Dating techniques of the earth
This implies the earth is at least 20 million years old.
Astronomical cycles can also be used to measure relative age.
These estimates give 4.4-4.5 billion years for moon rock, and 4.54 billion years for iron metreorites.
For instance, measurable amounts of C-14 have been found in fossil material, such as coal (traditionally Carboniferous period c300 mya).
The earth precesses (wobbles like a spinning top) around the sun in a series of cycles.
These cycles affect sunlight and hence long-term can form layers in rock.
Mathematically, P = Po exp(-lambda T), where lambda = the decay constant and T = the period of decay. a zero initial number of D atoms, where P(or D) = the current number of P(or D) atoms, it follows that the age of a rock or mineral is computed as T=(1/lambda)ln(1 D/P).
Using radiometric techniques, the oldest dated minerals (4.0 - 4.2 billion years) are zircon crystals found in sedimentary rocks in western Australia.
Most people accept the current old-earth (OE) age estimate of around 4.6 billion years.