Earth

Lightning

Lightning is one of the most beautiful displays in nature. It is also one of the most deadly natural phenomena known to man. With bolt temperatures hotter than the surface of the sun and shockwaves beaming out in all directions, lightning is a lesson in physical science and humility. Beyond its powerful beauty, lightning presents science with one of its greatest local mysteries: How does it work? It is common knowledge that lightning is generated in electrically charged storm systems, but the method of cloud charging still remains elusive.

Aurora Borealis

An aurora is a natural light display in the sky predominantly seen in the high latitude (Arctic and Antarctic) regions. Aurorae are caused by cosmic rays, solar wind and magnetospheric plasma interacting with the upper atmosphere (thermosphere/exosphere). Their charged particles, mainly electrons and protons, enter the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent light emissions. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.

Civilization and Human Life

Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to accommodate life. The earliest life on Earth arose at least 3.5 billion years ago. Earth's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99 percent of all species that ever lived on the planet are extinct, Earth is currently home to 14 million species of life, including over 7.3 billion humans who depend upon its biosphere and minerals. Earth's human population is divided among about two hundred sovereign states which interact through diplomacy, conflict, travel, trade and communication media.