Geology Knowledge Challenges

Igneous rocks are made of crystals that grew as molten rock cooled.

Layers settle one on top of another, so the oldest is at the bottom (superposition).

Glaciers drop debris of every size together.

Sea creatures are fossilised in sediment laid down underwater; the rock was lifted up later.

Fossil corals show a honeycomb or branching pattern.

Sea water chills the lava’s surface instantly into rounded pillows.

Shells, bones, footprints and even microbial layers can be preserved as fossils.

This is one path around the rock cycle.

Oman’s Samail ophiolite is a slice of ancient ocean floor thrust onto Arabia.

This is the standard ophiolite sequence.

Garnet grows at very high pressure.

Slow cooling gives crystals time to grow.

Schist’s aligned minerals record heat and pressure.

Mats of microbes trapped sediment layer by layer.

Each rock records a different environment.

See each chapter on the Time Machine.

High-precision U–Pb dating of zircon gives about 96–95 million years.

In obduction ocean lithosphere rides up onto a continent; in subduction it sinks beneath.

Dating shows the sole and the igneous crust formed at about the same time.

High-pressure minerals such as garnet show deep burial in the Late Cretaceous.

New carbonate minerals and travertine form, a natural example of carbon capture.

Olivine forms olive-green glassy grains.