Theme 3:Astronomy
Think,pair,share p149
I sometimes think with awe about the possible consequences for life on earth if a comet collided with our planet. I can imagine it hurtling through the atmosphere before it makes its terrible impact on some part of a continent. Scientists do say that a similar incident took place many thousand years ago, and provoked the extinction of many giant animal species, including dinosaurs.
An enormous crater would form, and possibly cause a volcanic eruption which would send a heavy layer of particles and ash high up in the sky to stop the sun rays from reaching the Earth. Our planet would then be in the dark for many years, and consequently the temperatures would drop considerably.
A change in the climate could indeed occur, rainfalls and snowfalls would be frequent, heavy and long lasting, and floods would result from them; the sea level would probably rise, and cause some flat regions of the Earth to be totally immersed.
Another possible consequence of the impact would be a gigantic earthquake which would destroy many inhabited areas and kill a huge number of people. If the impact were near an ocean, a tsunami could develop and flood vast areas of flat land, causing many people to die or become homeless.

Facts in the past have shown that a disaster like an impact of a heavenly body on Earth could destroy life, or at least alter living conditions dramatically. The same could be repeated if another collision occured. This is why scientists are thinking up space programmes to find ways of preventing another accident of this kind.