Erosion

Dirt, sand, and rock from the Earth’s surface gets blown, sliced, torn, swallowed and distributed all over the world. What was yesterday’s hill is tomorrow’s flat plain. The planet looks a lot different than it did when it formed four and a half billion years ago. The force of erosion, the slow wearing away of the land, has never ceased.

The tools of erosion are the atmosphere and the oceans. They provide the planet with weather – wind, rain, snow and ice. Weather pelts the surface of the Earth, wearing it down little by little. Rainwater flowing over the ground quickly turns brown as it takes rocks and soil along with it for the ride. As wind barrels against a cliff, tiny particles of the rock get blown away with it. Car exhaust gases fill rain clouds with acid rain, which dissolves away rocks with each falling drop.

Given enough time, the forces of erosion will beat every mountain in the world into smaller and smaller pieces. The effects of erosion are hard to see in a lifetime. The Colorado River is still cutting the Grand Canyon deeper, although no one alive will probably ever notice a significant difference. Since erosion has been happening forever, we can see how erosion has changed the Earth over millions of years. The Earth was so cold over 10,000 years ago that mile-thick sheets of ice called glaciers covered large portions of land. These huge ice flows scraped up rocks in some places, dumping their stony passengers when the glaciers melted.

Erosion can make slow, almost invisible modifications, or sudden, drastic alterations of the landscape. Flash floods re-carve river valleys; mudslides cover roads; sinkholes devour houses. Erosion at a fast rate can spell catastrophe.

The forces of erosion will always be at work, giving the Earth a facelift.

The Big Ideas

• Erosion is the slow wearing away of the Earth's surface.
• Water, wind, ice and chemical reactions cause erosion.

Did You Know That?

• Red clay in very deep ocean water accumulates very slowly — only about 1mm of it piles up over 1,000 years?
• The Grand Canyon represents sediments that piled up for millions of years?
• “Mud” is a scientific term for sediment that is made up of dirt particles smaller than 0.06mm in diameter?

Books of Science!

• “Earth Explained”by Barbara TaylorHenry Holt Company, 1997.
• “Geology Projects for Young Scientists”by Bruce Smith and David McKayFranklin Watts, 1992.