Geochronology, Homeschooling Blog, Grade 7

Geochronology

Geochronology is the scientific discipline of an age to geological and fossilized material, geological age dating. There are two ways to date a sample: relative age dating and absolute dating.



Absolute dating gives us the actual age of a rock or fossil using the rate in which a radioactive substance within the sample decays, you get a specific number. Relative dating tells us which rock, fossil, or event preceded. It gives us the order of things and how old something is to another. Relative dating uses geologic sequencing.

The Law of Uniformitarianism assumes all the geological processes that happen today happen the same way in our distant past: erosion, tectonics, and volcanism.

Geological Rules When Study the History of the Earth:

  • Sedimentary rocks form from sediments deposited on the bottom of a body of water.

  • Erosion and weathering of rock occurs on the surface and not underwater.

  • We assume the layers of sedimentary rock on the bottom are the oldest. This is called the Law of Superposition.

  • Sedimentary layers are deposited horizontally, but may be deformed through folding, faulting, and tilting. This is called the Law of Original Horizontality.

  • Igneous intrusions are younger than the rocks they metamorphose.
    Faults are younger than the rocks they cut through.

  • Uplift, weathering and erosion, subsidence forms unconformities. Unconformities are a missing part of the subterranean rock record.

  • Inclusions must be older than the rocks they are in. The Law of Inclusions. For example igneous particles are older than the conglomerate rock they are in.



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