1) The Amazon rainforest produces more than 20% of the world's oxygen.

2) A single bolt of lightning can heat the surrounding air to temperatures five times hotter than the surface of the sun.

3) The world's largest species of shark, the whale shark, can reach lengths of up to 40 feet (12 meters) and weigh over 20 tons.

4) The Russian Revolution in 1917 resulted in the overthrow of the monarchy and the establishment of a communist government under Vladimir Lenin.