Angela's Tools · Chapter 8 · Investigating Rock Strata
Worksheet 2 of 10
Rules, Features and Clocks: Sorting the Language of Strata
Learning target: I can sort the vocabulary of rock strata into rules, features and methods, choose the right rule for a new situation, and use the terms correctly in my own sentences.
Vocabulary in actionAbout 35 minIndividual
MS-ESS1-4 · supports
independent practicewritingdiscussion
NameDatePeriod
Directions
Read the twelve definitions first; they are written in plain words and you may look back at them at any time. Part A asks you to sort the terms into three bins. Part B gives short field situations; name the one rule or method that fits each. Part C completes a concept map. Part D asks you to tell similar terms apart, and Part E asks you to use the terms on something that is not a rock at all. Work alone, then compare Part B with a partner before moving on.
You will need: This worksheet, Pencil, Colored pencils for Part E (optional)
The terms
- strata
- Layers of rock, usually sedimentary rock. One layer is a stratum.
- relative dating
- Figuring out the order in which rocks formed and events happened (first, next, last) without giving ages in years.
- absolute dating
- Estimating how many years ago a rock formed or an event happened; for igneous rock this is done by measuring radioactive atoms and what they have decayed into.
- law of superposition
- In a stack of layers that has not been overturned or disturbed, each layer is younger than the one below it, so the bottom layer is the oldest.
- principle of original horizontality
- Gravity makes sediment settle into flat or nearly flat layers, so layers that are now steeply tilted or folded were bent after they formed.
- principle of lateral continuity
- A layer of sediment spreads sideways until something stops it or it thins out, so matching layers on two sides of a gap were once one continuous layer.
- law of cross-cutting relationships
- Anything that cuts across rock, such as an intrusion, a fault or a worn-down surface, must be younger than whatever it cuts through, because that rock had to exist first.
- intrusion
- A body of igneous rock that formed when magma pushed into cracks or weak spots in existing rock and then cooled. A thin sheet-shaped intrusion is called a dike.
- fault
- A break in rock along which the rock on the two sides has moved, so layers no longer line up.
- law of fossil succession
- Fossil species appear in rock layers in the same order everywhere on Earth, because life changed over time in one sequence.
- index fossil
- A fossil of a species that lived for a short span of geologic time, spread over a wide area, and is easy to recognize, which makes it a good marker for matching layers of about the same age.
- half-life
- The time needed for half of a sample's radioactive atoms to decay into a different kind of atom; each half-life halves what is left.
Part A: Three bins
1.Every term above belongs in exactly one bin. Write each term in its bin. (Hint: five terms are rules, four are things you can point to in rock, and three are methods or numbers that come from a method.)4 pts
| Bin | Terms that belong here |
|---|
| A rule geologists use to put events in order | |
| A thing you can see or point to in the rock | |
| A method, or a number that comes from a method | |
Part B: Which rule or method fits?
For each field situation, write the one term from the list that a geologist would use, and finish the sentence with what it lets the geologist conclude.
2.A dark band of hardened magma, one meter wide, cuts straight across three sandstone layers. Term: ______. So the geologist concludes that ______.1 pt
3.On both sides of a dry streambed, the same pink layer sits on the same gray layer, with the same thickness. Term: ______. So the geologist concludes that ______.1 pt
4.In a quarry the layers stand nearly on end, like books on a shelf. Term: ______. So the geologist concludes that ______.1 pt
5.A cliff shows twelve flat layers that have never been bent or broken; the geologist wants the youngest. Term: ______. So the geologist concludes that ______.1 pt
6.In Ohio and in Morocco, the same three shell species appear in the same order from bottom to top, even though the rocks look different. Term: ______. So the geologist concludes that ______.1 pt
7.A lab crushes a piece of volcanic rock, measures its uranium and lead, and reports 1,408 million years. Term: ______. So the geologist concludes that ______.1 pt
Part C: Complete the concept map
8.Write the term for each blank, then write the number of the Part B situation (q2 to q7) that used that same term. One blank has no Part B match; write 'none' for it.5 pts
| Blank | Term | Matching Part B situation |
|---|
| Blank 1 | | |
| Blank 2 | | |
| Blank 3 | | |
| Blank 4 | | |
| Blank 5 | | |
Part D: Tell them apart
9.Relative dating and absolute dating both answer 'how old?' Write one sentence for each that shows how their answers are different in kind.2 pts
10.A certain clam species lived for 300 million years, was found on every continent, and has an easy-to-spot ribbed shell. Explain, using the definition, why it is still a poor index fossil.2 pts
11.An intrusion and a fault are both features that cut across rock. Write one way they are alike in what they tell a geologist, and one way they are different in what they are made of or how they form.2 pts
Part E: The terms on a birthday cake
12.A baker builds a four-layer cake one layer at a time, then pushes a candle down through the top three layers, then cuts out one slice and lifts it away. Write a short paragraph describing the cake using law of superposition, law of cross-cutting relationships and principle of lateral continuity correctly (bold or underline each term). Then write one sentence explaining which real rock feature the candle is most like, and why.4 pts
Term families
If the sorting in Part A is hard, start with the names. Terms that begin with 'law of' or 'principle of' are rules. Terms you could point at in a photograph (a layer, a crack, a body of hardened magma, a fossil) are features. What is left is about methods and the numbers they produce. For Part B, ask yourself: is the clue about stacking, spreading sideways, cutting across, fossils in order, or counting atoms?
Write the rule for a worn-down surface
In many cliffs there is a surface where tilted layers were worn flat before new flat layers were laid on top. No single term in the list names that surface, but the law of cross-cutting relationships covers it. Write, in your own words, a one-sentence rule for a worn-down surface that says what it is younger than and what it is older than. Then explain why such a surface always means that some amount of time is missing from the record.