Key bed

Key bed

​How do major geologic events help build Earth's time line?

​sometimes major events in Earth's history can leave a distinctive layer in the rock record.

Open Ended

What do you think happens to the ash from huge volcanic eruptions like Mount St. Helens?

Multiple Choice

The layer at the top?

• older than 540 mya

• younger than 540mya

• older than 730mya

• between 540 and 730mya

Multiple Choice

The layer at the bottom?

• older than 540 mya

• younger than 540mya

• older than 730mya

• between 540 and 730mya

Multiple Choice

The layer at the middle (brown)?

• older than 540 mya

• younger than 540mya

• older than 730mya

• between 540 and 730mya

​Scientists hypothesize that a meteorite impact might have caused the mass extinction that occurred when

​ evidence for this impact is in a clay layer containing the element iridium in rocks around the world.

​Iridium is rare in Earth rocks but common in meteorites.

Multiple Choice

Would you expect to find dinosaur fossils in undisturbed rocks that are above the iridium layer?

• yes

• no

​key bed

​A rock or sediment layer used as a marker and help geologists correlate rock formations in different geographic areas.

​

Multiple Select

Examples of key beds?

• ash from volcanic eruption

• igneous rock

• iridium from meteorite impact

• sedimentary rock