1. Universe Tenth Edition Chapter 27 The Search for Extraterrestrial Life Roger Freedman Robert Geller William Kaufmann III

3. 27-1 How comets and meteorites could have aided the origin of life on Earth 27-2 On which other worlds of our solar system life might have evolved 27-3 About the controversy over proposed fossil life from Mars 27-4 How astronomers estimate the number of other civilizations in the Galaxy 27-5 Why radio telescopes may be a useful tool for contacting alien civilizations 27-6 How astronomers hope to detect Earthlike planets orbiting other stars By reading this chapter, you will learn

4. Complex Molecules and Carbon 27-1: The chemical building blocks of life are found in space

5. Why Silicon is Unsuitable for Making Living Organisms

6. A Carbonaceous Chondrite

7. An Updated Miller-Uray Experiment

8. Extremophiles Can Take the Heat 27-2: Water and the potential for life

9. Extremophiles Can Take the Heat

10. Subsurface Ocean on Enceladus

11. Exploring Lake Vostok

12. Digging in the Martian Surface

13. A “Face” on Mars?

15. A Meteorite from Mars 27-3: Meteorites from Mars have been scrutinized for life forms

16. A Meteorite from Mars

17. Microscopic Tunnels In Martian Meteorite

18. Habitable Zones for Life

19. The Water Hole 27-5: Radio searches for alien civilizations are underway

20. 27-6: Telescopes have been searching for Earthlike planets The Infrared Spectrum of a Simulated Planet

22. Key Ideas Organic Molecules in the Universe: All life on Earth, and presumably on other worlds, depends on organic (carbon-based) molecules. These molecules occur naturally throughout interstellar space. The organic molecules needed for life to originate were probably brought to the young Earth by comets,meteorites and interplanetary dust particles. Another likely source for organic molecules is chemical reactions in the Earth ’ s primitive atmosphere. Similar processes may occur on other worlds.

23. Key Ideas Life in the Solar System: Besides Earth, other worlds in our solar system—the planet Mars, Jupiter ’ s satellite Europa, and Saturn’s satellite Enceladus—may have had the right conditions for the origin of life. Europa appears to have extensive liquid water beneath its icy surface. Future missions may search for the presence of life there. Enceladus also appears to contain a large subsurface ocean, and some of this material is ejected through ice volcanoes for easier sampling. Mars once had liquid water on its surface, though it has none today. Life may have originated on Mars during the liquid water era.

24. Key Ideas The Viking Lander spacecraft searched for microorganisms on the Martian surface, but found no conclusive sign of their presence. The Mars Science Laboratory is designed to assess the past and present suitability of Mars for microbial life. An ancient Martian rock that came to Earth as a meteorite shows features that have been suggested as remnants of Martian life. Most of these features can be explained by geologic processes.

25. Key Ideas Radio Searches for Extraterrestrial Intelligence: Astronomers have carried out a number of searches for radio signals from other stars. No signs of intelligent life have yet been detected, but searches are continuing and using increasingly sophisticated techniques. The Drake equation is a tool for estimating the number of intelligent, communicative civilizations in our Galaxy. Telescope Searches for Earthlike Planets: A future generation of orbiting telescopes may be able to detect numerous terrestrial planets around nearby stars. If such planets are found, their infrared spectra may reveal the presence or absence of life.