Relative vs Absolute Dating Important Facts Uniformitarianism The

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Relative vs. Absolute Dating

Relative vs. Absolute Dating

Important Facts

Important Facts

Uniformitarianism The Present is the KEY to the PAST. Laws of nature are the

Uniformitarianism The Present is the KEY to the PAST. Laws of nature are the same now as they have always been. Past events explained and estimated by modern processes. Charles Lyell credited with this concept. Explained in his book “The Principles of Geology. ”

Other Important Words… Lithification: the consolidation of a loosely deposited sediment into a hard

Other Important Words… Lithification: the consolidation of a loosely deposited sediment into a hard sedimentary rock. Strata: rock layers

Original Horizontality When sedimentary rock layers form, they are “created” in a horizontal fashion.

Original Horizontality When sedimentary rock layers form, they are “created” in a horizontal fashion.

And, most importantly…

And, most importantly…

Relative vs. Absolute Age of Rock Relative Dating: determination of the age of a

Relative vs. Absolute Age of Rock Relative Dating: determination of the age of a rock or geologic event by comparing with other rocks/geologic events Can you infer who is older? She is.

4 ways to determine relative age. (Also called the Principles of Geology)

4 ways to determine relative age. (Also called the Principles of Geology)

Law of Superposition In undisturbed layers of sedimentary rock or lava flows… Top Layer

Law of Superposition In undisturbed layers of sedimentary rock or lava flows… Top Layer = Youngest Bottom Layer = Oldest

Cross-Cutting Relations Any feature that cuts across a rock or layer of sediment is

Cross-Cutting Relations Any feature that cuts across a rock or layer of sediment is younger than the rock or layer it cuts Yo un ge st La ye r

Law of Included Fragments Sediments are older than the cement and rock they are

Law of Included Fragments Sediments are older than the cement and rock they are part of

Fossil Correlation The same group of fossils are of the same age, and therefore,

Fossil Correlation The same group of fossils are of the same age, and therefore, strata containing them are also of similar age.

There some speed bumps on the road to Relative Dating

There some speed bumps on the road to Relative Dating

Uncomformity A gap or missing layers of rock due to erosion.

Uncomformity A gap or missing layers of rock due to erosion.

Angular Unconformity Older rock under the line of erosion are tilted at an angle,

Angular Unconformity Older rock under the line of erosion are tilted at an angle, while the younger strata above are horizontal.

Disconformity Strata above AND below the line of erosion are horizontal.

Disconformity Strata above AND below the line of erosion are horizontal.

Nonconformity Unconformity that separates igneous or metamorphic rock from a layer of sedimentary rock.

Nonconformity Unconformity that separates igneous or metamorphic rock from a layer of sedimentary rock.

Relative vs. Absolute Age of Rock Absolute: A form of geologic dating that gives

Relative vs. Absolute Age of Rock Absolute: A form of geologic dating that gives an actual date/age in history that the item was formed or died. 6 months 82 years

Phenomenon of Radioactivity Some elements, such as uranium (U) and thorium (Th) are unstable.

Phenomenon of Radioactivity Some elements, such as uranium (U) and thorium (Th) are unstable. They decay spontaneously.

The Atom

The Atom

Radioactive Decay 238 U spontaneously emits a particle from its nucleus called an alpha

Radioactive Decay 238 U spontaneously emits a particle from its nucleus called an alpha particle (2 protons + 2 neutrons).

Radioactive Decay

Radioactive Decay

Uranium-Thorium Decay

Uranium-Thorium Decay

Beta Particle Emission But, 23490 Th is also unstable, and it emits a beta

Beta Particle Emission But, 23490 Th is also unstable, and it emits a beta particle …

Thorium-Protactinium Decay

Thorium-Protactinium Decay

U – Pb Series This process is called radioactive decay, and eventually uranium (parent)

U – Pb Series This process is called radioactive decay, and eventually uranium (parent) decays to lead (daugher product)

U – Pb Series The rate at which this process occurs is measured in

U – Pb Series The rate at which this process occurs is measured in terms of a “half life”.

Half Life= Number of years for ½ of the original number of atoms to

Half Life= Number of years for ½ of the original number of atoms to decay from U to Pb.

Radiometric Dating Assume: Rate of decay (half life) of long-lived elements has not varied

Radiometric Dating Assume: Rate of decay (half life) of long-lived elements has not varied since the Earth was formed. This is an example of uniformitarianism.

Half-Lives of Radioactive Isotopes

Half-Lives of Radioactive Isotopes

Examples of very old rocks found on Earth ü 3. 4 billion year old

Examples of very old rocks found on Earth ü 3. 4 billion year old granites – South Africa ü 3. 7 billion year old granites – Greenland ü Oldest terrestrial rocks ~ 4 billion years ü Central Canada and Central Australia ü These are deep in the interiors of the continents ü Core drilling aids in excavation of these rocks.