Transcript Science Earth`s Changing Surface

Science
Earth’s Changing Surface
Chapter 4
Section 3
Radioactive Dating
• Everything around us is made up of matter
• Matter is made up of tiny particles called
atoms
• When atoms in a particular type of matter
are the same, the matter is an element
• There are about 110 elements
• Most elements are stable
• They do not change under normal
conditions
Continued
• Some elements exist in forms that are unstable
• These may break down or decay, & in the process
release particles & energy in a process called radioactive
decay
• These unstable elements are said to be radioactive
• During this decay, the atoms of one element break down
to form atoms of another element.
The Rate of Radioactive Decay
• As a radioactive element w/i the igneous rock decays, it
changes into another element.
• So, the composition of the rock changes slowly over time
• The amt of the radioactive element goes down, but the
amt of the new element goes up
• *the rate of decay of each radioactive element is
constant—it never changes.
• This rate of decay is the element’s half-life.
• This is the time it takes for half of the radioactive
atoms to deday
Absolute Ages from Radioactive Dating
• Geologists use radioactive dating to determine the
absolute ages of rocks.
• First, the amt of radioactive element in a rock is
determined
• Then a comparison this amt to the amt of the stable
element into which the radioactive element decays
• Types of dating
• Potassium-Argon Dating—used to date rocks
• Carbon-14—useful for dating plants & animals up to
50k years ago
Radioactive Dating of Rock Layers
• RA cannot be used in dating other than igneous rocks
• For sed rocks scientists date the intrusion & extrusions
nearby.
• E has been dated to about 4 billion years
• May be older