How much of Earth's surface is covered by water? How do the northern lights get their colors? Planet Earth has been home to mankind for hundreds of thousands of years and while scientists have learned a lot about it, they're still unraveling many of its mysteries. B is for Blue Planet: An Earth Science Alphabet explains what we do know about our planet and what more we have to learn. Examine Earth's diverse ecosystems (deserts), discover geological wonders (karst caves), learn about weather phenomena (hurricanes), and much more.