He studied the fossils' age and how tall the mountains are. He also studied how old they are. I don't know about Coal Beds but he also used balloons to find out the continents were once a big supercontinent called Pangaea and they apparantly drifted apart
It allowed them fewer ships than the US and Britain limiting the kind of parity they hoped to have on the world stage in terms of naval power.
One of the arguments went that the US and Britain had to have larger navies because of their need to maintain a force in more than one operating theater while the Japanese only had to worry about their side of the Pacific. It wasn't something that made a number of hardcore military types within the Japanese leadership very happy, but they ended up signing the treaty anyway (though refused to renew it in the 1930s).
I think this is the correct answer, but let me know if it is incorrect. People were having more children per family.
