Geological Evolution. Mrs. Pittaluga 8 th Grade Science

Transcription

1 Geological Evolution Mrs. Pittaluga 8 th Grade Science

2 The Birth of a Science James Hutton Father of Modern Geology Helped developed theories related to geologic time, otherwise known as deep time. Principle of Uniformitarianism Hutton said that the history of the earth can be determined by understanding the processes that work in the present day, such as erosion and sedimentation.

3 How Age is Determined Relative Dating Allows a researcher to determine if a sample is older or younger than a reference sample. Geologists use methods such as the law of superposition, intrusions, and unconformities to determine relative age. Absolute Dating Allows a researcher to determine a more accurate age of a sample in years. Radioactive dating and tree rings are forms of absolute dating.

4 Principles of Geology Science of stratigraphy branch of geology that studies rock layers for relative dating. A series of laws formulated by Nicholas Steno in the late 1600s The Law of Original Horizontality The Law of Superposition The Law of Cross-Cutting Relationships

5 Original Horizontality States that sediments are deposited in horizontal layers that are parallel to the surface on which they were deposited.

6 Superposition In a sequence of sedimentary rock layers, the oldest layer is at the bottom and the youngest layer is at the top.

7 Cross-Cutting Relationships Any sediment or lava flow that is cut by a fault, another igneous body, or an erosional surface is older than the crosscutting feature.

8 Sedimentary rocks in a quarry near Decorah, IA demonstrating the law of original horizontality AND the law of superposition. These rock layers have remained in the same orientation since the sediment was first deposited some 450 million years ago. Darker shale-rich layers near the base are older than the lighter carbonate layers overlying them.

9 The Rock Sequence Which is the proper sequence of the illustrated rock layers from oldest to youngest? a) F E D C B A b) A B C D E F c) F E C D B A d) D E F C B A

10 Other Geologic Features Extrusion Occurs when magma flows onto the surface and then hardens, often into basalt. Intrusion Occurs when magma pushes into bodies of rocks, then hardens in a mass of igneous rock Faults A break in Earth s crust Unconformities Shows where some rock layers may have been lost due to erosion or weathering.

11 Extrusions Intrusions

12 Faults Unconformities

13 Weathering Chemical Weathering The process that breaks down rock through chemical changes. Examples of chemical weathering include: water dissolving certain minerals in rock, exposure to oxygen from the air reacting with chemicals in the rock, exposure to carbon dioxide from the air reacting with chemicals in the rock, or acids from plants or acid rain reacting with the chemicals in the rock.

14 Chemical Weathering

15 Weathering Mechanical Weathering Weathering that occurs when rock is physically broken down into smaller pieces. This could include: trees growing into a rock and splitting it, ice freezing in cracks and causing the cracks to expand, abrasion from smaller particles and water, pressure being applied on top of or underneath the rock.

16 Mechanical Weathering

17 Radioactive Dating During radioactive decay, the atoms of one element break down to form atoms of another element. The rate of decay is the element s half-life, or the time it takes for half of the radioactive element to break down. Parent isotope is the main element; The daughter isotope is what the parent decays into. Isotopes are different versions of the same element Carbon-14 (Decays to Nitrogen-14) Most often used for dating plants and animals Has a half-life of 5,730 years Uranium-235 (Decays to Lead-207) Often used for dating rocks since it decays into lead Has a half-life of 713 million years

18 Potassium-40 Decays to Argon-40 Has a half-life of 1.25 billion years

19 The Birth of a Theory Alfred Wegener proposed the continental drift theory in the early 20 th century Observed the puzzle-like shape of the continents. Learned of fossils of similar species being found on continents now separated by great distances. Climate studies revealed that glaciers covered large areas of land now separated by great distances. Theory was later disproved because he couldn t adequately explain HOW the plates moved. Discarded until after World War II when naval ships created detailed maps of the sea floor and the midocean ridge was discovered. Today it is known as the Theory of Plate Tectonics.

20 Plate Tectonics About 200 million years ago, there was a supercontinent that Wegener called Pangaea (meaning all the land in Greek). Started to break up about 130 mya into two large continents that were called Laurasia and Gondwanaland. Fossil record supports this theory Pangaea Animation Around 65 mya the continents as we know them today began to take shape.

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