Finish the sentence. The Earth 2.

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Across
  1. 4. Air is made up of many gases, such as _________, which we breath, and carbon dioxide, which is used by plants.
  2. 5. You could sail right around the Earth without seeing land.
  3. 6. About a tenth of the Earth's surface is always covered with ______.
  4. 8. The Earth is surrounded by a layer of ________ about 500 kilometers thick, called the atmosphere.
  5. 10. There are seven big pieces of land called _________________.
  6. 12. Above 12 kilometres of the atmosphere there are no ____________ and the Sun always shines in the daytime.
  7. 13. Only about a ____________ of the Earth's surface is land.
  8. 14. The Poles are the _____________ places on Earth.
  9. 16. The higher you go into the atmosphere, the less air there is and the harder it is to __________ .
  10. 17. We cannot see air but we feel it as _______.
  11. 18. _____________ usually flies higher than the weather, about 13-22 kilometres above the Earth.
Down
  1. 1. Atmosphere stops dangerous _________ from the Sun burning up life on Earth.
  2. 2. Many ______________ are too high and cold for plants and animals to survive there.
  3. 3. Nearly three quarters of the Earth's surface is covered by _______ .
  4. 7. People carry oxygen tanks when they ________ mountains.
  5. 9. The further you travel from the equator, the ___________ it is.
  6. 11. The four __________ are all joined together.
  7. 15. Mount _________ is the highest mountain on Earth, it is 8850 metres high,
  8. 17. All our _________ happens in the first twelve kilometres of the atmosphere.