Understanding Geological Time and Radiometric Dating

1. Applying the Law of Superposition of Strata: The order of deposition layers has been A, B, C, D, E.

2. The Material: A concordant igneous body, D, is the youngest.

3. Intrusion: F is discordant and cuts all layers of strata.

4. Inclination and Erosion: The pivoting has inclination and erosion.

5. After Forming: G, H, I, J, K were deposited angularly.

6. Emersion: Unconformity and erosion create an irregular surface, indicating that the river valley was a vacuum.

Radiometric Method: To establish age with greater accuracy, minerals in the rocks formed x atoms, including some radioactive elements such as Pb, U, Rb, and K. These radioactive elements spontaneously decay, leading to instability and the formation of child elements. Radiometric dating involves the decay of radioactive isotopes over a fixed time. The parent radioactive element (N) decays into its stable element (H) over its period of disintegration (T). With these data, we can obtain the absolute age of minerals or rocks.

Conditions for Using Radiogenic Elements:

• a) The element must be a common chemical.
• b) It should have an intermediate half-life.
• c) The child element must be distinguishable from the parent at the time of its formation.

Division of Geologic Time: The time scale is based on comprehensive geological and biological events. The chronostratigraphic scale has two types of units:

• Lithostratigraphic Units: Defined from the lithologic character of the stratigraphic succession.
• Biostratigraphic Units: Defined from the paleontological features presented in strata.

The unit is the geologic eon, which has the greatest range in the geological timeline. There are three eons:

• Archaic: 4550 Ma to 2500 Ma
• Proterozoic: 2500 Ma to 570 Ma
• Phanerozoic: Usually 570 Ma to present

The Precambrian eons, including the Proterozoic and Archaic, are divided into eras:

• Paleozoic (570 Ma to 250 Ma)
• Mesozoic (250 Ma to 65 Ma)
• Cenozoic (Tertiary and Quaternary, 65 Ma to present)

The Phanerozoic eras are divided into periods, including:

• Cambrian
• Ordovician
• Silurian
• Devonian
• Carboniferous
• Permian
• Triassic
• Jurassic
• Cretaceous
• Tertiary
• Quaternary

Periods are divided into epochs, and these epochs are named after the geographic location where they were first identified, often ending with the suffix '-ian' or '-ense.'