This process lead to a system of time containing eons, eras, periods, and epochs all determined by their position in the rock record.
For example, rocks of the Phanerozoic eon are found on top of rocks from the Proterozoic eons therefore rocks of the Phanerozoic are younger than rocks of the Proterozoic.
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This means that a quartz sandstone deposited 500 million years ago will look very similar to a quartz sandstone deposited 50 years ago.
Making this processes even more difficult is the fact that due to plate tectonics some rock layers have been uplifted into mountains and eroded while others have subsided to form basins and be buried by younger sediments.
The most obvious feature of sedimentary rock is its layering.
This feature is produced by changes in deposition over time.
When an isotope emits an alpha particle, the resultant daughter product has an atomic number two units less than its parent's atomic number, and an atomic weight four units less than its parent's atomic weight.
When an isotope emits a beta particle, it decays to a daughter with an atomic number one unit greater and an essentially unchanged atomic weight.
After another half-life, 25 units of the parent isotope will remain, and 75 units of the daughter product will have been produced.
After another half-life, 12.5 units of the parent isotope will remain, and 87.5 units of the daughter product will have been produced.
Beta particles originate in the nucleus, presumably by breakdown of a neutron into its proton-electron components.