Planet Earth

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Across
  1. 4. Driest non-polar desert on Earth (7)
  2. 6. Flat, elevated landform that rises sharply above surrounding area (7)
  3. 9. Huge ocean wave caused by underwater disturbance (7)
  4. 14. Atmospheric layer that protects Earth from UV radiation (5)
  5. 15. Layer between Earth's crust and core (6)
  6. 17. Process of recycling elements between Earth's systems (6,5)
  7. 19. Vast region in Russia known for its harsh climate (7)
  8. 22. When the Moon passes between the Earth and the Sun, blocking sunlight (7)
  9. 24. Period of long-term reduction in Earth's temperature (3,3)
  10. 26. Large, slow-moving mass of ice (7)
  11. 27. Line that divides Northern and Southern Hemispheres (7)
  12. 28. Supercontinent that existed millions of years ago (7)
  13. 29. Molten rock beneath Earth’s surface (5)
  14. 30. Explorer who travelled to Asia in the 13th century (5,4)
  15. 31. Type of plates that move and cause earthquakes (8)
  16. 34. Outermost layer of Earth (5)
  17. 38. Global sum of all ecosystems on Earth (9)
  18. 39. Arid region with very little rainfall (6)
Down
  1. 1. Grassland ecosystem with scattered trees, found in Africa (7)
  2. 2. Largest ocean on Earth (7)
  3. 3. A hot spring that periodically erupts with water and steam (6)
  4. 5. Longest continental mountain range (5)
  5. 7. Layer of gases surrounding Earth (10)
  6. 8. Deep valley, often formed by a river (6)
  7. 10. Spectacular Nordic natural light display (6,8)
  8. 11. Northernmost and southernmost points on Earth (5)
  9. 12. Body of water with the highest salt content (4,3)
  10. 13. Rupture in the Earth’s crust that emits molten lava (7)
  11. 16. Sudden shaking of the ground (10)
  12. 18. Longest river in the world (4)
  13. 20. Layers of rock or soil with distinct characteristics (6)
  14. 21. most populated country in the world (5)
  15. 23. Mountain range containing the highest peak on Earth (9)
  16. 25. Largest rainforest in the world (6)
  17. 26. Force that keeps us anchored to Earth's surface (7)
  18. 32. Cold, treeless region found near the Arctic Circle (6)
  19. 33. Process by which wind and water wear away rocks and soil (7)
  20. 35. Lines that circle the globe, known for warm temperatures (7)
  21. 36. Largest hot desert on Earth (6)
  22. 37. Innermost layer of Earth (4)