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pg. D 82 |
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People once believed Earth was only several thousand years old. Original Horizontality - Idea that explains that sedimentary rocks form in horizontal layers. Superposition- Idea that the bottom layer in a series of rock layers is older than the layers above it. The Relative Age of a rock is determined by comparing it with other rocks. Geologic Column A listing of Earth's rock layers in order from oldest to youngest. Radioactivity- Used to determine the accurate age of a rock. ---------------- Fossil- The remains, trace, or imprint of a living thing preserved in Earth's crust. Hard parts of plants and small animals such as teeth and bones, shells, seeds, pollen, grains, and wooden stems, are often preserved as fossils. Teeth and bones are the most likley parts to be preserved in a fossil. --------- Index fossils - The remains of living things that were widespread but only lived for a short part of Earth's history Trilobites - Index fossils that lived in underwater environments. ----------- Half-life - The time it takes for half the mass of a radioactive element to change into a new product. Absolute Age - The age of a rock in years. Eras - Long stretches of time in Earth's history. -------------------------- Eras: 4) Cenozoic 3) Mesozoic 2) Paleozoic 1) Precambrian Precambrian - Earth's earliest era. The formation of Earth marks this era's beginning. This era lasted 4 billion years. Paleozoic - fossils of the first land life date back to this era. The Appalachian Mountains formed late in this era. Mesozoic Era - (Middle Era) The continents began to break apart during this era,oceans filled in between the land masses, and the climate became milder. Fossils of the first mammals and birds date back to this era. Dinosaurs became extinct by the end of Mesozoic. ----------------------- Cenozoic - The era in which we live. It began about 70 million years ago.Several ice ages have occured during this era when vast glaciers covered much of the land. Fossils show that mammals became larger during the Cenozoic Era. |