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14 Cards in this Set
- Front
- Back
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How did the Universe begin? |
Scientists believe that the universe began in a hot 'big bang' about 14,000 million years ago.
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What is the 'Big Bang' theory? |
The theory states that about 13,700 million years ago all the matter in the universe was concentrated into a single incredibly tiny point.
This began to enlarge rapidly in a hot explosion, and it is still expanding today. |
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What was the first element to form? |
Hydrogen |
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How were the elements formed? |
All 92 elements on Earth, including those that make up our bodies, were formed at the heart of a star.
Small stars like our Sun produce the lighter atoms through fusion reactions. Larger stars with heavier cores make the heavier elements up to iron. The rest are forged by exploding supernovae or the death of largest stars. |
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How were the planets formed? |
Planets form out of a collapsing cloud of dust and gas within a larger cloud called a nebula. The centre of the cloud gets more and more compressed and becomes a new star. The remaining gas and dust rotates and forms a disc around the star. Over time, this material clumps together to form planets, moons, asteroids and comets. |
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What influence caused the first stars to form? |
Gravity. |
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Why were early stars almost purely hydrogen? |
After the Big Bang, the only element around was hydrogen. |
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Where did the carbon that we depend on for life come from? |
Other stars that fused together lighter elements exploded, sending particles of heavier elements off into space. |
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Describe what will happen inside the Sun towards the end of its life that will create elements heavier than hydrogen. |
Nuclear fusion of hydrogen forms helium and as the hydrogen fuel is used up, helium itself will start to fuse to form heavier elements as far as iron. |
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Describe what must be happening to the percentage of hydrogen in the universe. Explain why you think this. |
The percentage of hydrogen in the universe must be decreasing as it is fused into heavier elements in the hearts of stars. Fusion is a one-way process as there is no known natural process that makes heavier elements split into lighter ones except for fission, which only affects a few heavy elements. |
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(a) Use the periodic table to list the elements that are formed by normal stars. (b) What is the name of the lightest element that cannot be formed by fusion in a normal star? |
(a) He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si,Ti, V, Cr, Mn, Fe. (b) Cobalt. |
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Explain why some scientists think that many of the early stars may have been more massive than our Sun. |
The building material for stars (hydrogen) would have been more dense in the early universe. Also, to form the heavier elements such as gold or uranium, there must have been many supernovas. |
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The early stars formed from clouds of hydrogen. Explain why these early stars could not have had planets, and where the different atoms that make up our Solar System came from. Include examples of the formation of elements, including iron and gold. |
Before the early stars formed, the vast majority of atoms were hydrogen, with small amounts of helium and lithium.
There were no heavier elements so no planets could form. The early stars fused together hydrogen to form heavier elements asfar up the periodic table as iron. Some of the early stars were very large and eventually exploded in a supernova. During this explosion, elements heavier than iron, such as gold, were formed. The atoms from the early stars were spread across space when the stars died. Later the atoms became parts of new star systems including our own Solar System. |
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What are the key points to remember? |
Stars form when gas and dust condense under gravity and eventually becoming so hot that fusion starts.
Fusion creates the elements heavier than lithium. Elements that are heavier than iron are formed in supernovas. Planets are formed by the heavier elements in a dust cloud gathering together in a disc and eventually forming bigger and bigger lumps. |
