1. The age of the Earth is about 4.543 x 10" years. When the Earth formed, a certain radioisotope with a half-life of 1.05 x 10* years was created.If the radioisotope stated as 250 mg, how much would remain since the Earth's formation? [3 marks] 2. Tritium, a by-product of the CANDU nuclear power reactor, has a half life of 12.3 years. How much time is required for its radioactivity to reach one-quarter of its original level? [3 marks]