In 2011, the United Nations announced that the human population reached 7 billion and was increasing at approximately \(1.5 \%\). Estimate the doubling time of the human population and then estimate the available land area on Earth per person at the end of the first and the third doubling times. The Earth is approximately two-thirds water and can be approximated as a sphere of \(8000 \mathrm{mi}\) in diameter. Then, discuss the implications for these estimates.