Changes

== Principles ==

== Principles ==

No method exists for ''measuring'' time, except by measuring it as it is passing.   

No method exists for ''measuring'' [[time]], except by measuring it as it is passing.   

Therefore, the age of an artifact must be ''calculated''.  

Therefore, the age of an artifact must be ''calculated''.  

The basic principle in any dating method is to find a process that is occurring at measurable rate and which is causing a change, measure the rate of that process, work out what state the artifact was in at the beginning of the process, observe what state it is in now, and to calculate how long the process at the measured rate would need to occur to effect that change.

The basic principle in any dating method is to find a process that is occurring at a measurable rate and which is causing a change, measure the rate of that process, work out what state the artifact was in at the beginning of the process, observe what state it is in now, and to calculate how long the process at the measured rate would need to occur to effect that change.

For example, to work out how long a candle has been burning, the following steps would be needed:

For example, to work out how long a [[candle]] has been burning, the following steps would be needed:

# Measure how long it takes the candle to burn down a given amount.

# Measure how long it takes the candle to burn down a given amount.

# Find out how long the candle was when it started burning.

# Find out how long the candle was when it started burning.

# Calculate how long it would need to burn in order to burn that length.

# Calculate how long it would need to burn in order to burn that length.

For most radiometric dating methods, one radioactive element changes by a process of nuclear decay into another element (often through a number of intermediate steps.  For example, uranium will eventually decay into lead.  So to measure how old a specimen containing some uranium and some lead is, the following steps are required:

For most radiometric dating methods, one radioactive element changes by a process of nuclear decay into another element (often through a number of intermediate steps).  For example, [[uranium]] will eventually decay into [[lead]].  So to measure how old a specimen containing some uranium and some lead is, the following steps are required:

# Measure the decay rate of uranium.

# Measure the decay rate of uranium.

# Find out how much uranium was in the specimen to start with (this might be done by assuming that all the lead was originally uranium).

# Find out how much uranium was in the specimen to start with (this might be done by assuming that all the lead was originally uranium).