Mesozoic Era
Second of Earth's three major geologic eras that began 251 million years ago and ended 65.5 million years ago; this era is best known as the time of the dinosaurs
Radioactive
When an atom's nucleus is unstable and will emit energy or particles in an attempt to become more stable
Reptile
A vertebrate whose temperature is determined by the temperature of its environment, that has lungs and scaly skin, and that lays eggs on land
Paleontologist
A scientist who studies fossils to learn about organisms that lived long ago
Fossil
Preserved remains or traces of an organism that lived in the past
Carbon Sink
Anything that absorbs more carbon that it releases
Natural Selection
The process through which individuals that are better adapted to their environments are more likely to survive and reproduce than other members of the species
Extinction
The dying out or termination of a species
Fault
A break in Earth's crust along which rocks move
Mass extinction
When many types of living things become extinct at the same time
Period
One of the units of geologic time into which geologists divide eras
Mold
A type of fossil that is a hollow area in sediment in the shape of an organism or part of an organism
Geologic Time Scale
A record of the geologic events and life forms in Earth's history
Comet
A loose collection of ice and dust that orbits the sun, typically in a long, narrow orbit
Unconformity
A rock or sediment surface separating two layers of different ages
Radioactive Decay
The process in which radioactive elements break down
Cenozoic Era
Third of the major eras of Earth's history, beginning about 65.5 million years ago and extending to the present; during the Cenozoic, the continents assumed their modern configuration and Earth's flora and fauna evolved toward those of the present
Index Fossil
Fossil used for indexing and defining geologic periods
Survival
The act or fact of living or continuing longer than another person or thing
Half-Life
The time it takes for half of the atoms of a radioactive element to decay
Absolute Age
The age of a rock given as the number of years since the rock formed
Carbon Cycle
The circulation of carbon in various
Trace Fossil
A type of fossil that provides evidence of the activities of ancient organisms
Invertebrate
An animal without a backbone
Era
One of the three long units of geologic time between the Precambrian and the present
Mammal
A vertebrate whose body temperature is regulated by its internal heat and that has skin covered with hair or fur and glands that produce milk to feed its young
Cast
A fossil that is a solid copy of an organism's shape, formed when minerals seep into a mold
Extrusion
An igneous rock layer for med when lava flows onto Earth's surface and hardens
Extinct
Term used to refer to a group of related organisms that has died out and has no living members
Relative Age
The age of a rock compared to the ages of other rocks
Law of Superposition
The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger that the layer below it
Amphibian
A vertebrate whose body temperature is determined by the temperature of its environment and that lives its early life in water and its adult life on land
Carbon Film
A type of fossil consisting of an extremely thin coating of carbon on rock
Intrusion
An igneous rock layer formed when magma hardens beneath Earth's surface
Folding
The permanent bending or curving of a previously flat layer of rock
Isotope
Atoms of the same element that have numbers of neutrons
Petrified Fossil
A fossil in which minerals replace all or part of an organism
Evolution
Change over time; the process by which modern organisms have descended from ancient organisms
Endangered Species
A species at high risk of extinction
Paleozoic Era
A major interval of geologic time that began 542 million years ago and ended 251 million years ago with the greatest extinction event in Earth's history
Precambrian
Period of time that extends from about 4.6 billion years ago (the point at which Earth began to form) to the beginning of the Cambrian period 542 million years ago
Vertebrate
An animal with a backbone
When might preserved remains of an entire organism form?
When an event such as a quick burial or freezing preserves an entire organism
Which of the following fossil types is best described as forming when minerals replace all or part of an organism's
body?
A petrified fossil
What has the study of fossils allowed scientists to do?
Describe past environments and the history of life.
Footprints and trails are examples of trace fossils.
True
Knowing nothing else, what could the relative age of two rocks tell you about them?
One rock is older than the other.
What would a geologist do if he or she wanted to determine the age of rock layers at a given location using relative
age?
Find the relative age of one rock layer at the given location.
How does folding change rock layers?
Folding can change the position in which rock layers appear.
Sometimes, layers of rock are overturned so frequently that the youngest rock layer may appear on the bottom, which
is the reverse of what is ordinarily expected.
True
Which of the following statements about radioactive decay is true?
During radioactive decay, atoms break down, releasing particles or energy.
Which of the following terms refers to the time it takes for one-half of the radioactive atoms in a sample of a
radioactive element to decay?
Half-life
Geologists use radioactive dating to
Determine the absolute age of rocks.
If the half-life of a 20.0 g sample is known to be 24 minutes, how long will it take for only 5.0 grams of the sample to
remain?
48 minutes
The geologic time scale originally ordered Earth's rocks by
Relative age.
Where did scientists initially get information to develop the geologic time scale?
They studied rock layers and index fossils around the world.
Which of the following is the longest division of geologic time?
Era
Geologists divide Earth's long history into smaller units that make up the geologic time scale.
True
Which of the following gases was most likely present in Earth's earliest atmosphere?
Hydrogen
Which of the following statements accurately describes the development of the geologic time scale?
Scientists developed the geologic time scale by studying rock layers and index fossils worldwide.
What can scientists learn from the rate at which radioactive elements decay?
A rock's actual, or absolute, age
The relative age of a rock is
its age compared with the ages of other rocks.
After six half-lives, what percentage of a radioactive sample will remain?
1%-3%
Earth's atmosphere, oceans, and continents began to form during the first several hundred million years of
Precambrian time.
True
A mold forms when minerals replace all or part of an organism.
False
How are a mold and a cast related?
A mold and a cast fossil are related because both are a result from a decayed organism that once lived. In
addition, both fossils create the shape of that organism.
If the following graph represents the decay of strontium-90 in an igneous rock, what event occurred at 0 years on the
horizontal axis?
At the 0 year mark on the horizontal axis, I think strotium-90 formed an igneous rock. The chart shows the
percentage of the radioactive element's remains of the rock. At the point (0,100) mark, the igneous rock still
has 100% of its particles. As half-ti
Suppose you found a fossil of a clamshell. What can you conclude about the once-living organism and how it
became a fossil?
If I found a fossil of a clamshell, I can conclude that the body of the clam was either eaten by a predator or
it decomposed when it died. If this fossil was not eaten by a predator, then I can conclude that the area
where the fossil was found, at one poi
Which of the following is an example of an environmental pressure?
A lake that is gradually running out of water
Which of the following is the most likely example of a favorable mutation?
A mutation that makes a rabbit able to run faster
How does carbon become locked inside Earth?
The carbon-rich bodies of plants and animals decay into Earth as they die.
Carbon emissions lead to global warming by trapping the sun's heat in the atmosphere.
True
Which of the following is an example of an effect of natural selection?
Favorable environmental conditions cause an increased food supply.