30 (1)

Question 1

we will consider how life began on Earth, whether the same processes could have led to life on other worlds, and how we might seek evidence of life elsewhere. This is the science of ……………

Scientists today take a multidisciplinary approach to studying the origin, evolution, distribution, and ultimate fate of life in the universe; this field of study is known as ……………….

Answer 1

astrobiology

Question 2

We saw that the universe was born in the Big Bang about …….. ………. years ago.

Answer 2

14 billion

Question 3

Big bang

After the initial hot, dense fireball of creation cooled sufficiently for ……….. to exist, all matter consisted of ………… and ………… (with a very small amount of …………).

Answer 3

atoms

hydrogen / helium / lithium

Question 4

Big Bang

As the universe aged, processes within stars created the other elements, including:

those that make up Earth (such as …………………4)

and

those required for life as we know it, such as …………………… 3.

Answer 4

iron, silicon, magnesium, and oxygen

carbon, oxygen, and nitrogen

Question 5

In particular, life on Earth is based on the presence of a key unit known as an …………. molecule, a molecule that contains …………..

Especially important are the …………, chemical compounds made up entirely of ………….. and …………, which serve as the basis for our biological chemistry, or ………….

Answer 5

organic / carbon

hydrocarbons / hydrogen / carbon / biochemistry

Question 6

While we do not understand the details of how life on Earth began, it is clear that to make creatures like us possible, events like the ones we described must have occurred, resulting in what is called the ……….. ……….. of the universe.

Answer 6

chemical evolution

Question 7

mammals may owe their domination of Earth’s surface to just such a collision ………. ……… years ago, which led to the extinction of the dinosaurs (along with the majority of other living things).

Answer 7

65 million

Question 8

……………..—planets orbiting around other stars, from huge ones orbiting close to their stars (informally called “hot Jupiters”) down to planets smaller than Earth.

Answer 8

exoplanets

Question 9

Philosophers of science sometimes call the idea that there is nothing special about our place in the universe the ………… ………… Given all of the above, most scientists would be surprised if life were limited to our planet and had started nowhere else.

Answer 9

Copernican principle

Question 10

Faced with such a prospect, physicist ………. ………. asked a question several decades ago that is now called the ……….. ………..: where are they? If life and intelligence are common and have such tremendous capacity for growth, why is there not a network of galactic civilizations whose presence extends even into a “latecomer” planetary system like ours?

Answer 10

Enrico Fermi

Fermi paradox

Question 11

Meteorites have been found to contain two kinds of substances whose chemical structures mark them as having an extraterrestrial origin—…………………..

Answer 11

amino acids and sugars

Question 12

Since the early 1950s, scientists have tried to duplicate in their laboratories the chemical pathways that led to life on our planet. In a series of experiments known as the ………… ……….., pioneered by ……… ……….. and ………. ………… at the University of Chicago, biochemists have simulated conditions on early Earth and have been able to produce some of the fundamental building blocks of life, including those that form proteins and other large biological molecules known as ……… ……..

Answer 12

Miller-Urey experiments / Stanley Miller / Harold Urey / nucleic acids

Question 13

…………. ………..—seafloor systems in which ocean water is superheated and circulated through crustal or mantle rocks before reemerging into the ocean—have also been suggested as potential contributors of organic compounds on the early Earth, and such sources would not require Earth to have an early reducing atmosphere.

Answer 13

Hydrothermal vents

Question 14

you learned that Earth was subjected to a heavy bombardment—a period of large impact events—some ………. to ……… ………. years ago. Large impacts would have been energetic enough to heat-sterilize the surface layers of Earth, so that even if life had begun by this time, it might well have been wiped out.

Answer 14

3.8 / 4.1 / billion

Question 15

When the large impacts ceased, the scene was set for a more peaceful environment on our planet. If the oceans of Earth contained accumulated organic material from any of the sources already mentioned, the ingredients were available to make living organisms. We do not understand in any detail the sequence of events that led from molecules to biology, but there is fossil evidence of microbial life in 3.5-billion-year-old rocks, and possible (debated) evidence for life as far back as 3.8 billion years.

Answer 15

R 2

Question 16

the most primitive life required two special capabilities:

1. a means of extracting ……….. from its environment,
2. and a means of ……….. and ……….. information in order to make faithful copies of itself.

Answer 16

1. energy
2. encoding / replicating

Question 17

Life as we know it employs two main molecular systems:

1. the functional molecules known as …………, which carry out the chemical work of the cell,
2. and information-containing molecules of …………….. that store information about how to create the cell and its chemical and structural components.

Answer 17

1. proteins
2. DNA (deoxyribonucleic acid)

Question 18

The origin of life is sometimes considered a “chicken and egg problem” because, in modern biology, neither of these systems works without the other. It is our proteins that assemble DNA strands in the precise order required to store information, but the proteins are created based on information stored in DNA. Which came first?

Answer 18

R 2

Question 19

Some origin of life researchers believe that prebiotic chemistry was based on molecules that could both store information and do the chemical work of the cell. It has been suggested that ……….. …………, a molecule that aids in the flow of genetic information from DNA to proteins, might have served such a purpose. The

Answer 19

RNA (ribonucleic acid)

Question 20

the increase in atmospheric levels of oxygen about ……… ……… years ago means that oxygen-producing photosynthesis must have emerged and become globally important by this time. In fact, it is likely that oxygen-producing photosynthesis emerged considerably earlier.

Answer 20

2.4 billion

Question 21

If a second example of life is found in our solar system or a nearby star, it would imply that life emerges commonly enough that the universe is likely filled with biology. To make such observations, however, we must first decide where to focus our search.

Answer 21

Understanding what conditions and features make a habitable environment is important both for understanding how widespread habitable environments may be in the universe and for focusing a search for life beyond Earth.

Question 22

Life requires a solvent (a liquid in which chemicals can dissolve) that enables the construction of biomolecules and the interactions between them. For life as we know it, that solvent is …………, which has a variety of properties that are critical to how our biochemistry works.

Answer 22

water

Question 23

life requires that water be in liquid form (rather than ice or gas). Identifying environments where water is present within the appropriate range of temperature and pressure is thus an important first step in identifying habitable environments.

Answer 23

R 2

Question 24

Our biochemistry is based on molecules made of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. …………. is at the core of organic chemistry. Its ability to form four bonds, both with itself and with the other elements of life, allows for the formation of a vast number of potential molecules on which to base biochemistry.

Answer 24

Carbon

Question 25

These “biogenic elements,” sometimes referred to with the acronym …………….. (………………6), are the raw materials from which life is assembled, and an accessible supply of them is a second requirement of habitability.

Answer 25

CHNOPS

carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur