M4 L9: Relative and Absolute Dating

• ● Earth is approximately 4.5 billion years old; the crust’s rocks are analyzed through these dating techniques.
• RELATIVE DATING

  ● Qualitative data; the comparison of the layers of rock.
• Principles

  ● Original Horizontality

  ● Superposition

  ● Lateral Continuity

  ● Cross-cutting Relationship

  ● Inclusions

  ● Unconformities
• ● Original Horizontality

  ○ Rocks are deposited in nearly horizontal layers. Although due to deformation, it may be disturbed and lose its horizontality.

  ○ Deposition has a natural horizontality.
• ● Superposition

  ○ In a series of layered sedimentary rocks, the bottom rock is the oldest while the top layer is the youngest.

  ○ The one at the bottom formed first.
• ● Lateral Continuity

  ○ rock layers may extend laterally and cover broad areas. This may be limited when a barrier prevents the deposition of the sediments.

  ○ Initially they were connected but due to extension/space nagkakahiwalay sila pero same age pa rin.
• ● Cross-cutting Relationship

  ○ Older rocks may be cut by the rock developed from fault, dike, or magma intrusion. This means that the intrusions are younger rocks compared to the surrounding rock.

  ○ Occurs kapag may plutonic igneous rock na nag-intrude and nag-erode.
• ● Inclusions

  ○ Rocks containing smaller pieces of rocks (inclusions) are younger compared to the inclusions it contains.
• ● Unconformities

  ○ Missing strata may happen when a layer of rock has been deformed or eroded before the deposition of a new stratum.

  ○ Angular: A sedimentary layer is deposited in tilted or folded sedimentary rocks that are not parallel to the unconformity surface.

  ○ Disconformity: a sedimentary layer is deposited in an eroded horizontal layer.

  ○ Nonconformity: deposition over an eroded plutonic igneous rock.
• ABSOLUTE DATING

  ● Uses radiometric dating techniques to determine how long ago the rock formed in the exact number of years. Near approximation only.

  ● Provides a range of years by computing the radioactive decay of isotopes.
• ABSOLUTE DATING

  ● Isotopes: Atoms of the same element with varying numbers of neutrons. The radioactive form of an element.
• ABSOLUTE DATING

  ● Radioactive Decay: Spontaneous transformation of one element into another. The only way that this can happen is by changing the number of protons in the nucleus. An unstable radioactive element changes into a stable element.
• ABSOLUTE DATING

  ● Half-life: the time needed for half of a sample of radioactive decay to undergo radioactive decay and form daughter products.