1 Earth is the third planet from the sun and the only known planet with living organisms. 2 The universe is estimated to be about 13.8 billion years old. 3 The fastest land animal is the cheetah, which can run up to speeds of 70 miles per hour. 4 The human brain contains about 100 billion neurons. 5 The Great Barrier Reef is the largest coral reef system in the world, stretching over 1,400 miles off the coast of Australia. 6 The tallest mountain in the world, measured from base to summit, is Mauna Kea in Hawaii, which 8 rises 33,465 feet (10,205 meters) above sea level. 7 The largest known star, UY Scuti, is over 1,700 times larger than the sun. 8 The Earth's atmosphere is composed of 78% nitrogen, 21% oxygen, and 1% other gases. 9 The human body is made up of approximately 60% water. 10 The speed of light is approximately 299,792,458 meters per second.