2. Rock Layers Principle of Superposition – in rock layers that have not been folded or deformed, the oldest rock layers are on the bottom Fossils – preserved remains or evidence of past living organisms

3. Radioactivity Radioactive Decay – process by which one element naturally changes into another parent element  daughter element Half-Life – the time required for half of the amount of a radioactive element to decay by comparing the amount of the parent element to the amount of the daughter element in a substance scientists can calculate the age of the substance

4. 1. If you start with 2000 atoms of a radioactive element, how many atoms of that element will be left after 1 half-life? 2. Carbon-14 has a half-life of 5730 years. If you start with 600 atoms of carbon-14, how many atoms of that element will be left after 17,190 years?

5. Alfred Wegener – proposed that all continents were once part of a supercontinent called Pangaea Continental Drift – suggests that continents are in constant motion on the surface of the Earth

6. Climate sediment deposited by glaciers across the southern continents have similar grooves

7. Fossils fossils of similar organisms have been found on several continents separated by oceans ex. Glossopteris plant

8. Rocks Volcanic Rock – similar types of rock on two different coasts ex. eastern South America and Western Africa Mountain Ranges – different mountain ranges line up and are composed of similar rocks ex. Caledonian Mts. of Europe and Appalachian Mts. of eastern North America

9. Using echo–sounding measurements scientists were able to map the ocean floor Mid-Ocean Ridges long underwater mountain chains running down the middle of the ocean

10. The process by which new oceanic crust forms along a mid-ocean ridge and older oceanic crust moves away from the ridge continents move as the seafloor spreads

11. Mountains form at the mid-ocean ridge or where new crust cools and cracks Abyssal Plain thick layers of sediment far away from the ridge Trenches place where older oceanic crust sinks underneath the continental crust

12. Magnetic Reversals – Earth’s magnetic field reverses itself every few million years Normal Polarity – state in which magnetized objects orient themselves to point north Reversed Polarity – state in which magnetized objects orient themselves to point south

13. Basalt iron-rich rock formed from cooling lava at the mid- ocean ridge orients itself to align with Earth’s polarity shows parallel orientation changes over time