Khan Academy
Khan Academy: Timekeeping
Why do we need calendars and clocks? To survive in this complex society, you need to track what others are doing and when they're doing it. You also need to know what's happening in the natural world. This article discusses how/why...
CK-12 Foundation
Ck 12: Life Science: 4.4 Fossils
Understand fossils and the fossil record as it relates to Earth's history.
US Geological Survey
U.s. Geological Survey: Geologic Time
A discussion of geologic time, how scientists use the concept, and how they have determined its span.