half-life
the time it takes for half of the atoms of a radioactive element to decay; the rate of decay of each radioactive element never changes.
isotope
atoms of the same element that have different numbers of neutrons
radioactive
When an atom's nucleus is unstable and will emit energy or particles in an attempt to become more stable.
radioactive decay
the process in which radioactive elements break down; the radioactive elements break down to form another element
What three (3) key points occur during radioactive decay?
During radioactive decay: 1) elements (radioactive isotopes - parent) break down, 2) releasing particles or energy, 3) forms stable elements - daighter) forms
_____ is 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
What is the approximate half-life of carbon-14?
roughly 5,700 years
The time it takes for _____ the number of radioactive atoms to decay is the _____ of the element.
half; half-life
If a substance has a half-life of one year, how long will it take for half of the substance to decay?
1 year
How does the penny model (tails -parent material - no decay; heads -daughter material - decay) compare to half-life?
half-life - time it takes for half (1/2) the number of radioactive atoms to decay; during each trial, approximately 50% (1/2) of the pennies will land on (TAILS -parent material - no decay); and 50% (1/2) of the pennies will land on (HEADS -daughter mater
An intrusion is always _____ than the rock it cuts through.
younger
Can geologists use radioactive dating to find the absolute ages of sedimentary layers A, B, C, D, and E? Why?
Radioactive dating is used ONLY on igneous rock; RD would NOT work on sedimentary layers (A,B,C,D, E); sedimentary rocks are made of particles from other rocks so RD can give ages of particles, not the rock itself.
Can geologists use radioactive dating to find the absolute ages of the extrusion or the intrusion? Why?
Geologists can use radioactive dating because EXTRUSIONS and INTRUSIONS are made of igneous rock.
What is the relative age of rock layer C? Explain.
Rock layer C is at least 80 million years old; able to identify its relative age because age of intrusion (cuts-partway-across) is known. AN INTRUSION IS ALWAYS YOUNGER THAN THE ROCK IT CUTS THROUGH.
Explain the natural process on which radioactive dating is based.
Radioactive dating is based on the concept of radioactive decay; atoms of one element break down to form the elements of another element.
During a natural process called_____, the atoms of one element break down to form atoms of another element.
radioactive decay
The time it takes for half of the atoms in a sample of a radioactive element to decay is called the element's _____.
half-life
Why are Half-lives of elements useful in radioactive dating?
Each element has a constant and measurable half-life; these references are used to help calculate the absolute age of rocks and fossils.
Which element do living organisms constantly exchange with the atmosphere?
Carbon
List two (2) elements used in radioactive dating.
1) potassium -40, and 2) Carbon-14
Why is Potassium-40 useful in radioactive dating?
1) Potassium-40 has a long half-life, 2) which is useful in dating the most ancient rocks
All plants and animals contain some _____.
Carbon -14
Why is Carbon -14 useful in radioactive dating?
1) All plants and animals contain some Carbon -14 that decays after the organism dies, 2) measure amounts of carbon-14 to determine age of the organism
One Carbon-14 dating activity estimated 5,700 years, and another Carbon-14 dating activity estimated 5,730 years; why the difference?
Both values are estimates; 5,700 is the estimated value with two significant figures, and 5,730 is the estimated value to three significant figures (measure of error - give or take 40 years).
What is radioactive dating?
Geologists use radioactive dating to determine the absolute ages of rocks.
How does radioactive dating work?
Radioactive elements (igneous rocks) decay over time into other elements; this slowly changes composition of the rock.
How do scientists measure radioactive elements?
1) measure amount of radioactive (parent) element in a rock, 2) measure amount of the (daughter) stable element (AFTER the radioactive element decays), 3) then compare amount of parent/daughter elements, 4) calculate age of the rock using that information