Grade 11 Earth Science - Earth's History, Geological Time Scale
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Course
Science
Institution
Sixth Year / 12th Grade
Discussion notes about the earth's history for STEM Grade 11 1st final term. It tackles relative and absolute dating, key ideas of relative dating, the age of the earth, and geological timescale.
Earth's History
Thursday, 25 November 2021 7:25 PM
Earth's History Can Be Proven in 4 Ways
1. Relative Dating
2. Absolute Dating
3. Index Fossils
4. Geologic Time Scale
RELATIVE DATING
- Qualitative
- Depends on the depth
Sedimentary rocks are useful in Relative Dating
Formed from fragments of other types of rocks
New sedimentary layers are always flat
Fossils are deposited in the sedimentary layers of rocks
• Stratigraphy - study of layered rocks
KEY IDEAS OF RELATIVE DATING
1. Law of Original Horizontality
- Originally formed in horizontal layers
2. Law of Superposition
- Oldest rocks are in the bottom layer
3. Principle of Lateral Continuity
- Rock layers extend laterally and cover very broad areas; continuous layer
- Example: Grand Canyon
4. Principle of Crosscutting Relations
- Layer must always be older than any feature that cuts or disrupts it.
- Only applies faults, intrusions, and unconformities
5. Idea of Unconformities
- Surface of erosion
ABSOLUTE DATING
- Quantitative
- Measuring the absolute age
- Makes use of information from radioactive decay
- Parent isotope -> daughter isotope
• Radiometric Dating
Potassium Argon (K-40 t1/2 = 1.25B yrs; rocks older than 100,000 yrs)
Uranium-Lead (U-238 t1/2 = 4.5B yrs; for rocks older than 10M yrs)
Rubidium-Strontium (Rb-87 t1/2 = 49B yrs; rocks older than 10M yrs
Carbon-14 (t1/2 = 5730 yrs; for rocks that lived within the last 50,000 yrs)
AGE OF THE EARTH
- 4.6 billion years of history
- Based from the radioactive isotopic dating of meteorites
- Oldest rock - 3.8 billion years old
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