Question 167
MediumOriginal questionAbout 4.6 billion years ago, there was no Sun and no Earth, only a thin, cloud of dust and gas, part of a much larger cloud called a nebula.
At some point this cloud . It may have been pushed by the shock wave of a nearby star exploding. As it fell in on itself, it formed a spinning disk of material, and at its centre the pressure grew so great that hydrogen atoms began to into helium, giving off a amount of energy. The Sun was born.
The young Sun gathered up more than ninety-nine per cent of all the material in the disk. What was left began to together under gravity. Small objects crashed into bigger ones, forming bigger objects still, until some were large enough to become round: the planets and the dwarf planets.
Where each planet formed depended on heat. Close to the Sun, only rock could survive, so the rocky planets, like the Earth, formed there. Farther out, gas and ice collected into the giant planets.
Not everything became a planet. The asteroids are pieces that never quite came together, and the icy comets far out in the solar system have hardly changed since those early days. By studying them, scientists piece together this long story.
What does "The Sun was born" mark in the passage?
Show the answer and explanation
Correct answer: A
Explanation
The sentence comes straight after hydrogen atoms "began to fuse into helium, giving off a tremendous amount of energy".
That burst of energy is what turned the centre of the disk into the Sun.
Worth noting
The planets form later, in the next paragraph.
- Concept
- Following the order of events
- Typical timeTypical
- 45 s
- Your timeYours
- —
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