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Guidepost

This chapter is either unnecessary or vital. If you believe that astronomy is the study

of the physical universe above the clouds, then you are done; the previous 25 chapters

completed your study of astronomy. But, if you believe that astronomy is the study not

only of the physical universe but also of your role as a living being in the evolution of

the universe, then everything you have learned so far from this book has been prepara-

tion for this fi nal chapter.

As you read this chapter, you will ask four important, related questions:

What is life?

How did life originate on Earth?

Could life begin on other worlds?

Can humans on Earth communicate with civilizations on other worlds?

You won’t get more than the beginnings of answers to those questions here, but often in

science asking a question is more important than getting an immediate answer.

You have explored the universe from the phases of the moon to the big bang, from

the origin of Earth to the death of the sun. Astronomy is meaningful, not just because

it is about the universe but because it is also about you. Now that you know astronomy,

you see yourself and your world in a different way. Astronomy has changed you.

Single amino acids can be

assembled into long

proteinlike molecules.

When such material cools

in water, it often forms

microspheres, tiny

globules with double-

layered boundaries similar

to cell membranes.

Microspheres may have

been an intermediate

stage in the evolution of

life between complex but

nonliving molecules and

living cells holding

molecules reproducing

genetic information.

(Sidney Fox and Randall Grubbs)

Astrobiology: Life on

26 Other Worlds