geology

Physics & Space

Earth History & Geology

• Geological Time OverviewEarth history is 4.54 billion years long, but the part most familiar from fossils occupies only a thin recent slice. The Phanerozoic Eon — abundant visible animal life — begins only 538.8 million years ago, roughly the last 12% of Earth's history.
• How We Know the Age of EarthEarth is about 4.54 billion years old. The important part is not memorizing the number; it is understanding why we trust it.
• Pangaea and Continental DriftPangaea was the supercontinent that assembled by the late Paleozoic and contained most of Earth's continental land. It began breaking apart roughly 200 million years ago, eventually producing today's Atlantic Ocean and continental arrangement.
• Radiometric DatingRadiometric dating turns radioactive decay into a clock. If a parent isotope decays with constant decay constant \(\lambda\), then