Geological Dating -Determining rock strata by geological composition The geologic time scale is a way that scientists work to understand the timespan of our planet based on empirical and fossil-based evidence. This evidence is then used to try and place events in Earth’s history. Many things on our planet, such as the formation of mountains, or the draining of lakes by rivers, take millions of years. The creation of life on earth and the extinction of life on earth has happened many times over. Scientists have documented at least 5 mass extinctions. Geological Dating -Determining rock strata by geological composition -Using depth to determine relative age -Predicting natural events by strata

What is Geological Dating? It is how scientists can determine the relative age of rocks and fossils. They do this by looking at the strata (layers) of the rock.

Relative Age-Quick Practice Look at the image below…what is the oldest rock layer? The youngest?

Relative Age-Quick Practice Limestone is the oldest layer. Sandstone is the youngest layer.

Relative Age-Quick Practice Sometimes the picture is not so clear… Can you predict what happened? Think about your knowledge of plate boundaries… Transform Boundary Hot Spot

Understanding Geologic Time To better understand dating you must take a closer look at the theoretical timeline.

Fossils Fossils are the remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock.

What is the significance? In understanding the time period that different species roamed the Earth we can predict and draw conclusions to determine the relative age of rocks and ultimately, better understand planet Earth’s past.

Predicting Past Events How can you explain what you are observing?

Predicting Past Events How can you explain what you are observing?

Predicting Past Events How can you explain what you are observing?

Blow your mind… It is interesting to note: Something like 1:1000 species actually fossilizes. Let me phrase this again to emphasize: Not 1 in 1000 individuals, but 1 in 1000 species actually end up forming fossils. Thus, there are many species that lived and died on earth not captured at all in our lithographic record of life. Secondly, as a result of this, a bulk sum of the fossil record is blank. We are missing huge chapters of life on Earth, as dying and decaying organisms either (a) didn’t exist at that time or (b) the conditions were not right for fossilization. New fossil evidence is discovered all of the time which can greatly change the way we perceive these biological-relationships on earth.