How Long Ago Did the Supernova Occur That Created Earth's Heavy Elements?

[cdymdcool]

All the very heavy atoms found in the Earth were created long ago by nuclear fusion reactions in a supernova, an exploding star. The debris spewed out by the supernova later coalesced to form the sun and the planets of our solar system. Nuclear physics suggests that the uranium isotopes 235U (half life=7.04*10^8 yr) and 238U (half life=4.47*10^9 yr) should have been created in roughly equal amount. Today, 98.6% of Uranium is 238U and 1.4% is 235U. Long many years ago did the supernova occur?



The exponentiallly decay formula?



This is not something that I've seen before...

 

[nickjer]

You should at least write out the decay formula. Then write two separate equations for each isotope and solve for the time. We can guide you along the way, but you need to start the work and show your steps.