Original horizontality 2. Superposition - for undisturbed rock sequence, younger 3. Lateral continuity - rocks story on top 4. Cross-cutting relationships 5. Inclusions - included rock is older than the surrounding rock 6.
Uniformitarianism present is key to the past.
Physical continuity 2. Similarity of rock types - core should be take this 3. As neutron and proton leave, energy is release which can be detected with a Geiger counter or something similar With the lost of protons, the atom becomes a different element. Rate of decay is constant for most radioactive elements.