Geological Timeline

Geologic Time Data Collection

So cool.

Timelines

Timelines are a tool that can show the relative order in which these events happened, from the earliest to the most recent. Ands it can tell us the actual, or absolute date when each occurred.

Geologic Timeline

Learning about events and when they happened helps us piece together our biological history. We can see connections and major progressions in evolution and biodiversity.

Relative time is recorded in rocks

Each of these rock layers, or strata, represents a period of time in Earth's history, so the entire sequence of layers is another timeline.

This drawing makes the layers easier to see. Can you figure out the relative order in which the layers were formed? 

Let's figure out the relative strata- which strata is the oldest? Which one is the youngest?

Open Ended

Let's figure out the relative strata- which strata is the oldest? Which one is the youngest?

Law of Superposition

All over the world, rock layers are deposited on top of layers that were already there.

As more and more layers are deposited, the older rock layers end up at the bottom of the sequence and the newer ones toward the top. In geology, this is referred to as the Law of Superposition.

Applying the Law of Superposition

We can apply the Law of Superposition to the fossils as well as to the rocks. Which of the fossils is the earliest (oldest)?

Multiple Choice

Which fossil is the earliest (oldest)?

Radiometric dating gives absolute dates

We can tell that the brachiopods are older than ammonites and younger than trilobites, but how can we determine when they actually lived?

Radiometric Dating

This scientist is looking at the chemical composition of the rocks.

Since the chemical composition has changed through time at a certain rate, we can determine how old rocks are by analyzing their chemistry. This process is called radiometric dating.

Using radiometric dating allows us to find accurate ages for particular layers of rocks.

Radiometric Dating

How can we get an "absolute" date for the layer of rocks and fossils shown by the arrow?

Notice that the layer we are interested in is between two layers of volcanic ash.

Due to their chemical composition, volcanic ashes are easy to date.

More Radiometric Dating

Using radiometric dating, we get an age for the upper volcanic ash layer of 468 million years.

(mya = millions of years ago)

The lower one is 470 million years old.

Which would be the correct age range for the layer we are interested in?

Multiple Choice

• 470-472 million years

• 465-472 million years

• 465-467 million years

• 468-470 million years

You are so smart!

Great! Using the Law of Superposition, the layer on the bottom is older and the layer on top younger. So the ages of "our" layer is in-between these two. It is between 468 and 470 million years old.

Geologic Timescale

This is the Geologic Time Scale. It represents the entire natural history of the Earth.

It is broken up into several periods of time, where there were great changes in the biodiversity on Earth.

We can see distinct changes in the flora (plants) and fauna (animals of each time period.