[Rebel_Ace]

"...Trees are a poor example because they can be observed..."

Trees are an excellent example. Trees are simply EASIER to observe than ATOMS, since trees are so big. You brought up OBSERVATION of Thorium decay. The implication was that no one has sat and watched a SINGLE Thorium atom decay, and as such, the figure for it's Half Life could not be trusted. No one has sat and watched a single tree grow for 4000 years either. The AGE of existing trees are INFERRED by observing OTHER TREES during their life cycle.

Similarly, the HALF LIFE of atomic isotopes is INFERRED by observing OTHER ATOMS during their life (decay) cycles. We don't watch ONE Thorium atom, we watch a ZILLION at once.

The PRINCIPLE is exactly the same.

There are MANY things that take longer than a human lifespan to complete. The orbit of Pluto for example. In fact, since it has been discovered, NO ONE has sat and watched Pluto completely orbit the Sun. Should I call into question the calculated orbital period?

[rjsimmon]

There are MANY things that take longer than a human lifespan to complete. The orbit of Pluto for example. In fact, since it has been discovered, NO ONE has sat and watched Pluto completely orbit the Sun. Should I call into question the calculated orbital period?

I understand orbital periods and the inference you are talking about, however, it does not answer the question of observation. The root of any scientific method is observation. At some point in time, observation occurred with trees and rings in order to postulate the theorem to derive the formula. Thorium dating is nothing more than SWAG.