Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

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 Check 

Across: 3. This is often the result when tectonic plates move against each other suddenly 4. A rocky lump held together by frozen gases and ice 5. Name given to the plates on which we live 7. Thick layer of rock beneath the Earth's crust. 9. Molten rock 10. This was thought to be the cause of the extinction of the dinosaurs by some scientists. 11. This was enormous at the beginning of time! 12. Black holes have a very high value for this physical property. 14. Where an oceanic plate can be destroyed. 16. The colour of our Sun when it eventually expands into a 'giant'. 17. The process by which energy is released in a star 18. Rocks undergo this process over millions of years.

Down: 1. On object which orbits a planet. 2. A hole in the Earth's surface where magma is emitted with force. 3. The death of all members of a species. 6. A very large collection of stars, gases and solar systems 8. This is thought to be expanding.... 13. What might happen if the mass of the universe is much larger than we think! 15. Where new tectonic plates are formed