UNIT 10
In the two pictures above, I and II, [See image: UNIT 10.13] show traces of former life in rocks from the Grand Canyon. Each is "typical";the rocks near sample I contain fossils similar to those shown in sample I, and the rocks near sample II contain fossils similar to those shown in sample II. It is likely that: A) Sample I is from higher in the cliffs of the Grand Canyon, and sample II is from much lower, nearer to the river. B) Sample I is from lower, nearer the river, and sample II is from higher in the cliffs of the Grand Canyon. C) Sample I is from low in the cliffs, near the river, and sample II is also from low in the cliffs, near the river. D) Sample I is from high in the cliffs of the Canyon, and sample II is also from high in the cliffs of the Canyon. E) Sample I shows the President's desk, and sample II is the sole of the Speaker of the House's shoe.
A) Sample I is from higher in the cliffs of the Grand Canyon, and sample II is from much lower, nearer to the river. Feedback: Sample I shows reptile tracks from the fossil sand dunes of the Coconino far up the side of the Canyon, and thus shows the presence of complex creatures. Sample II includes algal-mat deposits (stromatolites) from the Precambrian Chuar Group of the Grand Canyon Supergroup, deep in the Canyon near the river, from a time when biology was not a whole lot more diverse than algal mats.
You start with 200 parent atoms of a particular radioactive type, which decays in a single step to give a stable offspring, and you start with none of those stable offspring. You wait just long enough for two half lives to pass. You should expect to have how many offspring atoms (on average)(remember that the number of parents and the number of offspring add up to 200, so if you have 10 parents, you have 190 offspring because 10 and 190 add up to 200, and if you have 20 parents you have 180 offspring, and so on): A) 200. B) 150. C) 100. D) 50. E) 25.
B) 150. Feedback: After one half-life, you've gone from 200 parents to 100, and 100 offspring have been made. In the second half-life, you go from 100 to 50 parents, and that makes another 50 offspring. Adding the additional 50 to the 100 from the previous half-life gives 150 offspring. (Typical studies of radioactive decay use many more atoms, to avoid statistical fluctuations, but the question says "on average", so we asked you about 200 rather than 200,000,000,000,000 to make the math easier.)
What is accurate about the scientific results learned by counting tree rings and other annual layers? A) No known records have more than 5000 layers. B) Records in tree rings, lakes and ice all reach beyond 12,000 years, and some of them reach beyond 40,000 years. C) No known records have more than 6000 layers. D) The longest record of annual layers goes back 12,429 years, but there is no way to check this because there are no other records that long. E) Records in trees, lakes and ice all go back 12,429 years, but none of them are longer than that, so that must be the age of the Earth.
B) Records in tree rings, lakes and ice all reach beyond 12,000 years, and some of them reach beyond 40,000 years.
What is accurate about the scientific results learned by counting tree rings and other annual layers? A) No known records have more than 5000 layers. B) Records in tree rings, lakes and ice all reach beyond 12,000 years, and some of them reach beyond 40,000 years. C) No known records have more than 6000 layers. D) The longest record of annual layers goes back 12,429 years, but there is no way to check this because there are no other records that long. E) Records in trees, lakes and ice all go back 12,429 years, but none of them are longer than that, so that must be the age of the Earth.
B) Records in tree rings, lakes and ice all reach beyond 12,000 years, and some of them reach beyond 40,000 years. Feedback: There is a continuous record of overlapping tree rings from north Germany with 12,429 years in trees (and that was published a few years ago). The longest lake-sediment record of annual layers is over 40,000 years, and there are over 100,000 years sin the longest ice-core record that preserves annual layers. And, various lake, tree and ice records agree on the history of volcanoes, climate changes, etc.
The picture above [See image: UNIT 10.12] shows a very hard piece of rock about six inches across, in the Grand Canyon. The surface of the rock looks rather different from the surfaces of many other rocks. What made this odd-looking surface? A) A glacier; the high plateaus adjacent to the canyon had ice-age glaciers that helped carve the canyon. B) The river, which blasted the rock with sand- and silt-laden water during floods; this shows that even hard rocks can be eroded by rivers. C) The wind, which has been primarily responsible for carrying away sand bars, and which sand-blasts rocks with the sand. D) A fault, which dropped old rocks so that they were preserved in Death-Valley-type valleys and so were not eroded away. E) The river; because the rocks are still there, this shows that rivers cannot really erode hard rocks and thus that the river could not have carved the canyon.
B) The river, which blasted the rock with sand- and silt-laden water during floods; this shows that even hard rocks can be eroded by rivers. Feedback: The Canyon was carved by the Colorado River. Glaciers have not been there, and while wind and faults can change the appearance of rocks, none makes something like this river-polished rock, as you saw in one of the Grand Canyon V-Trips.
The age of the Earth can be estimated in many ways. Which statement below is most accurate (remember that uniformitarian calculations involve looking at the thickness and type of sedimentary rocks, and similar things, but do NOT include radiometric dating or counting of annual layers)? A) Annual-layer counting shows that the Earth is more than about 100 million years old. B) Annual-layer counting shows that the Earth is more than about 100 thousand years old, uniformitarian calculations show that the Earth is more than about 100 million years old, but we don't know how to estimate how much more than 100 million years the Earth is. C) Annual-layer counting shows that the Earth is more than about 100 thousand years old, uniformitarian calculations show that the Earth is more than about 100 million years old, and radiometric techniques tell us how old the Earth is. D) Annual-layer counting shows that the Earth is 4.6 billion years old. E) Uniformitarian calculations show that the Earth is 4.6 billion years old.
C) Annual-layer counting shows that the Earth is more than about 100 thousand years old, uniformitarian calculations show that the Earth is more than about 100 million years old, and radiometric techniques tell us how old the Earth is.
The above photograph was taken in the Grand Canyon, and shows a cliff that is approximately 30 feet high. What are the rocks in the cliff? A) Precambrian sedimentary rocks, preserved in blocks dropped down by Death-Valley-Type faulting; the folding was caused by the drag along the faults. B) Paleozoic sedimentary rocks that form the main walls of the canyon; the folding was caused by mass-movement processes before the rocks were hardened by hard-water deposits. C) Precambrian metamorphic rocks with some igneous rocks intruded; the folding was caused by mountain-building processes when the rocks were very hot deep in a mountain range. D) Recent lava flows from pull-apart faults near the west end of the canyon; the folding happened as the lava cascaded over the canyon walls and flowed toward the river. E) Cement poured to make the walls of the new gift shop that sits above the canyon, painted to look like something more interesting.
C) Precambrian metamorphic rocks with some igneous rocks intruded; the folding was caused by mountain-building processes when the rocks were very hot deep in a mountain range. Feedback: This is the Vishnu Schist and Zoroaster Granite, rocks from the heart of a mountain range. The river is just barely out of the picture to the bottom.
[See image: UNIT 10.10] Two yellow lines have been drawn on the picture by the instructional team. These lines follow an interesting surface, which separate flat-lying sedimentary rocks, on top, from slanting sedimentary rocks beneath. This surface is: A) A great fault, where push-together action shoved the upper rocks over the lower ones. B) A great fault, where pull-apart Death-Valley-type faulting dropped rocks so that they could be preserved from erosion and seen today. C) A great unconformity, with sedimentary rocks above resting on igneous and metamorphic rocks below. D) A great unconformity, with sedimentary rocks above resting on older sedimentary rocks below. E) A great unconformity, with sedimentary rocks above resting on younger sedimentary rocks below.
D) A great unconformity, with sedimentary rocks above resting on older sedimentary rocks below. Feedback: John Wesley Powell, of the United States Geological Survey, and the leader of the first boat trip through the Grand Canyon, called the feature marked by the yellow lines "The Great Unconformity". It separates horizontal Paleozoic sedimentary rocks, above, from inclined Precambrian sedimentary rocks, below.
You are asked to assign as accurate a numerical age as possible (how many years old) to a sedimentary deposit. You would be wise to use: A) Uniformitarian techniques. B) Counting of annual layers if the deposit is old (more than about 100,000 years), and radiometric techniques if the deposit is young (less than about 100,000 years). C) Either counting of annual layers or radiometric techniques if the deposit is old (more than about 100,000 years), and radiometric techniques if the deposit is young (less than about 100,000 years). D) Either counting of annual layers or radiometric techniques if the deposit is young (less than about 100,000 years), and radiometric techniques if the deposit is old (more than about 100,000 years). E) Uniformitarian techniques if the deposit is old, and counting of annual layers if the deposit is young.
D) Either counting of annual layers or radiometric techniques if the deposit is young (less than about 100,000 years), and radiometric techniques if the deposit is old (more than about 100,000 years). Feedback: If you want an absolute date (number of years) rather than older/younger, you can count layers for young things, or use radiometric techniques for young things or for old ones. Uniformitarian calculations aren't very accurate.
Which is accurate about the history of the Grand Canyon: A) The Kaibab limestone that forms the upper rim of the canyon is the youngest rock layer known from Arizona and surrounding states. B) The rock record of the canyon contains exactly one unconformity. C) The canyon is wider at the top and narrower at the bottom because the river was wider when the region was wetter, and has narrowed as deserts spread recently. D) In the deepest part of the canyon, the river cuts through rocks formed by metamorphism of older sedimentary rocks in the heart of a mountain range. E) The oldest rocks are on top, with younger ones beneath, as shown by all of the footprints being upside-down in the rocks of the canyon walls.
D) In the deepest part of the canyon, the river cuts through rocks formed by metamorphism of older sedimentary rocks in the heart of a mountain range. Feedback: The Colorado River is cutting through the metamorphic rocks from the heart of an old mountain range. The sedimentary rocks above are right-side up, and the Kaibab Limestone slants down to the north beneath the rocks of Zion, which are older than the rocks of Bryce, among others. Many unconformities exist in the walls of the Canyon, including the one below the Precambrian sediments and the one above those sediments. The idea of the river narrowing over time was the hypothesis that an interested tourist presented to one of the professors and a ranger at the Canyon a few years ago. When the professor asked whether the tourist would want to go out on a narrow point with a jackhammer, the tourist said no, because the rocks might fall off and slide down into the Canyon. When the professor pointed out the many places that rocks had fallen off and slid down, the quick-witted tourist figured out that the Canyon has been widened by such rockfalls as the river has cut downward.
Geological evidence based on several radiometric techniques has provided a scientifically well-accepted age for the Earth. Represent that age of the Earth as the 100-yard length of a football field, and any time interval can be represented as some distance on the field. (So something that lasted one-tenth of the age of the Earth would be ten yards, and something that lasted one-half of the age of the Earth would be fifty yards.) On this scale, how far on the football field would represent the time between the first appearance of abundant shelly creatures and today? A) Over 80 yards. B) 60 yards. C) 50 yards. D) Just over 10 yards. E) Over 90 yards.
D) Just over 10 yards. Feedback: If the 4.6 billion years of Earth history are 100 yards, then the 570 million years since the widespread appearance of shelly creatures is a bit over 10 yards. Most of our fossil record is limited to the last 10% of the planet's history. The shells appeared "suddenly"—in a few million years, or a few inches on the football field of time.
You are dating a lava flow by the potassium-argon system. However, the offspring in this system are leaking out of the minerals. Which is accurate? A) You will think that the lava flow is older than it really is, and you will have no way to detect your error. B) You will think that the lava flow is younger than it really is, and you will have no way to detect your error. C) You will think that the lava flow is older than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains. D) You will think that the lava flow is younger than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains. E) You will get the age exactly right without worrying about any complications.
D) You will think that the lava flow is younger than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains. Feedback: Argon-40 leakage will make the lava flow appear young even if the flow is old; however, the edges of grains will lose more argon-40 than will the centers, pointing to the source of the error.
