Listen & Learn: The Shadow Biosphere

Learn why alien life might exist on Earth

Pre-listening vocabulary

• sustain: to support something for a long time
• potential: the possibility to do or become something
• microbe: a small living thing, like a bacterium or virus
• thrive: to live and grow well in a certain environment
• essential: necessary, very important
• hypothesis: an idea that is currently unproven
• habitable: able to support life

Listening activity

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Gapfill exercise

The biosphere is all of the areas on Earth that can sustain life. Most complex plants and animals need lots of , oxygen, and sunlight to survive. When scientists look for life on other , they seek places that have the potential to provide these things. On Earth, however, certain microbes thrive in that are low in these essential ingredients. These microbes are called extremophiles. They live in volcanoes, , and Antarctic ice. Some extremophiles survive because they can use unusual chemicals to sustain themselves. It is possible that Earth contains microbes with chemical structures that are very different from our own. This hypothesis is called the “shadow biosphere.” A shadow biosphere would be made up of life that is chemically unrelated to life as we know it. If this type of life , there may be more habitable planets than we think.

Comprehension questions

See answers below

1. The biosphere is
   a. the surface of the Earth, where there is plenty of light and oxygen
   b. the areas of the Earth where most plants and animals live
   c. all of the areas on Earth that can sustain life
   
2. Microbes that can live in environments without much water, sunlight, or oxygen are called
   a. eukaryotes
   b. extremophiles
   c. eubacteria
   
3. The “shadow biosphere” hypothesis suggests that
   a. life on other planets is probably very similar to life on Earth
   b. new types of bacteria are evolving very quickly underground
   c. Earth may contain microbes that have very different chemical structures from us

Discussion/essay questions

1. Do you believe in life on other planets? Why or why not? Why do you think we haven’t found any?

Transcript

The biosphere is all of the areas on Earth that can sustain life. Most complex plants and animals need lots of water, oxygen, and sunlight to survive. When scientists look for life on other planets, they seek places that have the potential to provide these things. On Earth, however, certain microbes thrive in environments that are low in these essential ingredients. These microbes are called extremophiles. They live in volcanoes, deserts, and Antarctic ice. Some extremophiles survive because they can use unusual chemicals to sustain themselves. It is possible that Earth contains microbes with chemical structures that are very different from our own. This hypothesis is called the “shadow biosphere.” A shadow biosphere would be made up of life that is chemically unrelated to life as we know it. If this type of life exists, there may be more habitable planets than we think.

Answers to comprehension questions

1c 2b 3c