Crossword Trouble

123456789101112
Across
  1. 3. If a person studies _____ then he studies DNA.
  2. 5. ______ change isn't always caused by humans.
  3. 7. Garbage _______ the sea and kills animals.
  4. 8. _______ means different things.
  5. 9. _______ means when a species no longer exists.
  6. 10. ______ gases pollute the air.
  7. 11. ______ is plants, living forms and all kinds of things natural.
  8. 12. Global warming can ______ the ozone layer.
Down
  1. 1. ______ that grow give us more oxygen in the world.
  2. 2. _____ means life.
  3. 4. Humans are ______ every day, every second.
  4. 6. The place that surrounds you is called the _______.