READ: Important Vocabulary Terms
READ: Important Vocabulary Terms
These are the most important vocabulary terms to learn this week. Please make sure you understand these terms.Fossils are the preserved remains or traces of organisms that lived in the past. The fossil record is the record of life that unfolded over four billion years and pieced back together through the analysis of fossils. Relative dating determines which of two fossils is older or younger than the other, but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower layers were laid down earlier, so they are assumed to contain older fossils. Absolute dating determines about how long ago a fossil organism lived. This gives the fossil an approximate age in years. Absolute dating is often based on the amount of carbon-14 or other radioactive element that remains in a fossil. A molecular clock uses DNA sequences to estimate relatedness among species. Molecular clocks estimate the time in geologic history when related species diverged from a common ancestor. Species that have greater differences in their DNA sequences are assumed to have diverged from their common ancestor in the more distant past. The geologic time scale divides Earth’s history into divisions (such as eons, eras, and periods) that are based on major changes in geology, climate, and the evolution of life.
