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# The half-life of the uranium isotope $^{235} \mathrm{U}$ is 700 million years. The earth is approximately 4.5 billion years old. How much more $^{235} \mathrm{U}$ was there when the earth formed than there is today? Give your answer as the then-to-now ratio.

## $\frac{\left(N_{\mathrm{U}}\right)_{o}}{N_{\mathrm{U}}}=86.2$

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we have and Dig was and Lord have raise the bar off D over. Do you have so and not over and be comes out to be to race the part off the over Do you have equals to raise the bar off? We are looking at 4.5 Be the end years on behalf signed time is 700 million years or 0.7 1,000,000,000 years. So that comes out to be 86 0.1. So we have 86 times more. You 2 35 in the atmosphere.

Indian Institute of Technology Kharagpur