Overview

Lesson Procedure

65-75 minutes of class time across 5 phases.

1. Warm-Up10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice15-20 minutes
5. Closure5-10 minutes

1. Warm-Up10 minutes

   Hold up a piece of natural chalk, or a calcium carbonate antacid tablet if you have no natural chalk. Many modern classroom chalks are made of gypsum (calcium sulfate) instead, which is why the optional vinegar test below needs natural chalk or the tablet. Ask the question on the board.

   Warm-Up Prompt

   "Where did this piece of chalk come from, before it was a stick in a box? Write the steps you think it went through, in order. Then write one sentence that says what your steps add up to."

   Collect two or three answers. Point out that most answers are a list of steps, and that the last sentence is different in kind: it says what the steps mean. Name the two: the steps are a process, and the sentence that says what they add up to is a central idea or conclusion. Tell students that RST.9-10.2 asks for both, plus an accurate summary, and that a scientist asked exactly this question about chalk in 1868. Optional: with goggles on, drop the chalk or tablet into the vinegar and let students watch the bubbles; Huxley describes the same test in the first passage.

2. Direct Instruction20 minutes

   Part 1: Four terms. Put the table on the board and keep it up for the whole lesson.

   Four terms for reading a science text

   Term	What it is	Test
   Topic	What the text is about, in a word or phrase	It is not a sentence: "chalk"
   Central idea or conclusion	What the text claims or shows about the topic	A full sentence someone could disagree with or test
   Process or line of reasoning	The steps, in order, that the text explains, with what links them (because, then, so)	Could you put the steps on numbered cards and order them?
   Accurate summary	The central idea and the key steps, in order and in your own words	Nothing changed, nothing added, nothing important dropped

   Part 2: Model with Huxley. Explain the setting: Huxley spoke to working men in Norwich, a city built on chalk, and he asks two questions just before this passage: "What is this wide-spread component of the surface of the earth? and whence did it come?" ("whence" means from where). Read the first passage aloud. Then work through the examples, asking after each: is this a topic, a step or a conclusion? Diagram 1 shows where this passage sits in Huxley's whole argument.

   1We all know that if we "burn" chalk the result is quicklime. Chalk, in fact, is a compound of carbonic acid gas and lime, and when you make it very hot the carbonic acid flies away and the lime is left.

   2By this method of procedure we see the lime, but we do not see the carbonic acid. If, on the other hand, you were to powder a little chalk, and drop it into a good deal of strong vinegar, there would be a great bubbling and fizzing, and, finally, a clear liquid, in which no sign of chalk would appear. Here you see the carbonic acid in the bubbles; the lime, dissolved in the vinegar, vanishes from sight. There are a great many other ways of showing that chalk is essentially nothing but carbonic acid and quicklime. Chemists enunciate the result of all the experiments which prove this, by stating that chalk is almost wholly composed of "carbonate of lime."

   3It is desirable for us to start from the knowledge of this fact, though it may not seem to help us very far towards what we seek. For carbonate of lime is a widely-spread substance, and is met with under very various conditions. All sorts of limestones are composed of more or less pure carbonate of lime. The crust which is often deposited by waters which have drained through limestone rocks, in the form of what are called stalagmites and stalactites, is carbonate of lime. Or, to take a more familiar example, the fur on the inside of a tea-kettle is carbonate of lime; and, for anything chemistry tells us to the contrary, the chalk might be a kind of gigantic fur upon the bottom of the earth-kettle, which is kept pretty hot below.

   • Topic versus conclusion

     Is "chalk is made of carbonate of lime" the central idea of this passage?

     Result: It is only the first step. The conclusion of the passage comes in paragraph 3: the chemical fact "may not seem to help us very far towards what we seek," because carbonate of lime "is met with under very various conditions." A one-sentence conclusion: chemistry shows that chalk is almost wholly carbonate of lime, but because that substance forms in many different ways, chemistry alone cannot tell us where chalk came from.

   • Tracing a process: two tests

     How do the two tests in paragraphs 1-2 together show what chalk is made of?

     Result: Test 1: heat the chalk strongly, "the carbonic acid flies away and the lime is left"; students see the lime but not the gas. Test 2: drop powdered chalk into strong vinegar; "you see the carbonic acid in the bubbles" while "the lime, dissolved in the vinegar, vanishes from sight." Each test shows one part, so together they show both. In modern terms, calcium carbonate breaks down into calcium oxide and carbon dioxide.

   • Accurate or not?

     A student summarizes paragraph 3 as "Huxley says chalk is a giant kettle fur on the bottom of the earth." Is it accurate?

     Result: No. Huxley says only that "for anything chemistry tells us to the contrary, the chalk might be a kind of gigantic fur" (emphasis added). He is showing what chemistry cannot rule out, not stating what chalk is. An accurate version: chemistry alone cannot rule out that chalk formed the way kettle fur does, so another test is needed.

   • What a summary leaves out

     Paragraph 3 names limestones, stalagmites, stalactites and kettle fur. Does a summary need all four?

     Result: No. All four are examples of one point: carbonate of lime "is a widely-spread substance." A summary states the point and may name one example; it keeps the reason the point matters (the origin of chalk is still open). Summary of T1 in two sentences: Heating chalk and dissolving it in vinegar show that it is almost wholly carbonate of lime. Since that substance forms in many ways, from limestone to the crust inside a kettle, chemistry cannot yet say where chalk came from.

3. Guided Practice15 minutes

   Pairs read the next passage, in which Huxley tries "another method." They fill in a four-column chart: step, what Huxley does, what he finds, why it matters to the question. Circulate and push for links: "he uses a microscope" is a step; "a slice of kettle fur shows only 'a more or less distinctly laminated mineral substance, and nothing more,' so the chambered bodies in chalk must mean something" traces the reasoning.

   1Let us try another method of making the chalk tell us its own history. To the unassisted eye chalk looks simply like a very loose and open kind of stone. But it is possible to grind a slice of chalk down so thin that you can see through it--until it is thin enough, in fact, to be examined with any magnifying power that may be thought desirable. A thin slice of the fur of a kettle might be made in the same way. If it were examined microscopically, it would show itself to be a more or less distinctly laminated mineral substance, and nothing more.

   2But the slice of chalk presents a totally different appearance when placed under the microscope. The general mass of it is made up of very minute granules; but imbedded in this matrix, are innumerable bodies, some smaller and some larger, but, on a rough average, not more than a hundredth of an inch in diameter, having a well-defined shape and structure. A cubic inch of some specimens of chalk may contain hundreds of thousands of these bodies, compacted together with incalculable millions of the granules.

   3The examination of a transparent slice gives a good notion of the manner in which the components of the chalk are arranged, and of their relative proportions. But, by rubbing up some chalk with a brush in water and then pouring off the milky fluid, so as to obtain sediments of different degrees of fineness, the granules and the minute rounded bodies may be pretty well separated from one another, and submitted to microscopic examination, either as opaque or as transparent objects. By combining the views obtained in these various methods, each of the rounded bodies may be proved to be a beautifully-constructed calcareous fabric, made up of a number of chambers, communicating freely with one another. The chambered bodies are of various forms. One of the commonest is something like a badly-grown raspberry, being formed of a number of nearly globular chambers of different sizes congregated together. It is called Globigerina, and some specimens of chalk consist of little else than Globigerinae and granules.

   4Let us fix our attention upon the Globigerina. It is the spoor of the game we are tracking. If we can learn what it is and what are the conditions of its existence, we shall see our way to the origin and past history of the chalk.

   Each pair then writes a two- or three-sentence summary of the passage and compares it with Diagram 2. Debrief with one question: Why does Huxley stop at paragraph 4 instead of saying where chalk came from? Students should see that the passage ends with a plan, not a conclusion: "If we can learn what it is and what are the conditions of its existence, we shall see our way to the origin and past history of the chalk." A summary that claims Huxley has already proved the origin is not accurate.

   For Activity 2 (Summary Repair Shop). The passage below comes later in the lecture, after Huxley describes how ships sounding the Atlantic for the telegraph cable brought up mud from depths of 10,000 to 15,000 feet. The "[...]" marks five paragraphs left out, in which he discusses whether the Globigerinae live on the sea floor. The practice summary after it was written for this page.

   1Almost the whole of the bottom of this central plain (which extends for many hundred miles in a north and south direction) is covered by a fine mud, which, when brought to the surface, dries into a greyish-white friable substance. You can write with this on a blackboard, if you are so inclined; and, to the eye, it is quite like very soft, greyish chalk. Examined chemically, it proves to be composed almost wholly of carbonate of lime; and if you make a section of it, in the same way as that of the piece of chalk was made, and view it with the microscope, it presents innumerable Globigerinae, embedded in a granular matrix.

   2Thus this deep-sea mud is substantially chalk. I say substantially, because there are a good many minor differences: but as these have no bearing on the question immediately before us,--which is the nature of the Globigerinae of the chalk,--it is unnecessary to speak of them.

   3Globigerinae of every size, from the smallest to the largest, are associated together in the Atlantic mud, and the chambers of many are filled by a soft animal matter. This soft substance is, in fact, the remains of the creature to which the Globigerina shell, or rather skeleton, owes its existence--and which is an animal of the simplest imaginable description. It is, in fact, a mere particle of living jelly, without defined parts of any kind--without a mouth, nerves, muscles, or distinct organs, and only manifesting its vitality to ordinary observation by thrusting out and retracting from all parts of its surface, long filamentous processes, which serve for arms and legs. Yet this amorphous particle, devoid of everything which, in the higher animals, we call organs, is capable of feeding, growing, and multiplying; of separating from the ocean the small proportion of carbonate of lime which is dissolved in sea-water; and of building up that substance into a skeleton for itself, according to a pattern which can be imitated by no other known agency.

   [...]

   4However, the important points for us are, that the living Globigerinae are exclusively marine animals, the skeletons of which abound at the bottom of deep seas; and that there is not a shadow of reason for believing that the habits of the Globigerinae of the chalk differed from those of the existing species. But if this be true, there is no escaping the conclusion that the chalk itself is the dried mud of an ancient deep sea.

   In this passage Huxley describes the mud that covers the shallow sea floor near the coasts of Ireland and Newfoundland. The mud is so much like chalk that you can write on a blackboard with it, and this is Huxley's most important point. Under the microscope the mud is full of Globigerinae, the skeletons of complex little animals with mouths and simple nerves. These creatures build their skeletons from the carbonate of lime that is dissolved in sea-water. Huxley's discovery was the greatest of the nineteenth century, and it proves that the white cliffs of Dover were once at the bottom of the Atlantic Ocean.

4. Independent Practice15-20 minutes

   Students read the passage below and answer quiz questions 1-20 on their own with the passage open. Paragraph numbers are printed beside the text. Glosses: a valve is one half of a two-part shell; a Micraster is one kind of fossil sea-urchin; a coralline is a small sea animal that grows in colonies; putrefaction means rotting. Huxley's footnote marks are left out.

   1There is more curious evidence, again, that the process of covering up, or, in other words, the deposit of Globigerinae skeletons, did not go on very fast. It is demonstrable that an animal of the cretaceous sea might die, that its skeleton might lie uncovered upon the sea-bottom long enough to lose all its outward coverings and appendages by putrefaction; and that, after this had happened, another animal might attach itself to the dead and naked skeleton, might grow to maturity, and might itself die before the calcareous mud had buried the whole.

   2Cases of this kind are admirably described by Sir Charles Lyell. He speaks of the frequency with which geologists find in the chalk a fossilized sea-urchin, to which is attached the lower valve of a Crania. This is a kind of shell-fish, with a shell composed of two pieces, of which, as in the oyster, one is fixed and the other free.

   3"The upper valve is almost invariably wanting, though occasionally found in a perfect state of preservation in the white chalk at some distance. In this case, we see clearly that the sea-urchin first lived from youth to age, then died and lost its spines, which were carried away. Then the young Crania adhered to the bared shell, grew and perished in its turn; after which, the upper valve was separated from the lower, before the Echinus became enveloped in chalky mud."

   4A specimen in the Museum of Practical Geology, in London, still further prolongs the period which must have elapsed between the death of the sea-urchin, and its burial by the Globigerinae. For the outward face of the valve of a Crania, which is attached to a sea-urchin (Micraster), is itself overrun by an incrusting coralline, which spreads thence over more or less of the surface of the sea-urchin. It follows that, after the upper valve of the Crania fell off, the surface of the attached valve must have remained exposed long enough to allow of the growth of the whole coralline, since corallines do not live imbedded in mud.

   5The progress of knowledge may, one day, enable us to deduce from such facts as these the maximum rate at which the chalk can have accumulated, and thus to arrive at the minimum duration of the chalk period. Suppose that the valve of the Crania upon which a coralline has fixed itself in the way just described, is so attached to the sea-urchin that no part of it is more than an inch above the face upon which the sea-urchin rests. Then, as the coralline could not have fixed itself, if the Crania had been covered up with chalk mud, and could not have lived had itself been so covered, it follows, that an inch of chalk mud could not have accumulated within the time between the death and decay of the soft parts of the sea-urchin and the growth of the coralline to the full size which it has attained. If the decay of the soft parts of the sea-urchin; the attachment, growth to maturity, and decay of the Crania; and the subsequent attachment and growth of the coralline, took a year (which is a low estimate enough), the accumulation of the inch of chalk must have taken more than a year: and the deposit of a thousand feet of chalk must, consequently, have taken more than twelve thousand years.

5. Closure5-10 minutes

   Exit ticket: "In one sentence, state the conclusion Huxley reaches across the three passages you read in class (T1, T2 and T3). Then list the three tests that led him there, in order." Sort the tickets into "topic only," "steps without a conclusion" and "conclusion with steps" to plan the next lesson.

   Teacher note on the 1868 science. Huxley's reasoning holds up, but several of his facts have changed. Discuss these after the quiz and homework, and keep them separate from what the text says. (1) Terms: his "carbonate of lime" is calcium carbonate, "lime" or "quicklime" is calcium oxide, and "carbonic acid" gas is carbon dioxide. (2) Globigerina is not an animal: it is a foraminiferan, a single-celled organism. Its kind lives in the upper waters of the open ocean, and the shells sink to the floor after death; in the paragraphs left out of T3, Huxley argued that they lived on the sea floor, which later ocean surveys disproved. (3) Most of the fine "granules" in chalk are coccoliths, tiny plates made by single-celled algae; later in this lecture Huxley describes naming them and says he doubted they were even organic. (4) The chalk sea was a shelf sea, far shallower than the Atlantic plain: most estimates put it at roughly 50 to 300 meters deep. (5) Geologists now date the English chalk to roughly 100 to 66 million years ago, using methods that did not exist in 1868. Compare this with Huxley's own estimate only after students have worked it out in the quiz.

   Teacher note on the language. The passages keep Huxley's spelling and words exactly ("imbedded," "greyish," "bolls" for tree trunks, "stools" for stumps, "whoso runs may read it" for "anyone can read it"). He calls Globigerina "an animal of the simplest imaginable description," which was the classification of his time. The homework passage also has one dated idea: see the note below.

   Homework passage. The homework uses the passage below, from near the end of the lecture, in which Huxley reads the history of the cliffs at Cromer on the Norfolk coast. Boulder clay (also called drift) is a mix of clay and stones, some carried from as far as Norway. Huxley's account of how it was laid down reflects the geology of the 1860s; geologists now explain most of it as material left by ice sheets during the ice ages. Tell students to summarize what Huxley says, and to keep modern corrections for a separate sentence if they add one.

   1The chalk, then, is certainly older than the boulder clay. If you ask how much, I will again take you no further than the same spot upon your own coasts for evidence. I have spoken of the boulder clay and drift as resting upon the chalk. That is not strictly true. Interposed between the chalk and the drift is a comparatively insignificant layer, containing vegetable matter. But that layer tells a wonderful history. It is full of stumps of trees standing as they grew. Fir-trees are there with their cones, and hazel-bushes with their nuts; there stand the stools of oak and yew trees, beeches and alders. Hence this stratum is appropriately called the "forest-bed."

   2It is obvious that the chalk must have been upheaved and converted into dry land, before the timber trees could grow upon it. As the bolls of some of these trees are from two to three feet in diameter, it is no less clear that the dry land thus formed remained in the same condition for long ages. And not only do the remains of stately oaks and well-grown firs testify to the duration of this condition of things, but additional evidence to the same effect is afforded by the abundant remains of elephants, rhinoceroses, hippopotamuses, and other great wild beasts, which it has yielded to the zealous search of such men as the Rev. Mr. Gunn.

   3When you look at such a collection as he has formed, and bethink you that these elephantine bones did veritably carry their owners about, and these great grinders crunch, in the dark woods of which the forest-bed is now the only trace, it is impossible not to feel that they are as good evidence of the lapse of time as the annual rings of the tree-stumps.

   4Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs may read it. It tells us, with an authority which cannot be impeached, that the ancient sea-bed of the chalk sea was raised up, and remained dry land, until it was covered with forest, stocked with the great game whose spoils have rejoiced your geologists. How long it remained in that condition cannot be said; but "the whirligig of time brought its revenges" in those days as in these. That dry land, with the bones and teeth of generations of long-lived elephants, hidden away among the gnarled roots and dry leaves of its ancient trees, sank gradually to the bottom of the icy sea, which covered it with huge masses of drift and boulder clay. Sea-beasts, such as the walrus, now restricted to the extreme north, paddled about where birds had twittered among the topmost twigs of the fir-trees. How long this state of things endured we know not, but at length it came to an end. The upheaved glacial mud hardened into the soil of modern Norfolk. Forests grew once more, the wolf and the beaver replaced the reindeer and the elephant; and at length what we call the history of England dawned.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   In paragraph 1, what does Huxley mean by "the process of covering up"?

   AThe rotting of dead animals on the sea floor BThe growth of shells over other shells CThe laying down of Globigerinae skeletons DThe way geologists cover fossils to protect them

2. Question 2 of 20 · Multiple Choice

   According to paragraph 2, what is a Crania?

   AA kind of sea-urchin whose long spines are carried away when it dies BA shell-fish with a two-piece shell, one piece fixed and one free CA coral that grows over other animals DThe chalky mud that buries the fossils

3. Question 3 of 20 · Multiple Choice

   Which part of the Crania do geologists usually find still attached to the fossil sea-urchin?

   AThe lower valve BThe upper valve CBoth valves, closed together DOnly the soft parts, turned to chalk

4. Question 4 of 20 · Multiple Choice

   According to Lyell's account in paragraph 3, when did the sea-urchin lose its spines?

   AWhile it was still alive and young BAfter the Crania had grown to full size on it CAfter the chalky mud had covered it DAfter it died, and before the young Crania attached to it

5. Question 5 of 20 · Multiple Choice

   In paragraph 3, what does "the Echinus" refer to?

   AThe Crania BThe sea-urchin CThe coralline DThe upper valve

6. Question 6 of 20 · Multiple Choice

   What does the specimen in the Museum of Practical Geology add to Lyell's case?

   AThe upper valve of the Crania never formed, so nothing fell off BThe sea-urchin was buried before the Crania on it had died CA coralline grew on the bare Crania valve, so burial came later still DCorallines can go on living and growing after chalky mud buries them

7. Question 7 of 20 · Multiple Choice

   Why does the coralline prove that the Crania valve stayed uncovered?

   ABecause corallines do not live buried in mud BBecause the coralline was larger than the sea-urchin CBecause the coralline ate the chalky mud DBecause corallines grow only on living animals

8. Question 8 of 20 · Multiple Choice

   In paragraph 5, Huxley links "the maximum rate at which the chalk can have accumulated" with "the minimum duration of the chalk period." Why do the two go together?

   AA faster rate of building up means the chalk period lasted longer BThe rate and the duration cannot be connected to each other CThe minimum duration is the time it took for one inch of chalk DThe fastest possible rate gives the shortest possible time

9. Question 9 of 20 · Multiple Choice

   In Huxley's calculation, what does the one inch measure?

   AThe thickness of the lower valve of the Crania BHow high the Crania valve rises above where the sea-urchin rests CThe length of a sea-urchin spine DThe thickness of chalk laid down in one year, which Huxley measured directly

10. Question 10 of 20 · Multiple Choice

    Huxley assumes that less than an inch of chalk mud built up in a year. Which calculation gives his minimum for a thousand feet of chalk?

    A1,000 × 1 = 1,000 years B1,000 × 12 = 12,000 years C1,000 ÷ 12 ≈ 83 years D1,000 × 365 = 365,000 years

11. Question 11 of 20 · Multiple Choice

    Using the same reasoning, what is the minimum time for a chalk cliff 300 feet thick?

    AMore than 43,200 years BMore than 25 years CMore than 3,600 years DMore than 300 years

12. Question 12 of 20 · Multiple Choice

    Huxley writes that a year is "a low estimate enough." What does this phrase tell the reader about his result?

    AThe events likely took longer, so the chalk took even longer too BHe thinks a year is too long, so his figure is too high CHe is sure the events took exactly one year, no more DHe thinks the calculation is useless and should be ignored

13. Question 13 of 20 · Multiple Choice

    Which detail could an accurate summary of the passage leave out without losing a step of the argument?

    AThat the upper valve fell off before the burial BThat corallines do not live in mud CThat the thousand feet took more than twelve thousand years DThat the specimen is in a museum in London

14. Question 14 of 20 · Multiple Choice

    Which is an accurate paraphrase of Lyell's sentence "after which, the upper valve was separated from the lower, before the Echinus became enveloped in chalky mud"?

    AThe mud covered the sea-urchin, and then the top shell of the Crania fell away BThe top shell of the Crania was never attached to the lower one CThe Crania's loose top shell fell away before mud covered the sea-urchin DThe sea-urchin pushed the top shell off the Crania

15. Question 15 of 20 · Short Answer

    Trace the full sequence of events from the sea-urchin's life to its burial, using paragraphs 3 and 4. Give at least six steps in order, and quote the word or phrase that signals the order for at least two of them.

    Show model answer

16. Question 16 of 20 · Short Answer

    State the central conclusion of the passage in your own words, in one sentence. Then quote the words in paragraph 5 that state its result.

    Show model answer

17. Question 17 of 20 · Short Answer

    Paragraph 1 makes a general claim, and paragraphs 2-4 give a specific case. Explain how the case supports the claim. Quote one phrase from paragraph 1 and one from paragraph 3 or 4.

    Show model answer

18. Question 18 of 20 · Short Answer

    Huxley's figure depends on one assumption. Name it, and use his method to find the minimum time for the thousand feet of chalk if those events took ten years instead of one. Show the arithmetic.

    Show model answer

19. Question 19 of 20 · Short Answer

    Write an accurate summary of the passage in three or four sentences for a classmate who has not read it. Keep the steps in order and add nothing from outside the passage.

    Show model answer

20. Question 20 of 20 · Short Answer

    A classmate writes: "Huxley shows that dead sea-urchins were buried by chalk mud almost as soon as they died, and he calculates that the thousand feet of chalk took exactly twelve thousand years to form." Correct both errors with quotations from the passage.

    Show model answer

These standards connect to RST.9-10.2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.