Paleomagnetism relative dating
These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species.The age of the fossil must be determined so it can be compared to other fossil species from the same time period.Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.The geomagnetic field changes on frequencies of 10s of microseconds (radio waves) to millions and perhaps billions of years.Direct observations contribute to our knowledge of field behavior for the last few centuries, but on longer times scales we need to use paleomagnetic and archaeomagnetic techniques.
Then we will turn to what we can glean from accidental records made by archaeological and geological materials.
The following introduces some of the reasons for studying the geomagnetic field.
To answer some of the questions just raised, we need measurements of the geomagnetic field.
Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.
Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.
New dating methods are invented all the time, however, most have practical limitations.