Rock On 10

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):

50.

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:

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).

Which is accurate about the history of the Grand Canyon:

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.

Early geologists did not have radiometric dating techniques, or long layer-counted histories. Instead, they followed William Smith in putting things in order, and then used uniformitarian calculations based on modern rates of processes and observed results of processes in the geologic record. These early geologists, using these techniques, found that the Earth:

Is more than about one-hundred-million years old.

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.

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?

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.

The two pictures above, I and II, show fossils inrocks from the Grand Canyon. Each is "typical"; the rocks near sample Icontain fossils similar to those shown in sample I, and the rocks nearsample 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.

In the two pictures above, I and II, 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:

Sample I is from higher in the cliffs of the Grand Canyon, and sample II is from much lower, nearer to the river.

Which is not accurate about the Grand Canyon, in Arizona:

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.

One practical radioactive system used to date lava flows involves:

The solid potassium-40, which decays to the gas argon-40.

John Wesley Powell, who led the first boat trip through the Grand Canyon, called the feature marked by the yellow lines "The Great _________". What did he put in the blank?

Unconformity.

The picture above shows a region of hard rock about six inchesacross from the Grand Canyon. The shape and polish of the rock areinteresting. It is likely that the rock:

Was scratched and polished by silt-laden river water, during carving of the Canyon by the Colorado River.

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?

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.

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 long have you personally been alive?

Much less than the thickness of a sheet of paper.

What is accurate about the scientific results learned by counting tree rings?

Study of tree rings and associated geology shows that the Earth is more than 12,429 years old.