Section 1: Determining Relative Age
Vocabulary
Relative Age - The age of an object in relation to other objects.
Uniformitarianism - The principle that by studying the present, we can learn about the past.
Law of Superposition - The law that a rock layer is older than the ones above it and younger than the ones below it if the rock layers are not disturbed.
Uniformitarianism - The principle that by studying the present, we can learn about the past.
Law of Superposition - The law that a rock layer is older than the ones above it and younger than the ones below it if the rock layers are not disturbed.
Key Concepts
- According to the principle of uniformitarianism, the forces that are changing Earth's surface today are the same ones that changed Earth's surface in the past.
- Uncomformities are interruptions in the rock record, like when rock layers are eroded of sediment is not deposited for a long time.
- Scientists use the law of superposition and the law of crosscutting relations to determine relative age.
Section 2: Determining Absolute Age
Key Concepts
- Because the rates of erosion and deposition can be changed, they are imprecise methods of absolute dating.
- Radioactive decay is constant and unchanged by environmental conditions.
- Scientists use carbon dating to find the absolute age of organic materials. Carbon-14 combines with oxygen, creating carbon dioxide - which contains either carbon-12 or carbon-14. Plants absorb the carbon dioxide and animals eat those plants; therefore, every living things contains carbon. Scientists find the ratio of carbon-12 to carbon-14 in the organic material, and then compare it to the ratio in a living organism (because it is usually constant in a living organism).
Section 3: The Fossil Record
Vocabulary
Fossil - The remains of a plant or animal that lived in a previous geologic time.
Paleontology - The study of fossils.
Amber - Hardened tree sap that encases an organism.
Tar seeps - Formed when thick petroleum oozes to Earth's surface; they are commonly covered by water, so when animals drink the water they become trapped in it.
Freezing - When the low temperature of frozen soil and ice can preserve an organism.
Paleontology - The study of fossils.
Amber - Hardened tree sap that encases an organism.
Tar seeps - Formed when thick petroleum oozes to Earth's surface; they are commonly covered by water, so when animals drink the water they become trapped in it.
Freezing - When the low temperature of frozen soil and ice can preserve an organism.