Brianna_Monteil_Chapter_7_8

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Metropolitan Community College, Kansas City *

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101

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Geology

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Oct 30, 2023

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Chapter 7 Geologic Time & Chapter 8 Earth’s History Assignment 1. Distinguish between numerical dates and relative dates. Relative dates refer to determining if a rock or geological event is younger or older than another without a specific age – rocks on the bottom are the oldest while rocks on the top are the youngest. Numerical dates refer to finding the precise age of a rock or landform with specific practices like radioactivity that do not rely on the ages and context of other rocks. 2. What is the significance of an unconformity? Unconformities are significant because they represent a gap in the rock record which can be because of a lack of deposition or erosion. This means that there are no rocks that are representative of Earth’s history during that time and in that place. 3. Distinguish among angular unconformity, disconformity, and nonconformity. ● Angular unconformity – when sedimentary rocks are deposited onto deformed sedimentary strata; deformation could be because of tilting, folding, and/or faulting. ● Disconformity – where either non-deposition or erosion occurred; layers of rock that could have been present are absent. ● Nonconformity – occurs when sedimentary rocks are deposited on top of igneous and metamorphic rocks. 4. How do fossils serve as time indicators and what is the role they play in correlation? Fossils provide evidence of evolution and correlate to the units of the geological time scale. 5. List three types of radioactive decay. For each type, describe how the atomic number and atomic mass change. ● Alpha decay – when an alpha particle, consisting of two protons and neutrons, is emitted from the nucleus. This lowers the atomic number by four and lowers the atomic mass by four. ● Beta decay – when a neutron splits into a proton and electron. This increases the atomic number by one with the same atomic mass as the parent isotope. ● Electron capture – when a proton in the nucleus captures an electron and becomes a neutron; the atomic mass stays the same while the atomic number is reduced by one. 6. Explain the concept of “half-life.” “Half-life” is the calculated amount of time that half of the mass of an original (parent) radioactive isotope breaks down into a new (daughter) isotope.

7. Why is radiometric dating a reliable method for determining numerical ages? Radiometric dating is reliable because Each radioactive isotope used for dating has been decaying at a fixed rate since the formation of the minerals in which it occurs. 8. List the four basic units that make up the geologic time scale. Eons, eras, periods, and epochs. 9. Why is “zoic” part of so many names on the geologic time scale? “-Zoic” is part of the geologic time scale so much because it signifies the changes in life forms during each time period. 10. What term applies to all of geologic time prior to the Phanerozoic eon? Why is the span not divided into as many smaller time units as the Phanerozoic eon? The Precambrian applies to all geologic time prior to the Phanerozoic eon. This is because we do not have as many details or evidence when it comes to this time period.

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