Challenge and Extension

LS Chapter 5 C&E

5.1

CHALLENGE AND EXTENSION

1. rubidium-87, carbon-14

2. uranium-238

3. If half the uranium-235 was left, that means that half of it had decayed. According to the chart, the half-life of uranium-235 is 0.7 billion years. So, the sample is about 0.7 billion years old.

4. Sample answer: Certain rocks may not contain certain radioactive elements. The elements with longer half-lives would be more useful for dating older rocks, while the elements with shorter half-lives would be more useful for dating younger rocks.

5.2

CHALLENGE AND EXTENSION

1. the Proterozoic; the Hadean

2. The other three eons were before the Phanerozoic eon. Looking at the pie graph, these three eons together make up between 80 and 90 percent of Earth’s history. The total of those three eons is 4056 million years, while all four eons total up to 4600 million years. The first three eons, therefore, come out to about 88 percent of Earth’s history.

3. Because the Phanerozoic eon is closer to our own time, scientists are better able to use fossil records to find out about it.

4. 65 million years; 0.014 percent

5.3

CHALLENGE AND EXTENSION

1. The oldest ice is at the top, because the cup was turned upside down to get the ice out, and the oldest ice was the ice formed at the bottom.

2. You could break the ice into pieces and then melt the pieces to find out what is in each layer. You could dry the materials, and then use observations such as sight and smell to distinguish the materials.

3. The ingredients might represent dust, pollen, spores, seeds, microscopic organisms, and more.

Optional

Results should be similar to those described in the introduction. Students should conclude that ice cores can be helpful to scientists in understanding the environment at a particular period in Earth’s past. The ingredients represent the environment and what might have been happening on Earth’s surface and in the atmosphere.