Weathering, Erosion, Deposition and Geologic Time Scale

1. Weathering, Erosion, Deposition and Geologic Time Scale

2. Weathering • Weathering is the process that breaks down rock and other substances at the Earth’s surface. • Heat, cold, water, and ice all contribute to weathering. • Repeated freezing and thawing for example can crack rock apart into smaller pieces.

3. Pictures of Weathering

4. Erosion • The forces of weathering breaks rocks into smaller and smaller pieces. Then the forces of erosion carry the pieces away. • Erosion is the movement of rock particles by wind, water, ice, or gravity. • Weathering and Erosion work together to wear down and carry away the rocks at the Earth’s surface.

5. Weathering and Erosion • Weathering and erosion together can form things like: • Caves • Canyons • Valleys • Arches • Steep Cliffside's • Remember this is primarily caused by wind, water, and gravity.

6. Pictures of Erosion

7. Erosion by Rivers • Through erosion a river creates valleys, waterfalls, flood plains, and meanders (loop like bend in a river) • Grand Canyon Formation

8. Deposition • Both weathering and erosion produce sediment. • Deposition is the process in which these new rock sediments are laid down in new locations. • So collectively erosion and weathering break down rock and deposition relocates the new sediments into layered rocks or sedimentary rock.

9. 2 Types of Weathering • Mechanical Weathering occurs when rock is physically broken into smaller pieces. • Mechanical weathering breaks rocks into pieces by freezing and thawing, growth of plants, actions of animals, and abrasion. • Abrasion is the grinding away of rock by rock particles carried by water, ice, wind, or gravity. • Mechanical Weathering works slowly but over long periods of time it wears down whole Mountains • Mechanical Weathering in Ireland

10. 2 Types of Weathering • Chemical Weathering is the process that breaks down rock through chemical changes. • The agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain. • Chemical Weathering produces rock particles that have a different mineral makeup from the rock they came from.

11. Chemical Weathering • Over time many rocks will dissolve in water. • Rock that contains iron rust through the process of oxidation. • Carbon Dioxide becomes dissolved in rainwater and in water that sinks through air pockets in the soil. The result is a weak acid called carbonic acid which can easily weather marble and limestone. • Burning coal, oil, and gas can pollute the air with sulfur, carbon, and nitrogen compounds. These compounds react chemically with the water vapor in clouds to form acids.

12. Rate of Weathering • The rate of weathering usually depends on the type of rock and the local climate. • Chemical weathering occurs faster at higher temperatures. Usually were the climate is hot and wet.

13. Gravity’s Effect on Earth’s Surface • Gravity is the force that moves rock and other materials downhill. • Mass movement of rocks or sediments can be fast or slow. • The different type of mass movements caused by gravity include landslides, mudslides, slump, and creep.

14. Landslides Caused By Gravity • Most destructive kind of mass movement is a landslide. • Landslides occur when rock and soil slide quickly down a steep slope. • Landslides are common when road builders have cut highways through hills or mountains. • Hawaii Weathering and Erosion

15. Mudflows Caused By Gravity • Mudflow is the rapid downhill movement of a mixture of water, rock, and soil. • Mudflows often occur after heavy rain • The amount of water in a mudflow can be as high as 60%.

16. Slumps Caused by Gravity • Slumps occur when a mass of rock and soil suddenly slips down a slope. • Unlike a landslide the material in a slump moves down in one large mass. • Caused by gravity’s pressure over time.

17. Creeps Caused by Gravity • Creep is the very slow downhill movement of rock and soil. • Creep often results from the freezing and thawing of water in cracked layers of rock beneath the soil.

18. Geologic Time Scale • Scientists use the Law of Superposition to determine the relative ages of sedimentary rock layers. • According to the Law of Superposition, in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below.

19. Extrusions and Intrustions • Lava that hardens on the surface is known as an extrusion. • The rock layers below and around an extrusion are always older then the extrusion. • Beneath the surface, magma may push into bodies of rock. There, the magma cools and hardens into a mass of igneous rock called an intrusion. • An intrusion is always younger then the rock around it and below it.

20. Unconformity in Rock Layers • An unconformity is a gap in the geologic record. • An unconformity shows where some rock layers have been lost due to erosion.

21. Carbon Dating of Rocks • Most elements are stable, they do not change under normal conditions. • Some elements exists in forms that are unstable. Over time these elements break down or decay, by releasing particles and energy in a process called radioactive decay.

22. Carbon Dating of Rocks • The rate of decay of each radioactive element is constant. • Elements have a half life’s this is what it takes for half of the radioactive atoms to decay. • Geologists use radioactive dating to determine the absolute age of rocks. • Geologists compare how much of the element is left compared to how much is normally there under normal conditions. Since they know the half-life of elements they can then deduce the actual age of the rocks.

23. Carbon 14 Dating • Most particles or elements of carbon have an atomic mass of 12.011 there are some isotopes of carbon that have a larger atomic mass, for example carbon 14, which is found in most organic material. • We us the isotope carbon 14 to tell us the relative age of rocks, if they contain organic material. • For example we know the half life of carbon 14 is 5,730 years. So if we find a rock that has carbon and it’s atomic mass is approximately 7 then 5,730 years have passed since it originally formed.

24. SOIL, DIRT, and PLANTS OH MY!!! • Soil is a mixture of decayed organic material and minerals. • The organic material comes from dead plants, such as last years leaves. • The minerals come from rocks underground typically known as bedrock.

25. So How Old is the Earth? • Geologists believe that the Earth is roughly 4.6 BILLION YEARS OLD!!!!!!!

26. Folding of Earth’s Materials • Have you ever skidded on a rug that wrinkled up as your feet pushed it across the floor? • Rock stressed by compression may bend slowly without breaking creating folds. • Folding can cause the youngest rock to not always appear on the top of rock formations.

27. It’s Your FAULT!!!!!! • Mountain building can be caused by folds and faults. • This process takes millions of years!!! • Faults usually occur along plate boundaries where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks. • Faults can also cause layering where the youngest rock is not always on top.