Infrared Search for Origins
Ingredients for Life: Water
Jupiter: Earth's Shield
Life Before Oxygen
Life's Little Essential: Liquid Water
Mars Dead or Alive: Mars Up Close
The Origin of the Moon
The Wall of Time
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Earth is just one of innumerable objects in the universe, but it is the only object known to be able to support life. How did the planet Earth develop into the life- bearing planet that it is today? Is it possible that other habitable worlds have also developed? In this lesson, students investigate the origin of the elements, the process of planet formation, the evolution of life on Earth, and the conditions necessary for life as we know it. Students research particular events in the history of Earth that have led to its present state, synthesize their findings with the class, and contemplate the rarity of habitable planets.
Two to three class periods
10 index cards
If possible, arrange computer access for all students to work individually or in pairs. Write each of the following events on an index card:
1. Ask students to think about the origin of Earth. Working alone or in pairs, have students explore the Infrared Search for Origins 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:
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.
4. Have students study the following interactive resources: Deep Time Interactive and The Wall of Time 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 Document, the Mars Dead or Alive: Mars Up Close Interactive, and the Caves: Extreme Conditions for Life Video. Discuss the following:
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.
Have students discuss the following:
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.