russ_watters
Mentor
Have a look at the link. It's just algebra.

sophiecentaur
Gold Member
2020 Award
where should I begin
I think your problem is that you may need to begin a 'boringly long way' back in the process. The relationship between rate of emission from a sample and probability of a single nucleus decaying is, I would say, pretty sophisticated stuff - when approached without the back knowledge. But you can always just accept it, in the same way that you (and most of the rest of us) probably accept things like the Cosmological 'facts' we get bombarded with - such as how far it is to the nearest Galaxy and the age of the Universe.
But then there can be a problem coming to terms with how unsatisfactory that may be. Join the club.
One point I could make and that is that you can start at an elementary level and 'prove for yourself' some of the easier bits of Physics - like how levers work (quantitatively) and how confirming, a calculation of how much water you can heat up with your heating boiler etc. etc. . Eventually, you may find that you can 'believe' that other stuff can be predicted from theory, without actually knowing the theory. Note, I am not being patronising here; that statement is based on personal experience, which has allowed me to rely on what clever (creditable) people tell me. People who fail to do this end up as Climate Change Deniers and Creationists.

russ_watters
For the record, I am actually skeptical of deep time geology .
Hi dmehling,
I'm not a physicist, and I'm also way out of my league intellectually just visiting here, but I just completed a geology degree so I might be able to make a useful contribution to this thread. Absolute age of the earth is determined by zircons in volcanic ash beds and lava flows (rhyolitic through to andesitic geochemistry). Zircons (zirconium silicate) are isomorphic minerals which are lattices of silicate tetrahedra, which have gaps (between the clusters of tetrahedra) large enough to fit zirconium cations. They can also substitute uranium cations (hence isomorphic), but not lead cations, as leads ionic radius is too big (so any lead in the zircon is due to radioactive decay of the uranium). When this cools it reaches closure temperature, and radioactive decay begins. Another great thing about zircons is that they have a high melting point so are unlikely to be "reset" by metamorphic heating, and are incredibly durable and resistant to weathering. As you know there are several decay paths so the age of each zircon can be "cross-checked". There are other ways of absolute dating - in basalt flows - due to the rarity of zircons in mafic lavas, geologists use argon/argon in plagioclase or whole rock.
Which bit of that are you sceptical about?
Geology has a surfeit of other phenomena which can only be explained by deep time. Here's a couple off the top of my head: limestone (which forms on carbonate platforms under the sea), currently situated 5 km above sea level in New Guinea (and I'm talking entire mountain tops of the stuff - complete with marine fossils) - I'll leave it to you to ponder how long that process would take. Or magnetic striping in ocean floor basalts recording switching of polarity of the earths magnetic field, extending literally thousands of kilometres either side of the spreading ocean ridges capturing a continuous polarity reversal record for 180 million years, complete with age correlated fossils in the sediments above the bands.