• Quick retrieval from earlier learning (How fossils form). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. In how a sea shell becomes a fossil, what happens straight after "layers of sediment cover it"? (the fossil is found in the rock millions of years later / a sea creature dies / the sediment slowly turns into rock / its shell sinks to the sea floor) → the sediment slowly turns into rockPrompt: Fossils form very slowly, buried in rock.
2. Why do most fossils show bones, teeth and shells rather than skin? (Animals had no skin / Hard parts last longer; soft parts rot quickly / Scientists remove the skin / Skin turns into rock straight away) → Hard parts last longer; soft parts rot quicklyPrompt: Which parts of an animal rot first?
3. In how a sea shell becomes a fossil, what happens straight after "the sediment slowly turns into rock"? (a sea creature dies / the fossil is found in the rock millions of years later / its shell sinks to the sea floor / layers of sediment cover it) → the fossil is found in the rock millions of years laterPrompt: Fossils form very slowly, buried in rock.

• Pass round different rocks and ask how each one might have formed.
• Share the objective: Rock layers: reading time from the bottom up. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: At the bottom of a lake, mud builds up about 2 cm every 100 years. A layer of mud is 22 cm thick. About how many years did it take to form?
• Step 1: 22 ÷ 2 = 11
• Step 2: 11 × 100 = 1100
• Step 3: So the answer is: 1100
• Answer: 1100
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. At the bottom of a lake, mud builds up about 5 cm every 100 years. A layer of mud is 20 cm thick. About how many years did it take to form? → 400Prompt: How many groups of 5 cm are in 20 cm?
2. Why might an old layer be found ABOVE a younger one? (Earth movements folded or flipped the layers. / Someone carried it there. / Old layers float. / The bottom layer is always youngest.) → Earth movements folded or flipped the layers.Prompt: Mountains can bend rock.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A rock layer contains rounded pebbles and fossil river snails. What was the environment when it formed? (a glacier / a river / the deep ocean floor / a desert with no water) → a riverPrompt: What rounds pebbles, and where do these snails live?
2. At the bottom of a lake, mud builds up about 2 cm every 100 years. A layer of mud is 22 cm thick. About how many years did it take to form? → 1100Prompt: How many groups of 2 cm are in 22 cm?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-4.