Life Changed Over Time

Activities to try

1. 1

   Order the fossils and trace a feature changing through a rock column

   Why it works: 'Life has changed over time' is not just a story we are told — it is a pattern we can read from time-ordered rock layers. In well-documented lineages such as the horse, a series of separate fossils shows a feature changing in small steps over many generations, even though the record has gaps and does not preserve every generation.

   1. Sort a jumbled set of fossils into the rock layers where they belong, oldest at the bottom and youngest at the top (true for undisturbed layers, as in this model column); check each placement against the strata.
   2. Describe what you notice: the deep/older layers hold strange, often unfamiliar (now-extinct) creatures while the shallow/younger layers hold forms more like today's animals.
   3. Focus on one lineage (e.g. the horse) and move a time-slider from older to younger fossils, watching a feature change step by step across many fossils that span many generations: several toes (early horses had four on the front feet and three on the back) reducing toward a single hoof, body size generally increasing, teeth becoming taller-crowned for grazing. Treat the slider as a simplified model of one path through a branching horse family tree over deep time — not one animal transforming as it ages, and not a straight ladder of direct ancestors.
   4. State in your own words whether the feature changes suddenly (a jump) or gradually across the sequence, and give your evidence from the layers.
2. 2

   Compare an ancestral fossil with its living relative

   Why it works: Comparing a fossil with a living relative reveals both change and continuity, so we can describe specifically what altered over time rather than treating the fossil as an unrelated, random animal.

   1. Place the oldest fossil of a lineage beside its modern living relative (e.g. an ancient horse beside today's horse).
   2. Name at least one feature that CHANGED between them (e.g. number of toes, overall size, tooth shape).
   3. Name at least one feature that was RETAINED or is still recognisably similar.
   4. Write one sentence explaining how this comparison shows that life has changed over time while lineages still show continuity.
3. 3

   Explain how we know, and whose change it was

   Why it works: Change occurs across populations over many generations and across millions of years — not within a single individual's lifetime and not over just a few thousand years; fossils are the evidence for forms that no longer exist.

   1. Using a fossil sequence and a living relative, explain in a few sentences how we know life has changed over time.
   2. Answer: did the change happen to one individual horse during its own life, or across many generations of horses? Justify with evidence.
   3. Estimate the timescale of a change like the horse lineage: thousands of years, or millions of years? Explain why the fossil record points to deep time.
   4. State what fossils let us see that we could never learn from living horses alone.