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33 terms

Chapter 21

STUDY
PLAY
Deposition of sediment with each new layer younger than the layer below is referred to as the princile of
superposition
In a sequence of rock layers we find fossils of trilobites and dinosaurs. The trilobite is at the bottom of he rock sequence in layer 1. The dinosaur fossil are found in layers 2, deiectly above the trilobite fossils. We conclude that
the processes of erosion have created a gap between the ages of the trilobite and the age of the dinosaur.
The principle of superposition states that the top layer of the rock is
the youngest
The scientific principle hat assumes that the different forms of animals throughout the Earth's past occurred in a definite order is called the principle of
faunal succession
Conditions for the preservation of fossils are best achieved
on the floors of shallow seas
The principle of faunal succession is based on the four assumptions of (1) the validity of the principle of superposition;
(2) the sequence of fossils are the same everywhere (3) rock layers of different ages will contain different types of fossils; and (4) the validity of the principle of original horizontality
The rather simple idea that,unless disturbed, younger sedimentary layerd overlie older layers, is referred to as the principle of
superposition
In a sedimentary rock that contains inclusions of metamorphic rock, the inclusions must be
older than the sedimentary rock
Uniformitarianism is the assumption that
present day processes also occurred in the geologic past
To date relatively young rocks and materials, we use the decay of
carbon -14 to nitrogen -14
To date the age of the Earth's, we look for rocks with a high percentage of
uranium-238 to lead-206
The Earth's age has been determined to be
4.5 billion years old by using meteorites
Radiocarbon datingis limited to the remains of plants and animals that died no longer than about
5700 years ago
If a radioactive element has a half-life of 704 million years, and the amount of parent material remaining is one-eighth of the original amount of parent material, the specimen is
2,112,000,000 years old
If the half-life of some radioactive element is 1 billion years, and a mass of rock originally contained 100 g of that element, how many grams of the radioactive element would be left after three billion years had passed
12.5 g
The isotope most useful for dating rocks from the late Pleistocene is
carbon-14
Life forms in the Precambrian include
stormatolites and certain primitive blue-green algae
The oldest known fossils are
algae and bacteria
You would expect to find the least number of fossils in rocks from the
Precambrian era
The Paleozoic era begains with he Cambrian and concludes with the
Permian period
The Ordovician period is most noted for the
great diversity in marine life
The formation of the supercontinent of Pangaea
resulted from the collision of all major land masses
The climatic zones of Pangaea ranged from
glaciation in the south, and a mild temperate climate in the north
Ancient geologic processes as revealed in Paleozoic rock layers were
very similar to processes of erosion and sedimentation
Life first started to flourish on Earth with organisms that were easily preserved as fossils about
543 million years ago
The high concentration of iridium at the Cretaceous Tertiary boundary is most likely attributed to
meteorite bombardment
The Mesozoic era is known a the age of the
reptile
Iridium is an element that is relatively
rare on Earth, but very common in meteorites
The Cenozoic Era is known as the
age of the mammals
Uplift of the Rocky Mountains was a result of
compressional forces
During the Pleistocene ice age
there were several episodes of glacial advance and retreat
In general, when we refer to the time of the "Ice Age" we are referring to the
Tertiary era
The extensive glaciation of the Pleistocene caused sea level to
drop because a great deal of water was bound in glaciers