The Changing Earth

1. The Changing Earth Relative aging, fossils, natural disasters

2. Erosion • Rocks breaking down into smaller pieces

3. Runoff • Water that moves over Earth’s surface • Causes sheet erosion • Moves downhill • Forms rills and gullies

4. Rivers • Erosion creates valleys, waterfalls, flood plains, meanders, oxbow lakes • Deposition creates alluvial fans, deltas, add soil to flood plain

5. Groundwater • Underground water • Chemical weathering-water combines with CO2 to form carbonic acid, breaks down limestone • Forms caves, stalactite (roof) and stalagmite (floor)

6. Glaciers • Continental glaciers-covers much of continent, island • Valley glaciers-long, narrow glacier from snow and ice in mountain valley

7. Glaciers • Plucks rocks • Breaks rocks • Drags rocks which scratches bedrock • Deposits sediment when it melts- till, moraine, kettle

8. Waves • Energy comes from wind blown across water’s surface • Break apart rocks on shore • Abrasion-headland, arch, cave • Deposit sediment-beaches, spits, sandbars, barrier beaches

9. Wind • Deflation-wind removes surface materials, Dust Bowl • Abrasion-Polishes rock, little erosion • Deposits-sand dunes, loess-sediment that is finer than sand

10. Loose, weathered material on Earth’s surface in which plants can grow. Soil

11. Rock broken down by weathering • Sediment mixes with materials on surface • Soil horizon-layer of soil that is different in color and texture Soil Formation

12. Topsoil- crumbly, dark soil that is a mixture of humus, clay, and other minerals • Subsoil-Clay, other particles, little humus Soil Layers

13. Humus-formed from organic material • Litter-layer of dead plant leaves • Decomposers-break down organic matter to form humus • Earthworms, and other burrowing animals mix soil Living Organisms in Soil

14. Fertility-ability for plants to grow depend on nutrients in soil • Dust Bowl-loss of topsoil, devastating • Soil conservation by farmers Importance of Soil

15. Fossils • Preserved remains or traces of living things

16. How fossils form • Living things die and are buried in sediments • Sediments harden into rock and preserve shapes of organisms • Sedimentary rock

17. Molds and casts • Most common • Mold-hollow area in sediment in shape of organism • Cast-sold copy of the shape of organism

18. Petrified Fossils • Minerals replace all or part of an organism • Petrified wood

19. Carbon Films • Extremely thin coat of carbon on rock • Carbon from organism left behind in shape of organism

20. Trace Fossils • Provide evidence of activities of organisms • Footprints • Trails • Burrows

21. Preserved Remains • Organism trapped in tar, or amber • Rancho La Brea tar pits • Freezing in Siberia • Protects organism from decay

22. Relative Age of Rocks • Age compared to the age of other rocks • Absolute age-number of years since rock formed

23. Law of Superposition • In horizontal sedimentary rock layers, the oldest layer is at the bottom and each higher layer is younger than the layers below it.

24. Determining Relative Age • Extrusion- lava that hardens on the surface • Always younger than the extrusion below it • Intrusion- Magma that hardens into igneous rock • Always younger than the rock layers around and beneath it • Faults-Break in Earth’s crust • Younger than rock it cuts through • Unconformity- Gap in geological record • Rock layers lost because of erosion

25. Index Fossils • Tell relative ages of the rock layers in which they occur

26. Radioactive Dating • Atoms of one element break down to form atoms of another element • Half-life- time it takes for half of the radioactive atoms to decay • Carbon-14- measure amount of Carbon-14 left in organism to determine absolute age