Cosmic-ray exposure dating can be used to estimate the length of time a rock surface has been exposed to the atmosphere. When cosmic rays strike quartz minerals at Earth's surface, they produce the rare isotope helium-3 (3He^{3}\text{He}3He) at a nearly constant rate. The greater the concentration of 3He^{3}\text{He}3He, the longer the rock has been exposed.
The graph below represents the line of best fit for the concentration of 3He^{3}\text{He}3He in quartz samples plotted against their exposure age (in thousands of years).
Calculate the rate of 3He^{3}\text{He}3He accumulation using the line of best fit shown in the graph. Give your answer to three significant figures.
The production rate of 3He^{3}\text{He}3He in quartz can vary by as much as 12% depending on the altitude and geomagnetic latitude of the site. Use the graph to calculate the estimated exposure age of a moraine sample (where the 3He^{3}\text{He}3He concentration is 4.6×106 atoms g−14.6 \times 10^6\text{ atoms g}^{-1}4.6×106 atoms g−1), and the range over which this estimate may vary.
