BIO 111 Chapter 41, 18: 2-13 (41.4, ch. 18)
Document Summary
18. 1 eve(cid:374)t i(cid:374) earth"s history ca(cid:374) be dated. Although some things evolution can be tracked, most things happen very slowly and must be thought of as taking millions of years in conditions that are different from modern ones. Fossils of similar organisms are found in widely separated places on earth. Certain fossils are always found in younger strata, and certain other fossils are always found in older strata. Organisms found in younger strata are more similar to modern organisms than are those found in older strata. Radioisotopes provide a way to date rocks: half-life the specific time interval at which half the atoms in a radioisotope become a different, stable isotope. Is used for radiometric dating the ability to use half-life to date fossils and rocks. Radiometric dating methods have been expanded and refined: for rocks older than 60,000 years it is hard to do radiometric dating simply using the half-life.
