Discovery Education Science P4: Term 2, Unit 4, pp. 149–162
GoalWrite a scientific explanation of how canyons form, with a claim, evidence from our investigations and reasoning.
New words
explanation · a statement that tells how or why something happens, with evidencepattern · something that happens again and again in the same waylandscape · the land we see in a place
Explanation
Our big question is: How are canyons formed? Let us answer it like scientists. First, think about patterns. Canyons are deep and narrow, they often have a river at the bottom, and their walls show layers. Next, look at our evidence. In the stream tray, faster water cut a deeper channel. On the slope, steeper ground gave more erosion. In the jar, sediment settled in layers. Chalk in vinegar showed that rock can be eaten away. Then write the reasoning: a river erodes rock, carries the pieces away and drops them elsewhere. Because this goes on for millions of years, the river cuts a deep, steep-sided path and the layers in the walls are uncovered. Our claim can be: canyons form when moving water weathers and erodes rock over millions of years.
Claim
Evidence
Reasoning
canyons form when moving water erodes rock for millions of years
faster water cut a deeper channel; steeper slopes eroded more
a river carries rock pieces away, so over a long time it digs deep with steep walls
Worked examples
Activity
What it showed
stream tray
fast water cuts deeper
slope test
steeper ground erodes more
settling jar
pieces settle in layers
Gathering evidence. Marwan lists what each activity showed. Tray: fast water cuts deeper. Slope: steeper ground erodes more. Jar: pieces settle in layers. He writes next to each one how it supports the canyon claim.
Clue
What it suggests
stripes in the walls
layers laid down at different times
V-shaped cut
river cutting downward
wide floor
widened over a long time
Canyon clues. A canyon with red and white stripes has layers of different rock or sediment, put down at different times. A canyon with a V shape has been cut downward by a river. A canyon with a wide floor has been widened over time.
claim answers the question→evidence seen or measured→reasoning joins them
Does the claim fit? Jana asks three questions. Does my claim answer the question? Is each piece of evidence something we saw or measured? Does my reasoning explain why the evidence supports the claim? If one answer is no, she improves her explanation.
Class activity
Write it up. Use the table to write your own explanation of how a canyon forms. Begin with the claim in one sentence. Add two pieces of evidence from our investigations (the stream tray, the slope, the settling jar or the chalk). End with a sentence of reasoning. Read it to someone at home and ask: can you see why the evidence supports my claim?
Practice
1
Write a claim that answers “How are canyons formed?”
Canyons form when moving water erodes rock over millions of years.
2
Name one piece of evidence from our investigations.
For example: faster water cut a deeper channel in the stream tray.
3
What do stripes in a canyon wall tell us?
The wall is made of layers of rock or sediment laid down at different times.
