Fossils can be used to match up rock layers. As organisms change over time, they look different. Older fossils will look different than younger fossils. Some organisms only survived for a short time before going extinct. Knowing what organisms looked like at certain times also helps date rock layers. Some fossils are better than others for this use. The fossils that are very distinct at certain times of Earths history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure 2.30. If two rock layers have the same index fossils, then they're probably about the same age.

Question: "How are fossils used to match up rock layers?"

Answer: "They leave behind sediment"

Response: no

At 8:38, Ong told Gonzalez that the plane was flying erratically again. Around this time Sweeney told Woodward that the hijackers were Middle Easterners, naming three of their seat numbers. One spoke very little English and one spoke excellent English. The hijackers had gained entry to the cockpit, and she did not know how. The aircraft was in a rapid descent. At 8:41, Sweeney told Woodward that passengers in coach were under the impression that there was a routine medical emergency in first class. Other flight attendants were busy at duties such as getting medical supplies while Ong and Sweeney were reporting the events. At 8:41, in American's operations center, a colleague told Marquis that the air traffic controllers declared Flight 11 a hijacking and "think he's [American 11] headed toward Kennedy [airport in New York City]. They're moving everybody out of the way. They seem to have him on a primary radar. They seem to think that he is descending." At 8:44, Gonzalez reported losing phone contact with Ong. About this same time Sweeney reported to Woodward, "Something is wrong. We are in a rapid descent . we are all over the place." Woodward asked Sweeney to look out the window to see if she could determine where they were.

Question: "What did Sweeney tell Woodward s/he was alarmed about around 8:44?"

Answer: "Something is wrong, We are in a rapid descent . we are all over the place.""

Response: yes

The inhabited history of the Las Vegas Valley stretches to 23,000 b.c. , when much of the area was covered by a prehistoric lake. During this period, the indigenous people lived in caves, hunting the mammals that gathered at the shoreline. The landscape of the valley changed dramatically over the next 200 centuries. The glaciers feeding the lake melted away and the lake evaporated. Fossils tell an obscure story of man's slow and sporadic development. Around 3000 b.c. , native Archaic Indians began to develop a lasting hunting and gathering culture. By this time, the valley was in much the same geographic state as it exists in today, with one exceptionthe presence of artesian springs that bubbled to the surface in several areas. These springs fed a network of streams draining through the Las Vegas Wash to the Colorado River. The areas surrounding the springs were desert oases: sprawling collections of grasses, trees, and wildlife. Many springs lay in areas that would eventually become the center of the modern Las Vegas metropolis. For about 4000 years, the Archaics thrived in a culture that included many signs of early civilization. Signs of even more advancement appeared halfway through the first millennium a.d. , when the Anasazi Indians inhabited the valley. Far more progressive than the Archaics, the Anasazi utilized such formal agricultural techniques as irrigation to assist their harvest. This permitted the Anasazi to achieve a benchmark of advanced societythe ability to live in permanent shelters year-round without need to follow wildlife. Mysteriously, the Anasazi vanished from the valley around a.d.

Question: "Why did the prehistoric lake disappear from the Las Vegas Valley?"

Answer: "The region was over populated"

Response: no

Greta ran to the corner with her older brother Tony. He had money for the ice cream truck in his pocket and she was very happy. The ice cream truck had been parked at the curb waiting for children for a very long time. The ice cream truck driver thought that no more children were coming to get ice cream so he started pulling away from the curb when they got to the corner. They yelled. They screamed, "Stop! Stop!" and jumped up and down on the side walk trying to get him to see them. The driver of the truck saw them, waved at them and smiled, pulled back to the curb and opened his truck up so that they could see everything that he had for sale. They were so excited. They saw some new treats. Tony wanted to try something new. He got an ice cream sundae with chocolate ice cream and nuts. He almost got a snow cone. Greta looked at everything that the ice cream truck had. She saw candy, ice cream cones, snow cones, and everything else. It all looked so good. But after looking at everything, she wanted to get an ice cream sandwich. She got the ice cream sandwich. She bit into it and smiled. It tasted so good. She felt so happy. Her brother, Tony, was happy too. He bit into his ice cream cone sundae and grinned. They walked home with their ice cream and told their mom about how close they came to not getting their ice cream at all. Their mom was happy that the truck had stopped for them. She said that they were very lucky to have gotten to the curb before the ice cream truck left.

Question: "How many times did they have to tell the ice cream truck driver to stop?"

Answer: "Three times"

Response:
no