Weathering, erosion, deposition and soil

Weathering is the breakdown of rocks and minerals on the earth's surface. Many things cause this to happen. There are two types of weathering: Mechanical (physical) Chemical

What is mechanical weathering? It is when rocks break down into smaller pieces because of some physical force. The rock does not change chemically, it just gets smaller!

Photo by A. Criminger Freezing and thawing is breaking these rocks apart!

Photo by A. Criminger Roots are breaking these rocks apart.

Photo by A. Criminger Ice is breaking these rocks apart

What is chemical weathering? Chemical weathering occurs when rocks are broken down by a chemical reaction. This can happen by water, oxygen, acid rain, and even living things.

Photo by A. Criminger This rock is being broken down by the chemicals in the roots of the lichen growing on the rock.

Photo by A. Criminger Sometimes rocks are not the only things that get chemically weathered!

What happens next? Erosion now takes place. Erosion is the moving of sediment (broken rocks and plant material) to a new location. So what is the difference between weathering and erosion?

Erosion can occur by water! http://www.geography.wisc.edu/department/overview.htm What is the evidence that sediment is being moved from one place to another?

Erosion can occur by wind! Copyright © Marli Miller, University of Oregon http://www.csiro.au/files/mediaRelease/mr2000/dust.htm www.wilderness.org.au Wind moved the sand into a dune.

Erosion can occur by ice! A glacier is a “river” of ice that slowly moves downhill. As it travels, it breaks off rock and carries it to a new location – EROSION! Copyright © Marli Miller, University of Oregon Rocks moved by a glacier. This is glacier deposition. What does the word “deposit” mean? Copyright © Bruce Molnia, Terra Photographics

Courtesy National Oceanic and Atmospheric Administration Glaciers form U shaped valleys. After the glacier melts - Copyright © Larry Fellows

After sediment has been moved it will be dropped off someplace. This is called deposition! Copyright © Marli Miller, University of Oregon Notice the sediment deposited by the river and the wind.

What is soil and why is it important?

Much of the life on earth depends on soil. Soil is made of weathered rock and decayed parts of plants and animals. Soil provides the nutrients needed by most plants to grow. http://tiee.ecoed.net Photo: A. Criminger

How does soil form? The first step is for bedrock to be broken down by weathering . This weathering can happen by wind, water, or changes in temperature. Wind Water Temperature Copyright © Bruce Molnia, Terra Photographics Copyright © Marli Miller, University of Oregon Photo: A Criminger

Second step to soil formation: Organisms such as bacteria and fungi begin to grow in the broken down bedrock . http://waterandlife.org/MicroBiota.htm Soil bacteria (Image: USDA) Soil fungi These organisms live and die providing the soil with nutrients that other plants need to grow.

Soil is a mixture of Rock particles Minerals Decayed plant and animal material Air Water

Rock particles

Minerals

Decayed plant and animal material

Air

Water

When we dig into the earth, we can see that the soil changes with depth. This is called a soil profile ! http://epod.usra.edu

North Georgia soil profile http://www.ga.nrcs.usda.gov/technical/soils/red.html Not all Georgia soils are red, but many of them are. The State is well known for its abundance of "Georgia Red Clay". People often ask why the soils are red. The red color that is so evident in Georgia soils is due primarily to iron oxides. Georgia soil is red because the iron in it has bonded with oxygen forming molecules of “rust.”

Why is soil important? Without soil, life on earth would be very different. Imagine no plants that grew in soil. No animals that grazed on plants. Where would we get our food? What would we eat? What do you think?

Without soil, life on earth would be very different.

Imagine no plants that grew in soil.

No animals that grazed on plants.

Where would we get our food?

What would we eat?

What do you think?