Think ; Pair ; Share 
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.