21st Century Astronomy

Laura Kay, Stacy Palen, George Blumenthal

Chapter 24

Life - all with Video Answers

Educators

Chapter Questions

Problem 1

The study of life and the study of astronomy are connected because (select all that apply)
a. life may be commonplace in the universe.
b. studying other planets may help explain why there is life on Earth.
c. explorations of extreme environments on Earth suggest where to look for life elsewhere.
d. life is a structure that evolved through physical processes, and life on Earth may not be unique.
e. life elsewhere is most likely to be found by astronomers.

Sarah Mccrumb

Sarah Mccrumb

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Problem 2

Scientists look for water to indicate places where life might exits because
a. water is a common molecule in interstellar space.
b. life on Earth depends on it.
c. no other molecules are solvents.
d. the spectrum of water is very complex.

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Problem 3

The Urey-Miller experiment produced _________ in a laboratory jar.
a. life
b. RNA and DNA
c. amino acids
d. proteins

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Problem 4

A mutation is
a. always a deadly change to DNA.
b. always a beneficial change to DNA.
c. a change to DNA that is sometimes beneficial and sometimes not.
d. a change to DNA that is not inheritable.

Sarah Mccrumb

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Problem 5

Scientists think that terrestrial life probably originated in Earth's oceans, rather than on land, because (select all that apply
a. all the chemical pieces were in the ocean.
b. energy was available in the ocean.
c. the earliest evidence for life on Earth is from fossils of ocean-dwelling organisms.
d. the deepest parts of the ocean have hydrothermal vents.

Sarah Mccrumb

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Problem 6

Any system with the processes of heredity, mutation, and natural selection will (choose all that apply)
a. change over time.
b. become larger over time.
c. become more complex over time.
d. develop intelligence.

Sarah Mccrumb

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Problem 7

The fact that no alien civilizations have yet been detected indicates that
a. they are not there.
b. they are rare.
c. Earth is in a "blackout," and they are not talking to us.
d. we don't know enough yet to draw any conclusions.

Sarah Mccrumb

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Problem 8

During the Cambrian explosion
a. the dinosaurs were killed.
b. all the carbon that is now here on Earth was produced.
c. biodiversity increased significantly.
d. a lot of carbon dioxide was released into the atmosphere.

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Problem 9

The habitable zone is the place around a star where
a. life has been found.
b. atmospheres can contain oxygen.
c. liquid water exists.
diquid water can exist on the surface of a planet.

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Problem 10

The difference between a prokaryote and a eukaryote is that prokaryotes
a. have no DNA.
b. have no cell wall.
c. have no nucleus.
d. do not exist today.

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Problem 11

A thermophile is an organism that lives in extremely __________ environments.
a. salty
b. hot
c. cold
d. dry

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Problem 12

The search for life elsewhere in the Solar System is carried out primarily by
a. astronauts.
b. robotic spacecraft.
c. astronomers using optical telescopes.
d. astronomers using radio telescopes.

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Problem 13

Astronomers think that intelligent life is more likely to be found around stars of types $\mathrm{F}, \mathrm{G}, \mathrm{K},$ and $\mathrm{M}$ because
a. those stars are hot enough to have planets and moons with liquid water.
b. those stars are cool enough to have planets and moons with liquid water
c. those stars live long enough for life to begin and evolve.
d. those stars produce no ultraviolet radiation or X-rays.

Sarah Mccrumb

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Problem 14

Life first appeared on Earth
a. billions of years ago.
b. millions of years ago.
c. hundreds of thousands of years ago.
d. thousands of years ago.

Sarah Mccrumb

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Problem 15

In the phrase "theory of evolution," the word theory means that evolution
a. is an idea that can't be tested scientifically.
b. is an educated guess to explain natural phenomena.
c. probably doesn't happen anymore.
d. is a tested and corroborated scientific explanation of natural phenomena.

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Problem 16

How does the evolution of life on Earth depend on RNA and DNA?

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Problem 17

How do scientists think that amino acids first formed on Earth?

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Problem 18

Today, most organisms on Earth enjoy relatively moderate climates and temperatures. Compare this environment to some of the conditions in which early life developed

Sarah Mccrumb

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Problem 19

In the Process of Science Figure, many areas of science are represented that all inform the science of astrobiology. Choose any two of these, and explain how one of these areas of science depends on the other.

Sarah Mccrumb

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Problem 20

How was Earth's carbon dioxide atmosphere changed into today's oxygen-rich atmosphere? How long did that transformation take?

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Problem 21

What was the Cambrian explosion, and what might have caused it?

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Problem 22

Why did plants and forests appear in high numbers before large animals did?

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Problem 23

What is a habitable zone? What defines its boundaries?

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Problem 24

Which general conditions were needed on Earth for life to arise?

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Problem 25

Is evolution under way on Earth today? If so, how might humans continue to evolve?

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Problem 26

Where did all the atoms in your body come from?

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Problem 27

The two Viking spacecraft did not find convincing evidence of life on Mars when they visited that planet in the late 1970 s nor did the Phoenix lander when it examined the martian soil
in $2009 .$ Do these results imply that life never existed on the planet? Why or why not?

Sarah Mccrumb

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Problem 28

Some scientists believe that humans may be the only advanced life in the galaxy today. If this is indeed the case, which factors in the Drake equation must be extremely small?

Sarah Mccrumb

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Problem 29

The second law of thermodynamics says that the entropy (a measure of disorder) of the universe is always increasing. Yet complex living organisms exist. Why does this not violate the second law of thermodynamics?

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Problem 30

Why is it likely that life on Earth as we know it will end long before the Sun runs out of nuclear fuel?

Sarah Mccrumb

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Problem 31

The Kepler Mission is currently searching for planets in the habitable zones of stars. Explain which factors in the Drake equation are affected by this search and how the final number $N$ will be affected if Kepler finds that most stars have planets in their habitable zones.

Sarah Mccrumb

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Problem 32

Study Figure $24.18 .$ The white blocks at the top represent the numbers 1-10. The bottom row of the set is a placeholder, and the top three rows of the set represent the numbers, in order from left to right. Explain the "rule" for the kind of counting shown here. (For example, how do three white blocks represent the number $7 ?$

Dading Chen

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Problem 33

Suppose that an organism replicates itself each second. If you start with a single specimen, what will the final population be after 10 seconds?

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Problem 34

Suppose that an organism replicates itself each second. After how many seconds will the population increase by a factor of $1,024 ?$

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Problem 35

As a general rule, you can find the doubling time for exponential growth by dividing 70 by the rate of increase. So, if the population increases by 7 percent per year, the doubling time is 10 years $(70 / 7=10) .$ Suppose Earth's human population continues to grow by 1 percent annually. What is the doubling time? How much time will pass before there are 4 times as many humans on Earth?

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Problem 36

As discussed in Working It Out 24.1 , the doubling time for exponential growth is given by $P_{\mathrm{F}} / P_{\mathrm{O}}=2^{n}$. Assume a self-replicating molecule that makes one copy of itself each second. Make a graph of the number of molecules versus time for the first 60 seconds after the molecule begins replicating.

Sarah Mccrumb

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Problem 37

The doubling time for Escherichia coli is 20 minutes, and you start getting sick when just 10 bacteria enter your system. How many bacteria are in your body after 12 hours?

Sarah Mccrumb

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Problem 38

If the chance that a given molecule will mutate is one in $100,000,$ how many generations are needed before, on average, at least one mutation has occurred?

Sarah Mccrumb

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Problem 39

Study the Drake equation in Working It Out $24.2 .$ Make your own most optimistic and most pessimistic assumptions for each of the variables in the equation. What values do you find for $N ?$

Dading Chen

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Problem 40

Study the Drake equation in Working It Out $24.2 .$ Keep the other variables as is, but put in different values for the lifetime of a technological civilization. How does this affect your value of $N ?$ How does this affect the possibility of making contact with extraterrestrials?

Dading Chen

Numerade Educator

Problem 41

Look back at Figure 5.24 in Chapter $5 .$ Trace (or photocopy) this graph, and then add horizontal lines for the temperatures at which water freezes and boils. Which planets in the Solar System have measured temperatures that fall within those lines? Which planets have predicted temperatures (based on the equilibrium model) that fall within those lines? What does this tell you about assumptions about the habitable zone?

Daniel Azubuike

Daniel Azubuike

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Problem 42

Figure 5.24 shows that Mercury's measured range of temperatures overlaps the temperatures at which water is a liquid. Is Mercury in the habitable zone? Why or why not?

Sarah Mccrumb

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Problem 43

Suppose astronomers announce the discovery of a new planet around a star with a mass equal to the Sun's. This planet has an orbital period of 87 days. Is this planet in the habitable zone for a Sun-like star?

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Problem 44

Why do you think astronomers sent a coded radio signal to the globular cluster $\mathrm{M} 13$ in $1974-$ rather than, say, to a nearby star?

Sarah Mccrumb

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Problem 45

As noted in Section 24.1 , some scientists suspect the early Earth was "seeded" with primitive life stored in comets and meteoroids. Knowing when and how our Solar System, galaxy, and universe formed, what timeline is required for such seeding to be possible?

Sarah Mccrumb

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Problem 46

a. Go to the online Astrobiology Magazine (http://astrobio.net), which covers many topics included in this chapter. Under “Origins," click on "Extreme Life." What are some new findings about extremophiles? Why is this important for astrobiologists? Under "Deep Space" click on "New Planets." What is a recent discovery?
b. Go to the "Life, Unbounded" blog (http://blogs.scientificamerican.com/life-unbounded). What is a recent topic of interest? Is the discussion based on some new data? A new theory?

Sana Riaz

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Problem 47

Solar System space missions:
a. Go to the website for the Cassini mission to Saturn (http://saturn.jpl.nasa.gov). Is it still collecting data? What has been found recently on one of the moons that would be of interest to astrobiologists?
b. Go to the website for the Mars Science Laboratory (http://mars.jpl.nasa.gov/msl/mission). The rover Curiosity landed on the surface in $2012 .$ What are the science goals of this mission, and how do they relate to astrobiology? What are some recent results?
c. The $M A V E N$ Mars mission (http://mars.nasa.gov/maven/) arrived at Mars in $2014 .$ What are the science goals of this mission? Why are astrobiologists interested in the history of the climate and atmosphere of Mars? Are there any results?

Rodger Claar

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Problem 48

Go to the "Habitable Exoplanets Catalog" website (http://phl .upredu/projects/habitable-exoplanets-catalog). Click on "Methods" to read about the different criteria for evaluating a planet's habitability. How many confirmed habitable exoplanets are there? How many candidates? How might the number of confirmed exoplanets affect the terms in the Drake equation?

Sarah Mccrumb

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Problem 49

a. Go to the website for the Kepler space telescope (http://kepler.nasa.gov): click on "News" and "Planetfinding News." What is a recent discovery of a planet in the habitable zone? What is a recent discovery of a planet with an interesting atmosphere?
b. Go to the website for the European Space Agency (ESA) Gaia mission (http://sci.esa.int/gaia). What are the science objectives of this mission? Click on "Exoplanets" on the left. How will Gaia identify new planets? What properties of the planet will it be able to measure? What are some recent results?

Alex Bretton

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Problem 50

Go to the website for "Super Planet Crash" (http://www stefanom.org/spc/). Start with an "Earth" in the habitable zone and start adding in other planets. Does the system remain stable if you add in a second planet to the habitable zone? What happens if you add a third planet? What happens if you add planets inside or outside of the habitable zone?

Alex Bretton

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