How Fossils Form

For ages 7–9, teach fossilisation as an ordered CAUSAL chain with conditions: (1) an organism dies; (2) it is RAPIDLY BURIED in sediment (mud/sand) — the make-or-break step, because exposed remains rot or are scavenged; (3) soft parts decay while hard parts (bone, teeth, shell) remain; (4) over millions of years minerals carried by groundwater seep into the hard remains, filling tiny spaces and often gradually replacing the original material, while the sediment compacts and hardens into rock, preserving the shape; (5) later uplift and erosion expose it. Burial is necessary but does not guarantee a fossil. Make RARITY explicit so children reason that most living things leave no fossil, seeding the big idea that the fossil record is an incomplete, lucky sample. Use correct vocabulary (sediment, minerals, rock, buried) in context. The strongest proposed activity is intended to let children choose settings, with quick burial decided by setting-dependent chance, and run time forward so that rarity may become an observed outcome rather than a stated fact; staged diagrams and ordering/check tasks support the sequence and vocabulary.

• 'Fossils are the original bone, unchanged' — minerals usually replace the remains; a fossil is rock in the shape of the original.
• 'Any dead animal becomes a fossil' — fossilisation is rare; most decay or are eaten before burial.
• 'Fossils form quickly' — mineral replacement and rock formation take (typically) millions of years.
• 'Soft parts fossilise as easily as bones' — usually only hard parts (bone, teeth, shell) survive; soft tissue rarely preserves.
• 'Fossils form on the surface where the animal died' — burial in sediment (often water-laid) is essential; surface remains are lost.

• A staged cross-section: dead animal on a riverbed → layers of sediment pile on → minerals replace bone → rock with fossil → erosion exposes it.
• A timeline slider showing 'millions of years' compressing the mineralisation step.
• A 'fossil or lost?' branching diagram: buried quickly → fossil; left exposed → rots/scavenged → no fossil.
• Soft-parts-vs-hard-parts labelling on an organism.

• Teach it as a conditional CAUSAL chain (each step enables the next), foregrounding rapid burial as the make-or-break step.
• Make rarity explicit — have children reason that most animals rot or are eaten, so only a tiny fraction fossilise; this seeds 'the fossil record is incomplete'.
• Distinguish soft parts (usually lost) from hard parts (bone, teeth, shell) that typically fossilise, explaining why we mostly find skeletons.
• Insist on correct vocabulary (sediment, minerals, rock, buried) used in context, per Y3 'Rocks'.
• Use a compare-conditions approach (buried fast vs left exposed) so the necessity of burial is discovered, not asserted.