Chapter 9 Flashcards
(24 cards)
How old is a mammoth bone if 25 percent of the original carbon-14 remains in the sample? (Carbon-14 has a half-life of 5,730 years)
11,460 yrs old
Which of the following is least likely to be found as a fossil?
jellyfish imprint
What are glacial lake sediments that show cycles of deposition?
Thin layer of sediment deposited on a lakebed over the course of one year; usually found at the bottom of glacial lakes.
varves
Thin layer of sediment deposited on a lakebed over the course of one year; usually found at the bottom of glacial lakes.
In addition to help in dating, what else do tree rings, ice cores, and varve provide evidence for?
past climates
A fault upsets three older sedimentary rocks. What principle is displayed in this scenario?
cross-cutting relationship
Geologic principles such as superposition and cross-cutting relationships help determine the relative age of objects, which objects are older and which are younger.
To say “the present is the key to the past” is a way to describe which of the following principles?
The idea that the geologic processes that shape the land today have acted in basically the same way throughout Earth’s history.
uniformitarianism
The idea that the geologic processes that shape the land today have acted in basically the same way throughout Earth’s history.
Describe relative age dating
The age of an object in comparison with the age of other objects.
is the age of rocks and geologic features compared with other rocks and features nearby. Relative age dating does not provide actual numerical dates from the rock, it only organizes layers in chronological order. There are several principles geologists use to find the relative age of rocks.
Where are most fossils found?
sedimentary rock
What do inclusions in rocks indicate?
A piece of a rock that is caught up inside of another rock.
the inclusion is older than the rock it is found in.
is NOT a characteristic of index fossils?
A fossil that identifies and shows the relative age of the rocks in which it is found. Index fossils come from species that were widespread but existed for a relatively brief period of time.
long-lived
NOT used in the process of absolute dating?
index fossils
A fossil that identifies and shows the relative age of the rocks in which it is found. Index fossils come from species that were widespread but existed for a relatively brief period of time.
The oldest rocks are found _____ of a sequence.
on the bottom
Which conditions aid in the formation of fossils?
hard parts and fast burial
Carbon-14 is used for dating rocks that are about how old?
younger than 50,000 yrs
How are Carbon-14 and Uranium 238 similar?
both are radioactive elements
What is slowly seeped into the original wood in the formation of petrified wood?
minerals
radioactive element has the longest half-life?
Uranium 238
What do index fossils indicate?
the relative age of rock
What makes a species a good index fossil?
lived a short time and was abundant
What is a mold fossil?
impression left behind by an organism
Fossils can provide clues about past climates and mass extinctions.
True
What is the law that sediments are always deposited in flat, horizontal layers?
orginal horizontality
Principle that states that sedimentary layers were horizontal or flat-lying at the time they were deposited.
Trace Fossil
Evidence of the activity of an ancient organism. Examples include tracks, trails, burrows, tubes, boreholes, and bite marks.
Inclusion
A piece of a rock that is caught up inside of another rock.
