Topic 9 – Geologic Time ( pgs. 423 – 427 )
The principle of superposition states that in undisturbed layers of rock, the oldest layers are always on the bottom and the youngest layers are always on the top.
As new layers of sediment form sedimentary rock, the layers can be identified. This layering is called strata.
Geologists use a technique called relative dating, to find the order in which events occurred. The relative age of the rock is determined by its position within the strata. Fossils found in a layer can help to identify the age of the rock. If the fossil was on the Earth for a short time and widespread then it is called an index fossil.
Clues from Technology
- Over billions of years, some elements will change into other elements – uranium is such an element - in 4.5 billion years, half of the uranium will change into lead (which will not change). The uranium is called the parent element. This time period is called the half-life of uranium
- By measuring the amounts of change in a sample, scientist can clculate the absolute age of the rock. This is called Radiometric Dating
- Scientists also use a process called radiocarbon dating (which uses carbon-14, a rare form of carbon, as its parent material)
- All organisms take in carbon-14 to build cells and tissue. The carbon-14 changes to nitrogen gas (when the animal dies) in a half-life of 5730 years. The amount of carbon-14 left in the tissue allows scientists to determine the age of the remains
Geological Time Scale
The geological time scale is a division of Earth’s history into smaller units based on the appearances of different life forms.
The largest divisions are called eons, which are divided into eras and then further divided into periods.
Rodinia was the first supercontinent and Pangaea was the second supercontinent.
Terms
Principle of Superposition- A geological theory; according to this theory, in undisturbed layers of rock, the oldest layers will be on the bottom and the youngest on top.
Strata-a layer of material, naturally or artificially formed, often one of a number of parallel layers one upon another.
Index Fossil- the fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found. The best type of index fossils are usually those of swimming or floating organisms that evolved quickly (and therefore did not cover a long span of geologic history) and were able to spread over large areas. Ammonites and graptolites are good index fossils.
Half-Life- the time required for half of a quantity of radioactive material absorbed by a living tissue or organism to be naturally eliminated ( biological half-life ) or removed by both elimination and decay ( effective half-life )
Radiometric Dating-the method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products (in this case strontium). The object's approximate age can then be figured out using the known rate of decay of the isotope. For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms. Radiocarbon dating is one such type of radiometric dating.
Radiocarbon Dating- A technique for measuring the age of organic remains based on the rate of decay of carbon 14. Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms. Also called carbon-14 dating .Periods- A division of geologic time that is longer than an epoch and shorter than an era. Eons- The longest division of geologic time , containing two or more eras.Eras- A division of geologic time , longer than a period and shorter than an eon. A division of geologic time , longer than a period and shorter than an eon.
Precambrian- of, denoting, or formed in the earliest geological era, which lasted for about 4 000 000 000 years before the Cambrian period
Rodina- the earliest supercontinent formed 11000 years ago
Paleozonic Era- the second era on the geologic time scale
Mesozonic Era- the third era on the geologic time scale
Cenozonic Era- the latest era on the geologic time scale (present life)
Pangaea-the name of the second supercontinent thought to have existed about 350 million years ago
Laurasia- the northern part of Pangaea
Gondwanaland- the southern part of Pangaea
Principle of Superposition- A geological theory; according to this theory, in undisturbed layers of rock, the oldest layers will be on the bottom and the youngest on top.
Strata-a layer of material, naturally or artificially formed, often one of a number of parallel layers one upon another.
Index Fossil- the fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found. The best type of index fossils are usually those of swimming or floating organisms that evolved quickly (and therefore did not cover a long span of geologic history) and were able to spread over large areas. Ammonites and graptolites are good index fossils.
Half-Life- the time required for half of a quantity of radioactive material absorbed by a living tissue or organism to be naturally eliminated ( biological half-life ) or removed by both elimination and decay ( effective half-life )
Radiometric Dating-the method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products (in this case strontium). The object's approximate age can then be figured out using the known rate of decay of the isotope. For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms. Radiocarbon dating is one such type of radiometric dating.
Radiocarbon Dating- A technique for measuring the age of organic remains based on the rate of decay of carbon 14. Because the ratio of carbon 12 to carbon 14 present in all living organisms is the same, and because the decay rate of carbon 14 is constant, the length of time that has passed since an organism has died can be calculated by comparing the ratio of carbon 12 to carbon 14 in its remains to the known ratio in living organisms. Also called carbon-14 dating .Periods- A division of geologic time that is longer than an epoch and shorter than an era. Eons- The longest division of geologic time , containing two or more eras.Eras- A division of geologic time , longer than a period and shorter than an eon. A division of geologic time , longer than a period and shorter than an eon.
Precambrian- of, denoting, or formed in the earliest geological era, which lasted for about 4 000 000 000 years before the Cambrian period
Rodina- the earliest supercontinent formed 11000 years ago
Paleozonic Era- the second era on the geologic time scale
Mesozonic Era- the third era on the geologic time scale
Cenozonic Era- the latest era on the geologic time scale (present life)
Pangaea-the name of the second supercontinent thought to have existed about 350 million years ago
Laurasia- the northern part of Pangaea
Gondwanaland- the southern part of Pangaea