Geologic Time and Relative & Absolute Dating

GEOL 1051 Exam 1                                                Name_____________________

Question 1: Geologic Time and Relative & Absolute Dating

For this questions you will determine the date (or date range) of each layer within the stratagraphic coloumn using absolute and relative dating techniques.  You will list the date(s), the age (Eon, Era, Period, and Epoch), and if the age was determined using aboslute or relative dating techniques.

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Layer A: Layer A is an igneous (volcanic) rock known as rhyolite.  By analyzing the rock, you find that about ¼ of the original Potassium-40 remains in the sample. (Note: Half-life of Potassium-40 is 1.3 Ga).

Numeric date(s): The age of rock will be 2.6 Ga. The ratio of parent-to-daughter isotopes changes with the passage of each successive half-life. In two half cycles about ¼ of the original Potassium-40 remains in the sample.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Archean Eon.

Type of dating technique (relative or absolute): It is absolute dating as it depends upon the radioactive decay of isotope of sample and thus one can get the numerical age of earth.

Layer B: Layer B is a limestone that contains many types of marine invertebrates such as: a trilobite (particular species has a known age of 468 to 450 Ma), and a brachiopod (particular species has a known age of 480 to 460 Ma).

Numeric date(s): Range lies between 433 to 488 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Ordovician Period.

Type of dating technique (relative or absolute): Relative dating as the relationship developed on the basis of relative age of fossils present in strata.

Layer C: Layer C is a shale that contains many types of marine invertebrates such as: a trilobite (particular species has a known age of 358 to 347 Ma), a clam (particular species has a known age of 351 to 320 Ma), and a coral (particular species has a known age of 356 to 335 Ma).

Numeric date(s): Range lies between 318 to 360 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Mississippian Period

Type of dating technique (relative or absolute): Relative dating as age assigned on the basis of relation of fossils present.

Layer D: Layer D is a limestone that contains many marine vertebrates such as: Schizolepis (an extinct genus of fish) (particular species has a known age of 311 to 287 Ma), Platysomus (another extinct genus of fish) (particular species has a known age of 308 to 272 Ma), and a spiny shark (particular species has a known age of 315 to 301 Ma).

Numeric date(s): Range lies between 250 to 318 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Permian and Pennsylvanian Period.

Type of dating technique (relative or absolute): Relative dating as age assigned on the basis of relation of fossils present.

Layer E: Layer E is a mudstone that does not contain any fossils; however, there is an ash layer above (Layer F) which has been radiometric dated to be 276 million years old.  Below Layer E is Layer D, which you previously analyzed.  Determine the following for layer E:

Numeric date(s): Range lies between 276 to 299 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Permian Period.

Type of dating technique (relative or absolute): Relative Dating as it follows the conditions of superposition principle for their age.

Layer G: Layer G is a sandstone that contains the following terrestrial vertebrates: Eutriconodont (an early mammal) (particular species has a known age range of 183 to 84 Ma), Stegosaurus (known age range is 155 to 150 Ma), and a Seismosaurus (a type of long-neck dinosaur) (known age range is 155 to 145).

Numeric date(s): Range lies between 65 to 204 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Cretaceous and Jurassic Period.

Type of dating technique (relative or absolute): Relative dating as the relationship developed on the basis of relative age of fossils present in strata.

Layer H: Layer H is a shale that contains the following dinosaurs: Carnotaurus (a large theropod) (know age range is 70 to 75 Ma), Styracosaurus (a type of Ceratopian) (76 to 73 Ma), and Ankylosaurus (74 to 67 Ma)

Numeric date(s): Range can be 65 to 144 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Cretaceous Period.

Type of dating technique (relative or absolute): Relative dating as the relationship of the strata depends upon the fossils present.

Layer I: Layer I is a fine silt stone that contains the following mammals: Hyracotherium (the earliest ancestor to the horse) (known range of 55-45 Ma), an early primate (particular species has a known range of 56 to 50 Ma), and a multituberculate (an early mammal group that is now extinct) (particular species has a known range of (68 to 48 Ma).

Numeric date(s): Rang can lie between 34 to 144 Ma.

Age name (Eon, Era, Period, Epoch) (note: list as many subdivided names as the time scale provides): Eocene and Paleocene Epoch and some later parts of Cretaceous Period.

Type of dating technique (relative or absolute): Relative dating as the relationship of the strata depends upon the fossils present.

Layer K: Layer K is a mudstone that does not contain any fossils; however, there is an ash layer bellow (Layer J) which has been radiometric dated to be 7 million years old.  above Layer K is Layer L, which you will analyze in the next question.  You may want to examine layer L before examining Layer K.

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