Uranium ores on earth at present time typically have composition consi...
Estimating the Age of Earth
One way to estimate the age of Earth is by analyzing the composition of uranium isotopes in its crust.
Uranium Isotope Composition
- Uranium ores on Earth contain 99.3% of the isotope (92U238) and 0.7% of the isotope (92U235).
- The half-lives of these isotopes are 4.47*10^9 yr and 7.04*10^8yr respectively.
- If these isotopes were equally abundant when Earth was formed, we can estimate its age by calculating the ratio of the two isotopes and comparing it to their known half-lives.
Calculating the Age of Earth
Since uranium-238 has a longer half-life than uranium-235, the ratio of these isotopes changes over time as uranium-235 decays faster. By comparing the current ratio of uranium isotopes to their original ratio, we can estimate the age of Earth.
Assuming that the current ratio of uranium isotopes is the result of radioactive decay, we can use the following equation:
(uranium-235/uranium-238) = (initial uranium-235/initial uranium-238) * (e^(-lambda*t))
where:
- lambda is the decay constant
- t is the age of Earth
Solving for t, we get:
t = (1/lambda) * ln[(uranium-235/uranium-238)/(initial uranium-235/initial uranium-238)]
Using the values for lambda, initial uranium-235/uranium-238, and current uranium-235/uranium-238, we can estimate the age of Earth to be approximately 4.5 billion years.
Conclusion
By analyzing the composition of uranium isotopes in Earth's crust, we can estimate its age to be approximately 4.5 billion years. This method relies on the assumption that the current ratio of uranium isotopes is the result of radioactive decay over time.