The difference in time between the youngest of the Proterozoic rocks and the oldest of the Paleozoic rocks is close to 300 million years.

Tilting and erosion of the older rocks took place during this time, and if there was any deposition going on in this area, the evidence of it is now gone.

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Learn about different types of radiometric dating, such as carbon dating.

Understand how decay and half life work to enable radiometric dating.

Figure 8.6a A xenolith of diorite incorporated into a basalt lava flow, Mauna Kea volcano, Hawaii.

The lava flow took place some time after the diorite cooled, was uplifted, and then eroded.

Fossils, by definition, are the remains or traces of organisms that lived at least 10,000 years ago.

This date marks the end of the Cenozoic Era and the Pleistocene Period on the geologic time scale.

The flat-lying rocks at the top are Paleozoic (540 to 250 Ma).

The boundary between the two represents a time gap of nearly 300 million years.

Figure 8.8 The great angular unconformity in the Grand Canyon, Arizona.

The tilted rocks at the bottom are part of the Proterozoic Grand Canyon Group (aged 825 to 1,250 Ma).

Composed of layers of sediments laid down by colonies of cyanobacteria, stromatolites still exist, but are quite rare today.