Lesson Plan: Development of a Habitable Planet

1. Ask students to think about the origin of Earth. Working alone or in pairs, have students explore the Infrared Search for Origins Flash Interactive , focusing on the "Star Formation" and "Planetary Systems" sections.

2. Divide the class into 10 groups and hand each group an index card with the name of an event. Explain that each group will conduct their own research for their assigned event and that they should be prepared to discuss their findings with the class. You may want to remind them that the answers are not always clearly defined. They should be able to answer, to the best of their ability:

1. The conditions prior to the event
2. The event itself: What happened? What caused it? When and how did it happen?
3. The conditions after the event and its impact on the future of Earth

3. Before having the students disperse to do their research, show the class the following video segments to introduce them to some history of the evolution of Earth and life. These videos do not directly relate to one another and do not have to be shown in order - use as time allows. As students watch the video segments, ask them to record one thing that they learned from each video and one thing that they would like to find out more about. If there is time, have students share their thoughts with the class.

1. The Elements: Forged in Stars QuickTime Video explains the role of stars in creating the elements found on Earth and throughout the universe.
2. The Origin of the Moon QuickTime Video shows how samples of rock from the Moon led scientists to theorize that the Moon was formed from Earth materials.
3. Jupiter: Earth's Shield QuickTime Video shows how Jupiter's gravity has protected Earth and why scientists are looking for a similar planetary setup for extrasolar planets.
4. Global Warming: The Physics of the Greenhouse Effect QuickTime Video explains how the greenhouse effect works on Earth and how humans are affecting it.
5. Ingredients for Life: Water QuickTime Video demonstrates the importance of water to life and explores the possibilities for extreme forms of life.
6. Life Before Oxygen QuickTime Video explains how our once oxygen-free atmosphere changed dramatically when primitive bacteria evolved the capacity to harness solar energy through photosynthesis, which produced oxygen as a by-product. Thought-provoking questions are included in the resource and should help students grasp the enormity of this development.

4. Have students study the following interactive resources: Deep Time Flash Interactive and The Wall of Time JPEG Image . Both resources present a detailed, interactive timeline of events. They will help the students develop an understanding of their event and how it fits in with geologic time.

5. Have each group present its findings. Using the information they have gathered as a class, students should be able to piece together their own geologic timeline without help from the instructor. This can be done with students standing in front of the room and arranging themselves in the correct order, or by taping a representation of their event on a timeline wall in the classroom.

Because of the complexity of these events and the interpretation of evidence, there may be several different "correct" versions of the timeline that the students create. Those who have collected the most evidence and have the most persuasive arguments may dictate the final result.

6. Ask students to consider the seemingly unique conditions on Earth. Allow time at the computers to look at the Life's Little Essential: Liquid Water HTML Document , the Mars Dead or Alive: Mars Up Close Flash Interactive , the The Search for Another Earth Flash Video , and the Caves: Extreme Conditions for Life QuickTime Video . Discuss the following:

1. Why do most scientists think that water is necessary for life to exist?
2. How did the discovery of extremophiles change views about life?
3. Do you think that it is possible for life to exist on Mars?
4. Do you think that there are other habitable planets in the universe? What about habitable moons?
5. Did you find any answers to the questions that you had posed when watching the video segments earlier (in step 3)? Which of your questions did these resources answer?

7. Lead a debate about the search for extraterrestrial life. Now that we understand that there are billions of galaxies in the universe, with hundreds of billions of stars in each, it seems quite probable that there may be other life or other planets similar to Earth. And now that we have found extreme forms of life in places on Earth that were previously thought unlivable, it seems possible that life may be thriving in other non-Earthlike worlds.

1. Divide the class into teams for and against further research to answer the question of whether or not humans are alone in the universe.
2. Issues to address may include the following: the timescale for life to develop, the limitations of space exploration, the conditions necessary for life, methods to search for life as we know it, methods to look for life NOT as we know it, and the search for extraterrestrial intelligence.