Basics of Geology
By Andrew Alden, About.com Guide to Geology
There are many ways that lead to geology, whether it's the rocks along the road, the threat of climate change or the sights from your vacation. Here are the major avenues.
- Geologic Time
- Evolution
- Parts of the Earth
- Plate Tectonics
- Geology of Other Planets
- Resources for Learning and Teaching
Rocks
Rocks are what the Earth is made of. The first thing geologists learn is how to observe, describe and classify rocks.
- How to Look at a Rock
- What Is a Rock?
- Picture Gallery of Rock Types
- Quick Rock Identification
- Introducing Igneous Rocks
- Pictures of Igneous Rock Types
- Sedimentary Rock Basics
- Pictures of Sedimentary Rock Types
- Metamorphic Rocks in a Nutshell
- Pictures of Metamorphic Rock Types
Minerals and Gemstones
Minerals are the ingredients of rocks. Just a few important minerals account for the majority of rocks and for the soil, mud and sand of the Earth's surface. Many of the most beautiful minerals are treasured as gemstones.
- What Is a Mineral?
- Identify Minerals in 10 Steps
- The Mohs Scale of Mineral Hardness
- Picture Gallery of Minerals
- The 9 Common Rock-Forming Minerals
- Minerals of the Earth's Surface
- Gemstones and their Mineral Names
- Optical Effects in Gemstones
Earth Resources
Many rocks and minerals are important for civilization. They are products we take from the Earth. Learn more about their geology.
- Stone in Industry
- Stone Tools Ancient and Modern
- Geothermal Energy
- Petroleum - Oil and Gas
- Coal Basics
- About Salt
- Iron and Iron Minerals
- Uranium Geology
- About Mercury Metal
- Conflict Diamonds and Other Minerals
- Cement and Concrete
- Brick: An Artificial Rock
- Phosphate in a Nutshell
- Water and Hydrology
Geologic Hazards
Hazards are ordinary geologic processes that interfere with human life. Here are introductions to the major geologic hazards. For news and background about current hazard events, see the Quakes & Other Events tab.
Landforms
The hills, valleys and other features of a landscape are signs of the area's underlying structure and clues to its history.
- Landform Picture Gallery
- What Builds Mountains?
- Mountain Picture Gallery
- Glaciers and Glacial Landforms
- Dry Lake Beds and Salt Flats
Fossils
Fossils are precious gifts from the geologic past: signs and remains of ancient living things that help explain how life has coexisted with Earth. Fossils are an important line of evidence showing how life has evolved since its still-mysterious beginnings.
Geologic Time
All of human history is the briefest moment at the end of four billion years of geologic time. How do geologists measure and order the milestones in Earth's long history?
- Geologic Eons and Eras, the Large Scale
- Precambrian Time Scale, 4500 to 542 Million Years Ago
- Phanerozoic Time Scale, 542 Million Years Ago to Present
- How We Map Deep Time
- Paleozoic Era Time Scale (542 to 251 Million Years Ago)
- Mesozoic Era Time Scale (251 to 66 Million Years Ago)
- Cenozoic Era Time Scale (66 Million Years Ago to Present)
- How We Measure Deep Time
Evolution
The consistent parade of fossil species through geologic time shows that life has been evolving since its remote beginning. Modern genetics tells the same story. Geology also shows that species have gone extinct.
- Evolution in a Nutshell
- Extinction, the Destiny of Species
- Recovering Ancient DNA
- "Intelligent Design" Analyzed
Parts of the Earth
Beneath the stony crust lie the rocky mantle and, at Earth's heart, the iron core. All are areas of active research and competing theories.
Plate Tectonics
Plate tectonics is the first theory that explains the mechanics of the Earth's surface in depth, in detail and in a scientifically fruitful way.
- The World's 30 Largest Plates
- How Volcanism Reflects Plate Tectonics
- How Hotspots Reflect Plate Tectonics
Geology of Other Planets
The space program has revolutionized geology by giving us other examples of planets besides our own: they include Mercury, Venus, the Moon, Mars, the asteroids and the larger planetary satellites.
Resources for Learning and Teaching
Charles Darwin once wrote, "Geology is a capital science to begin, as it requires nothing but a little reading, thinking, and hammering." Whether you study for pleasure at home or stand in a classroom and teach, I can help.
