As demonstrated by the work of archaeologists at the Mesa site, scientists play a critical role in helping us learn about our past. As the world population grows and the Earth becomes increasingly affected by our activities, an understanding of past human activity and its effect on the natural environment can help us address the problems of the modern world. For example, one way archaeologists and historians can help today's land managers is to examine floral or faunal evidence at archaeological sites to identify plants and animals that have disappeared from an area and analyze the probable causes for their disappearance. Several of the interdisciplinary classroom activities that follow focus on this theme and introduce science learning in the broader context of learning about the past.

The Line On Time
Refer to the posterback links as you lead your class in a discussion about the emergence and distribution of people in North America. Ask students, When do you think this took place? Let them create an illustrated time line depicting various periods from earliest geologic time to the present. Explain that currently scientists believe that humans, as a species, were not present until the Pliocene epoch, 3.5 million years ago. Because of the long period of geologic time and comparatively short period that humans have been on Earth you will need two charts. Begin with the geologic chart. Guide students in calculating how long a piece of paper is needed to chart 600 million years if each year equals one millimeter. The answer is 600 kilometers - that certainly won't fit in the classroom! Ask students for other suggestions. For a more reasonable result, let each 100 million years equal one meter. Place the chart on the classroom wall and let your class illustrate it. Geologic time will probably be new to students, so describe each period, beginning with the Cambrian, and discuss the commonly associated animals and plants. For example, the Cambrian period is known for trilobites, the Devonian for fishes, and the Jurassic for dinosaurs. As an alternative, have students make a pie chart of geologic time with each era represented as a percentage of the whole.

Comparing a time line of the human species with a geologic time line will help children gain perspective on the place of humans in the history of the Earth.

Exploring Extinction
Woolly mammoths, giant bison, huge beavers, giant sloths, and large armadillos were a few of the great mammals once hunted by America's first settlers but now extinct. Lead students in a discussion of the reasons that species become extinct. Distinguish natural causes, such as changes in the climate and continents, from human causes, such as overhunting and habitat destruction.

Have students prepare posters showing endangered species in their habitats. In companion reports, students should list possible reasons why the species is becoming extinct and ways to help save it.

Have your class identify changes in the natural environment that people have made on the school grounds (laying down pavement, chopping down trees, putting up telephone wires, and so on). Ask them how these changes might have affected animals and their habitats. Let students compare two photographs of the same local site taken several years apart to identify changes that have occurred as a result of human or natural causes.

The Road They Traveled
Most scientists agree that North America was originally populated by people from Asia who traveled across Beringia. Beringia encompassed the area where the Bering Sea is today. During the late part of the last Ice Age, called the Pleistocene epoch, much of the Earth's water was frozen in glaciers. This lowered the sea level approximately 50 meters, exposing a land bridge near the Arctic Circle. This area, which we call the Bering Land Bridge, connected Asia and North America. Paleoindians most likely used this route to move between North America and Asia.

Have students locate the Bering Strait on a map. Then ask them to suggest other possible routes by which prehistoric humans might have journeyed from Asia to North America. Formulate the suggested possible routes into testable hypotheses, such as, "If remnants of watercraft dating to the Paleoindian time are found across the South Pacific and the Western Hemisphere, then we can accept the hypothesis that early people in the New World could have migrated via watercraft across the South Pacific."

During a study of climates, discuss the types of events that cause climatic change. Natural changes include volcanic eruptions, the amount of energy released by the sun, and the Earth's tilt. Changes caused by human activity include the burning of fossil fuels and destruction of forests.

Map Relief
What would the shoreline of North America look like if global warming caused the ice caps in Greenland and Antarctica to melt? Let students create a relief map of the United States (or possibly all of the continents) with modeling clay. (See the "Resources" page, for a recommended reference map. ) Mount your clay relief map on a thick sheet of plastic foam or on some other type of platform. Place the mounted relief map on the floor of a plastic wading pool or other large container. Place large blocks of ice in the "polar" regions and then fill the pool with water until it reaches the base of the map. Ask students to hypothesize how the shoreline of the continents would change if ocean levels rose as a result of melting ice caps. What would happen to peninsulas and islands? Observe the clay relief map as the ice melts.

How's The Weather In There?
To help students understand the "greenhouse effect," (how heat is trapped in the Earth's atmosphere) have them make a simple greenhouse using a clear plastic storage box with lid (commonly sold for shoe storage). Fill the bottom of the box with three centimeters of soil. Prop a thermometer in the center with the bulb facing up. Mount a heat lamp 30 centimeters overhead. Expose the open box to the heat lamp for 10 minutes, record the temperature immediately, and then allow the greenhouse to return to room temperature. Put the lid on the greenhouse. Turn on the heat lamp for 10 minutes and again record the temperature. Which time was the temperature higher? Why? (The temperature should be higher in the closed box, because the radiation, which changed to heat, could not escape.)

Artifacts Of The Future
An artifact is any object made, used, or modified by people. Artifacts reveal information about a society's values, practices, and technological skills.

Divide the class into four groups. Imagine that an archaeological dig is in progress a thousand years from now at the site of your school. Together, make a list of artifacts that might be uncovered. For each artifact, have students write a brief description of what the piece might tell archaeologists about the school and class members. Here are a few of the questions you might consider: What is the item's function? How old is it? What raw materials were used to make it? What is the source of these raw materials? What technology was used to make it? What do images or writing on the object suggest about the values of the people who made it? Consider those artifacts that would not be unearthed because of natural decay. How might the absence of these objects affect what scientists of the future conclude about activities at the school?