Earth Science Homework 8
After three half-lives, ________ of an original, radioactive, parent isotope remains and the rest has decayed into the daughter isotope.
12.5% or one-eighth (1/8)
During alpha emission, the mass number is reduced by ________ and the atomic number is decreased by ________.
4; 2
________ is the belief that Earth was shaped by large-scale geologic calamities.
Catastrophism
We now live in the ________ era.
Cenozoic
Why isn't the Precambrian more finely divided into subdivisions like periods and epochs?
Fewer and less diverse fossils exist in Precambrian rocks.
Who first formulated the principle of uniformitarianism?
Hutton
________ occurs when mineral-rich groundwater permeates porous tissue and fills the empty spaces, hardening into a fossil.
Permineralization
All of geologic time prior to the beginning of the Paleozoic era is commonly referred to as the ________.
Precambrian
The earliest 88% of geologic time is represented by the time span informally called the ________.
Precambrian
Which of the following would be the best method for obtaining a numerical age for sedimentary rocks?
Relate the sedimentary rocks to a datable igneous mass, such as a dike or sill.
________ is the branch of geology that studies rock layers.
Stratigraphy
Which of the following describes radioactive decay by beta particle emission?
The atomic number of the daughter isotope is one more than the parent; the mass numbers are the same.
Which of the following is an essential characteristic of an index fossil?
The organism lived for a very limited period of geologic time.
Why do the eras of the Phanerozoic eon all end with "zoic"?
These names refer to life or living things; they invoke the changes in fossil organisms from one era to the next.
Which of the following periods belongs to the Mesozoic era?
Triassic
"This rock is 15 million years old" is an example of ________.
a numerical date
The principle of cross-cutting relationships states that geologic features that cut across rocks most form ________ the rocks they cut through.
after
Which of the following geologic observations would bear directly on working out the sequence of geologic events in an area?
an unconformity between a granite and a sandstone
A section of marine sediments is uplifted, folded, and then overlain by sandstone. What is the name of the resulting feature?
angular unconformity
One important limitation when using potassium-argon for age-dating is that ________.
argon is a gas and may leak from minerals, throwing off measurements
A sandstone is found to overlie a shale. The shale contains a volcanic ash layer that has been radiometrically dated to 84 million years ago. Both the shale and the sandstone are cut by a pluton of gabbro that has been dated to 60 million years old. How old is the sandstone layer?
between 84 and 60 million years old
Among the following radioactive parent isotopes, which has the shortest half-life?
carbon-14
Which of the following radioactive isotopes would be best for age-dating a rock from 50,000 years ago?
carbon-14
The process by which geologists identify and match sedimentary strata and other rocks of the same ages in different areas is ________.
correlation
A(n) ________ is an erosional unconformity with parallel beds or strata above and below.
disconformity
The longest subdivision of the geologic time scale is the ________.
eon
The shortest subdivision of the geologic time scale is the ________.
epoch
A set of fossil organisms found together in a given layer is called a(n) ________.
fossil assemblage
Which of the following is an example of a trace fossil?
fossil dung
The principle of ________ is the concept that ancient life forms evolved in a definite order, and therefore, their fossils can help determine the geologic ages of strata.
fossil succession
The amount of time it takes for half of the remaining radioactive isotopes to decay is the ________ of an isotope system.
half-life
Which of the following fossils would be a good example of an index fossil?
marine microfossils
The scientific study of fossils is called ________.
paleontology
Which of the following principles addresses rock fragments being enclosed within another rock layer?
principle of inclusions
A principle by which sedimentary beds originate as continuous layers until they grade into another rock type or thin out is called the ________.
principle of lateral continuity
Most igneous rocks can be dated directly by ________ methods.
radiometric
Using the known rates of radioactive decay to date the crystallization of certain minerals is known as ________ dating.
radiometric
Which of the following is an example of a nonconformity?
shale sitting atop granite
The principle of ________ states in an undeformed sequence of sedimentary rocks each bed is older than the one above and younger than the one below.
superposition
An unconformity is a buried ________.
surface of erosion separating younger strata above from older strata below
To calculate the age of a rock, you need to know the parent-daughter isotope ratio and ________.
the half-life of a radioactive isotope
The idea of ________ suggests that the physical, chemical, and biological laws that operate today have also operated in the geologic past.
uniformitarianism
You notice preserved ripple marks in the mountains, then later at the beach you see ripple marks forming in the sand. Which of the following best describes how the ripple marks in the mountain formed?
uniformitarianism
A worm would stand a poor chance of being fossilized because ________.
worms have no hard parts
