in what type of rocks would geologists most likely find evidence of past life forms?; which is not an idea geologists use as they study earth?; relative dating methods help scientists to _____.; what principal involves an intrusive rock body younger than the rock into which it intrudes?; what determines the type of fossil that is formed; the laws of superposition and original horizontality are best applied to; according to the principle of cross-cutting relationships, an intrusive rock body is _____.; how are the numbers and ages of eras and other divisions of the geologic time scale determined?