Scientists use radioactive isotopes such as carbon-14 or potassium-40 to date fossils. What is this method of dating fossils called?

3.1 Identify

• a) Fossil A: Trilobite
• b) Fossil B: Ammonite

3.2 Describe how these fossils may have formed in sedimentary rock.
These fossils formed when the organisms died and were rapidly buried by layers of sediment (like sand or mud) on the seafloor. Over time, the soft parts of the organisms decayed, but their hard shells were preserved. As more sediment accumulated, the layers compacted and cemented together, turning into sedimentary rock. Minerals from groundwater then seeped into the shells, replacing the original material or filling the empty spaces, thus forming a fossil.

3.3 Name TWO other ways that fossils are formed, other than in sedimentary rock.

• Preservation in amber: Organisms (often insects) are trapped in tree resin, which hardens over time into amber, preserving them.
• Freezing: Organisms are preserved in ice or permafrost, which prevents decay.
• Tar pits: Organisms become trapped in sticky tar, which preserves their remains.

3.4 Scientists use radioactive isotopes such as carbon-14 or potassium-40 to date fossils. What is this method of dating fossils called?
This method is called radiometric dating (or radioactive dating).