on Earth
It weighted about 10,000 tons, entered the
atmosphere at a speed of 64,000 km/h and exploded
over a city with a blast of 500 kilotons. But on 15
February 2013, we were lucky. The meteorite that
5showered pieces of rock over Chelyabinsk, Russia, was
relatively small, at only about 17 metres wide. Although
many people were injured by falling glass, the damage
was nothing compared to what had happened in Siberia
neraly one hundred years ago, when a relatively small
10object (approximately 50 metres in diameter) exploded in
mid-air over a forest region, flattening about 80 million
trees. If it had exploded over a city such as Moscow or
London, millions of people would have been killed.
By a strange coincidence, the same day that the
15meteorite terrified the people of Chelyabinsk, another
50m-wide asteroid passed relatively close to Earth.
Scientists were expecting that visit and know that the
asteroid will return to fly close by us in 2046, but the
Russian meteorite earlier in the day had been too small
20for anyone to spot.
Most scientists agree that comets and asteroids
pose the biggest natural threat to human existence. It
was probably a large asteroid or comet collinding with
Earth which wiped out the dinosaurs about 65 million
25years ago. An enormous object, 10 to 16 km in diameter,
struck the Yucatan region in Mexico with the force of 100
megatons. That is the equivalent of one Hiroshima bomb
for every peerson alive on Earth today.
Many scientists, including the late Stephen
30Hawking, say that any comet or asteroid greater than
20km in diameter that hits Earth will result in the
complete destruction of complex life, including all
animals and most plants. As we have seen even a much
smaller asteroid can cause great damage.
35The Earth has been kept fairly safe for the last 65
million years by good fortune and the massive
gravitational field of the planet Jupiter. Our cosmic
guardian, with its stable circular orbit far from the sun,
sweeps up and scatters away most of the dangerous
40comets and asteroids which might cross Earths orbit.
After the Chelyabinsk meteorite, scientists are now
monitoring potential hazards even more carefully but, as
far as they know, there is no danger in the foreseeable
future.
45Types of space rocks
Comet - a ball of rock and ice that sends out a
tail of gas and dust behind it. Bright comets only appear
in our visible night sky about once every ten years.
Asteroid - a rock a few feet to several kms in
50diameter. Unlike comets, asteroids have no tail. Most
are to small to cause any damage and burn up in the
atmosphere.
Meteoroid - part of an asteroid or comet.
Meteorite - what a meteoroid is called when it
55hits Earth.
Taken from: http://learningenglishteens.britishcouncil.org - Access on 29/06/2020
According to the text
