Geological Time Chapter 4 Section 3 / 4 Radioactive Dating / Geologic Time Scale
Carbon-14 can be used to date plants and animals as old as _______________ .
50,000 years ago
As a radioactive element within the igneous rock decays, the amount of the radioactive element goes ____________, but the amount of the new element goes _________ .
down up
After Precambrian Time the basic units of geologic time scale are ______ and ________ .
eras periods
What types of fossils would carbon-14 be used to date?
frozen mammoths, wood, bones, skeletons of prehistoric humans Carbon-14 is useful to date materials from plants and animals that lived up to 50,000 years ago.
Because the time span of Earth's past is SO GREAT, geologists use the _______________ to show Earth's history.
geological time scale
The rate of decay is the element's _________ .
half-life
What type of rocks is radioactive dating used for?
igneous rocks
The "birthday" of an igneous rock is when ___________ .
it hardens to become a rock
Each era is divided into ___________ .
periods
Scientist use ___________ to date ancient rocks because it has a long half-life.
potassium-40
What are two types of radioactive dating?
potassium-argon dating (potassium-40) carbon-14 dating
What method do geologists use to determine the absolute age of a rock?
radioactive dating
Igneous rocks have naturally occurring __________in them.
radioactive elements
__________________ covers about 88% of the Earth's history.
Precambrian Time
A geologist finds a fossil in a layer of sedimentary rock between two igneous extrusions. What could you say about the age of this fossil?
Radioactive dating would be used to determine the age of the two extrusions because radioactive material occurs naturally in igneous rocks. The age of the sedimentary rock with the fossil in it would be in between the two ages of the igneous extrusions.
In radioactive dating, scientist 1.____________ then 2. __________________.
1. First determine the amount of a radioactive element in a rock. 2. Compare that amount with the amount of the stable element into which the radioactive element decays.
In which type of rock can scientists determine absolute age? Explain.
Igneous rock Radioactive elements occur naturally in igneous rock.
Does carbon-14 dating work for sedimentary rocks? Why or why not?
No Sedimentary rocks are made up of bits of other rocks of all ages. Radioactive dating would be the age of all the particles of rocks that make up sedimentary rock.
Can radioactive dating be used on sedimentary rocks? Explain.
No Sedimentary rocks are made up of particles of rocks of all different ages. Radioactive dating would be giving the age of the particles not the sedimentary rock.
Would you use carbon-14 to date a rock that may be several million years old? Explain.
No. Carbon-14 has a short half-life of only 5, 730 years. After millions of years the amount of carbon 14 left would be so small you couldn't detect it.
How is the age of sedimentary rock determined?
Scientist use the age of igneous extrusions and intrusions to determine the age of sedimentary rock
How was the geological time scale first developed by scientist?
Scientists studied rock layers and index fossils worldwide, and placed Earth's rocks in order by relative age. Then they used radioactive dating to determine the absolute age of the divisions in the geological time scale.
Why is it difficult to determine the absolute age of sedimentary rock?
Sedimentary rock is made up of particles of many other rocks of different ages.
How does the composition of a rock containing a radioactive element change over time?
The amount of the radioactive element decreases as the amount of the new element increases.
What is radioactive decay?
The process where atoms in an element break down and form another element.
How is a radioactive element's rate of decay like a ticking clock?
The rate of decay is constant, just like the constant, even ticking of the clock.
Geological time scale is ________________ .
a record of life forms and geologic events in Earth's history.
Geologist use radioactive dating to determine the _________ ages of rocks.
absolute
All matter is made of ________. When all the atoms in matter are the same, the matter is an ____ . There are over _____ known elements.
atoms element 110
______ is added to the tissues of plants and animals as they grow. No more carbon is added after they ______ .
carbon die
Carbon-14 is a radioactive form of ________ . All _________ and _________ contain carbon including some _____________ .
carbon plants and animals carbon-14
After an organism dies, the ___________ begins to decay. Scientist measure the amount of carbon-14 left in the organism's remains to determine its _______ age.
carbon-14 absolute
Major ____________________ mark where one unit of time ends and the next one begins.
changes in life forms
The rate of decay of each radioactive element is ____________ . This rate of decay ___________ .
constant never changes
The age of igneous rocks can be determined by the rate at which these radioactive elements ________.
decay
Most elements are _____ and don't change under normal conditions.
stable
The half-life of a radioactive element is ______________________ .
the amount of time it takes for half of the radioactive atoms to decay
During radioactive decay, ___________________ .
the atoms of one element break down to form atoms of another element
After Precambrian Time there are divided into _______ long units of time called ________ .
three eras
Some elements are _______ and over time as they decay or break down they release particles and energy in a process called ______________ . These types of elements are _______________ .
unstable radioactive decay radioactive
