GeoSci 10 - 2019: RockOn#10

What is indicated by the yellow lines in the image above, which separate flat-lying sedimentary rocks, on top, from slanting sedimentary rocks beneath?

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 start with 400 parent atoms of a particular radioactive type, which decays to give stable offspring. You wait just long enough for three half lives to pass. You should expect to have how many parent atoms remaining (on average):

A) 50 Feedback: After one half-life, you've gone from 400 parents to 200; after a second half-life you go from 200 parents to 100, and after a third half-life you go from 100 parents to 50. (Typical studies of radioactive decay use many more atoms, to avoid statistical fluctuations, but the question says "on average", so we asked you about 400 rather than 400,000,000,000,000 to make the math easier.)

Which is the correct age progression, from younger (first) to older (last)? A) D, E, F, B, C B) C, D, E, F, B C) E, F, B, C, D D) B, F, E, D, C E) B, C, D, E, F

D) B, F, E, D, C

Which correctly gives the order of the faults, from youngest (first) to oldest (last): A) I, J, H B) I, H, J C) H, I, J D) H, J, I E) J, H, I

D) H, J, I

Which is younger:

Fault I. Feedback: Unconformity L is cut by fault I, so is older than I. Fault I is cut by fault J, so is older than J. Fault J is cut by unconformity K so is older than K. Unconformity K is cut by intrusion G so is older than G, and intrusion G is cut by fault H so is older than H. Hence, fault H is the youngest.

Which is accurate about the history of the Grand Canyon:

In the deepest part of the canyon, the river cuts through rocks form by metamorphism of older sedimentary rocks in the heart of the mountain range

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, the time from when dinosaur extinction made space for large mammals, until today, would be represented by how far on the football field?

Just over 10 yards

From what location in the Grand Canyon did Dr. Alley take this image?

Near the bottom, where the river has cut through rock that were cooked, squeezed, and partially melted deep in an old mountain range

In age dating, geologists use:

Radiometric techniques and layer-counting for absolute dating of events that happened in the last 100,000 years, and other radiometric techniques for absolute dating of much older events

What is accurate about the scientific results learned by counting tree rings and other annual layers?

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 in 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 two pictures above, I and II, show fossils 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:

Sample I is from high in the cliffs of the Grand Canyon, and sample II is from much lower, near the river. Feedback: Sample I is a wonderful shell hash, or coquina, from the Supai Rocks well up the side of the Canyon, and contains shells from a great diversity of different 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. Lake Winna-Bango featured in the gripping Dr. Suess tale of Thidwick, the Big-Hearted Moose, but is not pictured here.

One practical radioactive system used to date lava flows involves:

The solid potassium-40, which decays to the gas argon-40. Feedback: Potassium-40 is common in solid minerals, and decays to produce the gas argon-40. And despite his great contributions to humanity, no one has named an isotope after moose moss (the favorite food of Thidwick, for you Dr. Suess fans).

The picture above 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?

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

Which is younger:

The tree. Feeback: The tree is growing on intrusion G, which can be shown to be younger than all of the others.

What do uniformitarian calculations show (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)?

Uniformitarian calculations show that the Earth is more than about 100 million years old, and radiometric techniques tell us how much older