Use Figure 7.11 to find the isotope with the greatest heat production (a) 4.5 billion year...

Use Figure 7.11 to find the isotope with the greatest heat production (a) 4.5 billion years ago, and (b) 2 billion years ago.

FIGURE 7.11 The Rate of Energy Released as Heat by Radioactive Isotopes of Aluminum, Potassium, and Uranium During the Last 4.5 Billion Years Notice that the rates of energy released by 40K and 235U have declined considerably over the past 4.5 billion years. 238U has declined relatively little because of its long half-life. 26Al, because of its short (700,000 year) half-life, may have been a very important source of energy shortly after the solar system formed, but it is nearly absent from the solar system today.