放射性测年法
解释放射性测年法的工作原理：放射性同位素以已知速率衰变（半衰期），因此测量岩石或化石中母体同位素与子体同位素的比例，可以得出绝对年龄；并区分碳-14（适用于约5万年以内）和铀-铅法（适用于数百万年到数十亿年）。
Explain how radiometric dating works — radioactive isotopes decay at a known rate (half-life), so measuring the ratio of parent to daughter isotope in a rock or fossil gives an absolute age; distinguish between carbon-14 (useful up to ~50,000 years) and uranium-lead (useful for millions to billions of years)
学习证据 / Evidence
- 将半衰期定义为一半放射性母体同位素衰变为子体同位素所需的时间
- 解释样本中母体与子体同位素的比例可用于估算绝对年龄
- 区分碳-14（用于较新的有机物质）与铀-铅或钾-氩法（用于深远的地质年代），并说明为什么碳-14不能用于恐龙骨骼
- Defines half-life as the time for half the radioactive parent isotope to decay to the daughter isotope
- Explains that the parent:daughter ratio in a sample gives an estimate of absolute age
- Distinguishes carbon-14 (for recent organic material) from uranium-lead or potassium-argon (for deep geological time), explaining why carbon-14 cannot be used for dinosaur bones
评估问题 / Assessment
如果 {{name}} 得知一块恐龙骨骼化石是用铀-铅放射性测年法测定年代的，他们能解释这意味着什么吗——是什么在衰变？为什么衰变速率很有用？以及为什么科学家大致不用碳-14来测定7000万年前的恐龙骨骼？
If {{name}} was told a dinosaur bone was dated using uranium-lead radiometric dating, could they explain what that means — what is decaying, why the rate of decay is useful, and roughly why scientists don't use carbon-14 for 70-million-year-old bones?