Geologic Time

Geologic time is very hard to understand. One way to wrap your mind around geological time is to put it into the perspective of a single year. At that rate, each hour of the year is equivalent to approximately 500,000 years, and each day is equivalent to 12.5 million years. If all of geological time is compressed down to a single year, Earth formed on January 1, and the first life forms showed up in late March. The first large life forms appeared on November 13, plants appeared on land around November 24, and amphibians on December 3. Reptiles appeared the first week of December and dinosaurs and early mammals came by December 13, but the dinosaurs, which survived for 160 million years, were gone by December 26. The Pleistocene Glaciation got started at around 6:30 p.m. on New Year’s Eve, and the last glacial ice left southern Canada by 11:59 p.m.As for people, the first to inhabit northern America got here about one minute before midnight, and the first Europeans arrived about two seconds before midnight(“Textbook Chapter 08 Geologic Time: GEOL-101-30382-2023SP”).

The San Andreas fault started moving about 28-30 million years ago and has horizontally slipped (transform motion) a total of about 186-220 mi(“Back to the Future on the San Andreas Fault | U.S. Geological Survey”). The way that the San Andreas fault is moving, Los Angeles will be a suburb of San Francisco in the future. 200 million years ago LA was in the middle of the Caribbean sea(HHMI). This is due to the movement of plate tectonics. Also a full day was 23 hours long. An awesome website to find more info is, https://media.hhmi.org/biointeractive/earthviewer_web/earthviewer.html

In the Cajon Pass some fossil plants and gastropods associated with bones and teeth of mammals that span the early Miocene Hemingfordian and Barstovian North American Land Mammal Ages (NALMA)(“Cajon Pass Geology”).

Below is a geologic time scale.