Jazz   Jazz music, an art form original to the United States, originated in the southern city of New Orleans at the turn of the twentieth century. It combined the elements of ...

Erratics and Drift   In the nineteenth century, scientists theorized that glaciers (ice sheets) covered much of Earth's surface during an ancient very cold period known as the...

Mars's Disappearing Atmosphere   For about the first billion years of its life, Mars was probably a watery planet. There are signs of past water in surface features, such as d...

The Early Iron Age     During the Bronze Age (roughly 3300-1200 B.C.E. in the Middle East), civilizations were limited in their use of iron. Most iron occurred not in ...