Analysis indicated that the age of the sample was 50 million years.

Like fossils, the chemical and physical characteristics of rocks, minerals, and organic materials can be used for correlation.

Selected examples of correlation geochronology methods used by USGS scientists include: Paleomagnetic Dating - Under certain conditions, a record of the orientation of the Earth's magnetic field is preserved in rocks and sediments.

Micropaleontologists and palynologists work with microscopes or scanning electron microscopes (SEM).

Paleontologists frequently work in conjunction with other scientists utilizing any number of other geochronology methods.

For more information, contact Andrei Sarna-Wojcicki. Strontium Geochronology - With modern isotope separation equipment, the content of selected elemental isotopes can now be measured in concentrations to parts-per-million to parts-per-billion and beyond.

The Sr geochronology method involves extracting these isotopes from fossil shell material (only several milligrams of sample are necessary for X-ray fluorescence spectroscopy).

Geologic research and mapping requires the determinations of the ages and composition of rocks.

A geologic map or report typically is only a summary of investigations that frequently involve the collecting and processing of hundreds of rock samples, followed by the evaluation and interpretation of data from a variety of analytical techniques.

In Menlo Park, contact: Dwayne Champion for more information about the paleomagnetic lab.