Background Knowledge:

Geologists use chemistry to examine rocks that formed in ancient oceans, revealing details about the history of life on Earth, such as the environmental conditions during the Late Devonian.

Methods that analyze the types of minerals found in the rocks and how they changed over time, provide clues about oxygen levels in the atmosphere, climate changes, and other disruptions associated with mass extinctions. These techniques help reconstruct the story of Earth's ancient ecosystems and catastrophic extinction events.

Watch the video to learn more! ->

A micrograph showing two framboid clusters in a rock sample

Framboid Clues

One special chemical clue comes from tiny, raspberry-shaped mineral clusters called framboids (their name even comes from the French word for raspberry, framboise). Framboids form when iron and sulfur mix in low-oxygen environments, like the deep ocean during a mass extinction. By studying the size and shape of framboids in rocks, scientists can figure out how much oxygen was in ancient oceans and what that might mean for life at the time.

Learn to read these "mineral time capsules" clues:

What do framboids tell us about the ocean environment from which a sample came?

NO FRAMBOIDS in the sample- probably came from a high oxygen environment
SMALL FRAMBOIDS (0-15 micrometers)- Anoxic (no oxygen) environment
BIG FRAMBOIDS (10-25 micrometers)- Some oxygen but probably not much

Work the Case:

Help the investigators determine whether the samples shown in the micrographs came from a high oxygen environment, low oxygen environment or anoxic (no oxygen) environment.

If needed, you can use a piece of scrap paper against the screen to mark what a length of 10 micrometers (µm) is (using the yellow lines on the diagrams), then use that measurement to determine the size of the different framboids shown.

Based on your analysis of the micrographs, which two of the samples show evidence of a once anoxic ocean environment?

Hint: Look at the micrographs and determine which one(s) indicate the lowest low oxygen conditions.

Now let's practice your graph interpretation skills. Study the graph below and report back to the investigators on what you learned from the data about the oxygen level in the ancient oceans this rock sample came from.

This about these two questions...

Is the graph below showing that there were many or few small framboids that are less than 10 micrometers?
Does this indicate high or low levels of oxygen?

Page updated

Report abuse