April 21, 2021

Rainbow What Colors Are Rainbows: A rainbow is a multicolored arc made of light-striking water droplets. The most familiar type of rainbow, including this one in southern Chile, is produced when sunlight strikes raindrops in front of a…

Ocean For upon |The ocean is a huge body of salt water that covers about 71 percent of the Earth’s surface. The planet has one global ocean, though oceanographers and the nations of the world have divided it into distinct geographic…

Antarctica The Antarctic is the only continent with no permanent human habitation. There are, however, permanent human settlements, where scientists and support staff live for part of the year on a rotating basis. Dry Valleys…

Natural Selection For upon |Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways. This…

Earth Atmosphere For upon |Earth’s atmosphere stretches from the surface of the planet up to as far as 10,000 kilometers (6,214 miles) above. After that, the atmosphere blends into space. Not all scientists agree on where the actual upper…

Earth's Interior For upon |Earth’s core is the very hot, very dense center of our planet. The ball-shaped core lies beneath the cool, brittle crust and the mostly solid mantle. Click through the gallery to learn more about the core and…

Jul 16, 1054, CE: Great Schism For upon |On July 16, 1054, the Patriarch of Constantinople Michael Cerularius was excommunicated, starting the “Great Schism” that created the two largest denominations in Christianity—the Roman Catholic and…

Symbiosis: The Art of Living Together For upon |Symbiotic relationship is a term describing any relationship or interaction between two dissimilar organisms. The specific kind of symbiosis depends on whether either or both organisms…

For upon |A biome is a large community of vegetation and wildlife adapted to a specific climate. The five major types of biomes are aquatic, grassland, forest, desert, and tundra. Saguaro Cacti Large Saguaro cacti (Carnegiea gigantea) pop…

Water Table For upon |The water table is the boundary between the unsaturated zone and the saturated zone underground. groundwater fills any spaces between sediments and within the rock. Fresh Water Spring Iran A freshwater spring in the…