How Fossils Map the Past     Only a tiny fraction of the organisms that have lived during the geologic past have been preserved as fossils.Normally the remains of an ani...

Parental Care by Frogs Only an estimated 10 percent of anuran (frog and toad) species provide any kind of parental care. But within this 10 percent there is very great diversity ...

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 ...

重复时间 2024-06-18 2024-09-28 2025-02-22 Equestrian Portraits in the Eighteenth and Nineteenth Centuries     It was common for European rulers from the eighteenth ...

The Moon's Origin   One of the earliest scientific theories about the Moon's origin postulated that Earth and its moon formed out of a dust cloud alongside one another, much a...

The Origin of Mars's Moons     Mars has two tiny moons, Phobos and Deimos. The orbits of both these satellites are nearly circular and close to the planet: Phobos orbits...

Why Did Agriculture Arise   Sometime around 10,000 years ago, some hunter-gatherers took up agriculture. Though the advantages may seem obvious, there are also disadvantages: ...