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The densest part of planet Earth is the | (A) continental crust (B) oceanic crust (C) core (D) mantle | C | When Earth was entirely molten, gravity drew denser elements to the center and lighter elements rose to the surface. The separation of Earth into layers based on density is known as differentiation. The densest material moved to the center to create the planets dense metallic core. Materials that are intermediate in density became part of the mantle (Figure 1.1). |
water in the gaseous state | (A) atmosphere (B) nuclear fusion (C) comet (D) solar nebula (E) water vapor (F) Kuiper belt (G) oxygen | E | The photo above represents water in three common states of matter. States of matter are different phases in which any given type of matter can exist. There are actually four well-known states of matter: solid, liquid, gas, and plasma. Plasma isnt represented in the iceberg photo, but the other three states of matter are. The iceberg itself consists of water in the solid state, and the lake consists of water in the liquid state. Q: Where is water in the gaseous state in the above photo? A: You cant see the gaseous water, but its there. It exists as water vapor in the air. Q: Water is one of the few substances that commonly exist on Earth in more than one state. Many other substances typically exist only in the solid, liquid, or gaseous state. Can you think of examples of matter that usually exists in just one of these three states? A: Just look around you and you will see many examples of matter that usually exists in the solid state. They include soil, rock, wood, metal, glass, and plastic. Examples of matter that usually exist in the liquid state include cooking oil, gasoline, and mercury, which is the only metal that commonly exists as a liquid. Examples of matter that usually exists in the gaseous state include oxygen and nitrogen, which are the chief gases in Earths atmosphere. |
The Sun formed from | (A) a spinning cloud of gas and dust (B) large dense planets pulled to the center by gravity (C) radioactive dust that ignited (D) a collision by two stars | A | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure |
When the solar system first formed | (A) life forms were primitive (B) asteroid impacts were common (C) each planets was surrounded by a thick atmosphere (D) all of these | B | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. |
gas missing from Earths early atmosphere | (A) atmosphere (B) nuclear fusion (C) comet (D) solar nebula (E) water vapor (F) Kuiper belt (G) oxygen | G | Earths first atmosphere was made of hydrogen and helium, the gases that were common in this region of the solar system as it was forming. Most of these gases were drawn into the center of the solar nebula to form the Sun. When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. High heat in Earths early days meant that there were constant volcanic eruptions, which released gases from the mantle into the atmosphere (see opening image). Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions. Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system (Figure Calculations also show that asteroids and comets cannot be responsible for all of the gases of the early atmosphere, so both impacts and outgassing were needed. |
reaction in which hydrogen atoms change to helium | (A) atmosphere (B) nuclear fusion (C) comet (D) solar nebula (E) water vapor (F) Kuiper belt (G) oxygen | B | Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. Thats because a great deal of energy is needed to overcome the force of repulsion between positively charged nuclei. The suns energy comes from fusion in its core, where temperatures reach millions of Kelvin (see Figure 11.16). |
Gases in the first atmosphere came from | (A) comet impact (B) volcanic outgassing (C) none of these (D) both of these | D | Earths first atmosphere was different from the current one. The gases came from two sources. Volcanoes spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere (Figure 12.5). Take a look at the list of gases. Whats missing? The early atmosphere had almost no oxygen. |
giant cloud of gas and dust from which the solar system formed | (A) atmosphere (B) nuclear fusion (C) comet (D) solar nebula (E) water vapor (F) Kuiper belt (G) oxygen | D | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure |
gases that surround a planet | (A) atmosphere (B) nuclear fusion (C) comet (D) solar nebula (E) water vapor (F) Kuiper belt (G) oxygen | A | An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not stable. |
The solar system formed from a giant mass of gas and dust. | (A) true (B) false | A | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure |
The sun formed billions of years before other objects in the solar system. | (A) true (B) false | B | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. |
The solar nebula formed a disk before it formed the sun. | (A) true (B) false | A | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure |
The first atmosphere contained nitrogen, carbon dioxide, oxygen, and hydrogen. | (A) true (B) false | B | Earths first atmosphere was different from the current one. The gases came from two sources. Volcanoes spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere (Figure 12.5). Take a look at the list of gases. Whats missing? The early atmosphere had almost no oxygen. |
Objects in our solar system include dwarf planets. | (A) true (B) false | A | The dwarf planets of our solar system are exciting proof of how much we are learning about our solar system. With the discovery of many new objects in our solar system, astronomers refined the definition of a dwarf planet in 2006. According to the IAU, a dwarf planet must: Orbit a star. Have enough mass to be nearly spherical. Not have cleared the area around its orbit of smaller objects. Not be a moon. |
All of the stars in the Universe formed at around the same time as our Sun. | (A) true (B) false | B | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. |
As Earth formed, gravity pulled lighter materials to the center of the planet. | (A) true (B) false | B | When Earth was entirely molten, gravity drew denser elements to the center and lighter elements rose to the surface. The separation of Earth into layers based on density is known as differentiation. The densest material moved to the center to create the planets dense metallic core. Materials that are intermediate in density became part of the mantle (Figure 1.1). |
Earths mantle is made entirely of liquid rock. | (A) true (B) false | B | The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. |
The Sun, planets and other solar system objects formed at about the same time. | (A) true (B) false | A | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. |
There was a lot of space debris in the early solar system. | (A) true (B) false | A | Hundreds of thousands of asteroids have been found in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month! The majority are located in between the orbits of Mars and Jupiter. This region is called the asteroid belt, as shown in Figure 25.32. There are many thousands of asteroids in the asteroid belt. Still, their total mass adds up to only about 4 percent of Earths Moon. Asteroids formed at the same time as the rest of the solar system. Although there are many in the asteroid belt, they were never were able to form into a planet. Jupiters gravity kept them apart. |
Early Earth was much like Earth today. | (A) true (B) false | B | Since the early Earth was very hot, mantle convection was very rapid. Plate tectonics likely moved very quickly. The early Earth was a very active place with abundant volcanic eruptions and earthquakes. The remnants of these early rocks are now seen in the ancient cores of the continents. |
Before there was an ocean, there was water vapor in the atmosphere. | (A) true (B) false | A | The early atmosphere was rich in water vapor from volcanic eruptions and comets. When Earth was cool enough, water vapor condensed and rain began to fall. The water cycle began. Over millions of years enough precipitation collected that the first oceans could have formed as early as 4.2 to 4.4 billion years ago. Dissolved minerals carried by stream runoff made the early oceans salty. What geological evidence could there be for the presence of an early ocean? Marine sedimentary rocks can be dated back about 4 billion years. By the Archean, the planet was covered with oceans and the atmosphere was full of water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases. Click image to the left or use the URL below. URL: |
Earths moon began as a dwarf planet orbiting the sun. | (A) true (B) false | B | Material at a similar distances from the Sun collided together to form each of the planets. Earth grew from material in its part of space. Moons origin was completely different from Earths. |
From the time it first formed, Earth has always had an atmosphere. | (A) true (B) false | B | An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not stable. |
Some of the gases in Earths early atmosphere came from comets. | (A) true (B) false | A | Earths first atmosphere was different from the current one. The gases came from two sources. Volcanoes spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere (Figure 12.5). Take a look at the list of gases. Whats missing? The early atmosphere had almost no oxygen. |
Our solar system began to form about | (A) 3 billion years ago (B) 4 billion years ago (C) 5 billion years ago (D) 10 billion years ago | C | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. |
When the solar nebula contracted and began to spin, it | (A) increased in temperature (B) increased in pressure (C) formed into a disk (D) all of the above | D | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure |
The inner planets of our solar system include | (A) Pluto (B) Uranus (C) Saturn (D) Mercury | D | The inner planets, or terrestrial planets, are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars. Figure 1.1 shows the relative sizes of these four inner planets. Unlike the outer planets, which have many satellites, Mercury and Venus do not have moons, Earth has one, and Mars has two. Of course, the inner planets have shorter orbits around the Sun, and they all spin more slowly. Geologically, the inner planets are all made of cooled igneous rock with iron cores, and all have been geologically active, at least early in their history. None of the inner planets has rings. Click image to the left or use the URL below. URL: This composite shows the relative sizes of the four inner planets. From left to right, they are Mercury, Venus, Earth, and Mars. |
After the sun formed, material at similar distances from the sun collided to form each of the | (A) moons (B) planets (C) asteroids (D) comets | B | Material at a similar distances from the Sun collided together to form each of the planets. Earth grew from material in its part of space. Moons origin was completely different from Earths. |
Earth formed about | (A) 45 billion years ago (B) 3 billion years ago (C) 1 billion years ago (D) 05 billion years ago | A | Earth came together (accreted) from the cloud of dust and gas known as the solar nebula nearly 4.6 billion years ago, the same time the Sun and the rest of the solar system formed. Gravity caused small bodies of rock and metal orbiting the proto-Sun to smash together to create larger bodies. Over time, the planetoids got larger and larger until they became planets. |
Gases in Earths early atmosphere included | (A) oxygen (B) water vapor (C) carbon dioxide (D) all of the above | D | Earths first atmosphere was made of hydrogen and helium, the gases that were common in this region of the solar system as it was forming. Most of these gases were drawn into the center of the solar nebula to form the Sun. When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. High heat in Earths early days meant that there were constant volcanic eruptions, which released gases from the mantle into the atmosphere (see opening image). Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions. Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system (Figure Calculations also show that asteroids and comets cannot be responsible for all of the gases of the early atmosphere, so both impacts and outgassing were needed. |
After the oceans formed on Earths surface, the | (A) water cycle began (B) atmosphere formed (C) mantle started to cool (D) all of the above | A | When Earth first formed, it was a fiery hot, barren ball. It had no oceans or atmosphere. Rivers of melted rock flowed over its surface. Gradually, the planet cooled and formed a solid crust. Gases from volcanoes formed an atmosphere, although it contained only a trace of oxygen. As the planet continued to cool, clouds formed and rain fell. Rainwater helped form oceans. The ancient atmosphere and oceans would be toxic to modern life, but they set the stage for life to begin. |
The fourth supercontinent to form was | (A) Pangaea (B) Rodinia (C) Escherichia (D) none of the above | B | There are times in Earth history when all of the continents came together to form a supercontinent. Supercontinents come together and then break apart. Pangaea was the last supercontinent on Earth, but it was not the first. The supercontinent before Pangaea is called Rodinia. Rodinia contained about 75% of the continental landmass that is present today. The supercontinent came together about 1.1 billion years ago. Rodinia was not the first supercontinent either. Scientists think that three supercontinents came before Rodina, making five so far in Earth history. |
Earths first crust was probably made of | (A) anorthosite (B) granite (C) basalt (D) peridotite | B | The first crust was made of basaltic rock, like the current ocean crust. Partial melting of the lower portion of the basaltic crust began more than 4 billion years ago. This created the silica-rich crust that became the felsic continents. |
The supercontinent in question 1 formed about | (A) 50 billion years ago (B) 45 billion years ago (C) 40 billion years ago (D) 11 billion years ago | D | By the end of the Archean, about 2.5 billion years ago, plate tectonics processes were completely recognizable. Small Proterozoic continents known as microcontinents collided to create supercontinents, which resulted in the uplift of massive mountain ranges. The history of the North American craton is an example of what generally happened to the cratons during the Precambrian. As the craton drifted, it collided with microcontinents and oceanic island arcs, which were added to the continents. Convergence was especially active between 1.5 and 1.0 billion years ago. These lands came together to create the continent of Laurentia. About 1.1 billion years ago, Laurentia became part of the supercontinent Rodinia (Figure 1.1). Rodinia probably contained all of the landmass at the time, which was about 75% of the continental landmass present today. Rodinia broke up about 750 million years ago. The geological evidence for this breakup includes large lava flows that are found where continental rifting took place. Seafloor spreading eventually started and created the oceans between the continents. The breakup of Rodinia may have triggered Snowball Earth around 700 million years ago. |
The earliest life on Earth | (A) may have been wiped out more than once (B) got its nutrients from photosynthesis (C) passed genetic information using amino acids (D) all of these | A | For the first 4 billion years of Earth history there is only a little evidence of life. Organisms were tiny and soft and did not fossilize well. But scientists use a variety of ways to figure out what this early life was like. |
Early Earth had | (A) many volcanoes (B) high temperatures (C) abundant earthquakes (D) all of the above | D | When Earth formed 4.6 billion years ago, it would not have been called the water planet. There were no oceans then. In fact, there was no liquid water at all. Early Earth was too hot for liquid water to exist. Earths early years were spent as molten rock and metal. |
How do cells make copies of themselves? | (A) Nucleic acids pass on genetic information (B) Using their metabolism (C) By combining cells to become multi-cellular (D) None of these | A | Prokaryotes reproduce asexually. This can happen by binary fission or budding. In binary fission, a cell splits in two. First, the large circular chromosome is copied. Then the cell divides to form two new daughter cells. Each has a copy of the parent cells chromosome. In budding, a new cell grows from a bud on the parent cell. It only breaks off to form a new cell when it is fully formed. |
Which of the following is true? | (A) Prokaryotes and eukaryotes are both only single celled (B) Prokaryotes are only single-celled; eukaryotes are only multicellular (C) Prokaryotes are single-celled or multicellular; eukaryotes are only multicellular (D) Prokaryotes and eukaryotes both are single-celled or multicellular | D | The following is an analysis of the statements above: 1. This is a fact made from observation. 2. The first part is from observations. The second is a fact drawn from the prior observations. The third is an opinion, since she might actually have allergies or the flu. Tests could be done to see what is causing her illness. 3. This is a fact. Many, many scientific experiments have shown that colds are caused by viruses. 4. While that sounds like a fact, the scientific evidence is mixed. One reputable study published in 2007 showed a decrease of 58%, but several other studies have shown no beneficial effect. 5. Bill Gates is the wealthiest man in the United States; thats a fact. But theres no evidence that hes also the smartest man, and chances are hes not. This is an opinion. 6. This sounds like a fact, but it is not. It is easy to test. Gather together a large number of subjects, each with a friend. Have the friends fill out a questionnaire describing the subject. Match the traits against the persons astrological sign to see if the astrological predictions fit. Are Leos actually more fiery, self assured, and charming? Tests like this have not supported the claims of astrologers, yet astrologers have not modified their opinions. 7. This is a fact. The Figure 1.2 shows the temperature anomaly since 1880. Theres no doubt that temperature has risen overall since 1880 and especially since the late 1970s. Global Average Annual Temperatures are Rising. This graph shows temperature anomaly relative to the 1951-1980 aver- age (the average is made to be 0). The green bars show uncertainty. |
Earths earliest life forms | (A) consisted of one cell (B) could breathe oxygen (C) lacked a cell membrane (D) none of the above | A | There is good evidence that life has probably existed on Earth for most of Earths history. Fossils of blue-green algae found in Australia are the oldest fossils of life forms on Earth. They are at least 3.5 billion years old ( Figure 1.1). |
The earliest organisms to photosynthesize | (A) first appeared about a billion years ago (B) went extinct millions of years ago (C) are still common in lakes and seas (D) two of the above | C | The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years and are still alive today (Figure 12.7). Now they are called blue-green algae. They are common in lakes and seas and account for 20% to 30% of photosynthesis today. |
Continents form when | (A) seafloor spreading creates them (B) Earth melts and then re-solidifies (C) microcontinents or island arcs collide (D) none of these | C | Continents grow when microcontinents, or small continents, collide with each other or with a larger continent. Oceanic island arcs also collide with continents to make them grow. |
Eukaryotes first evolved about | (A) 45 billion years ago (B) 35 billion years ago (C) 20 billion years ago (D) 05 billion years ago | C | Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes, eukaryotes have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. Eukaryotes were better able to live and so became the dominant life form. |
Which of the following types of organisms evolved first? | (A) multicellular organisms (B) Ediacara fauna (C) cyanobacteria (D) eukaryotes | C | Bacteria are the most successful organisms on the planet. They lived on this planet for two billion years before the first eukaryotes and, during that time, evolved into millions of different species. |
Prokaryoes are more common than eukaryotes. | (A) true (B) false | B | Most prokaryotic cells are much smaller than eukaryotic cells. Prokaryotic cells are typically only 0.2-2.0 microm- eter in diameter. Eukaryotic cells are about 50 times as big. Prokaryotic cells have a variety of different cell shapes. Figure 8.3 shows three of the most common shapes: spirals (helices), spheres, and rods. Bacteria may be classified by their shape. |
DNA is short for deoxyribonucleic acid | (A) true (B) false | A | DNA is the material that makes up our chromosomes and stores our genetic information. When you build a house, you need a blueprint, a set of instructions that tells you how to build. The DNA is like the blueprint for living organisms. The genetic information is a set of instructions that tell your cells what to do. DNA is an abbreviation for deoxyribonucleic acid. As you may recall, nucleic acids are a type of macromolecule that store information. The deoxyribo part of the name refers to the name of the sugar that is contained in DNA, deoxyribose. DNA may provide the instructions to make up all living things, but it is actually a very simple molecule. DNA is made of a very long chain of nucleotides. In fact, in you, the smallest DNA molecule has well over 20 million nucleotides. |
Rodinia was the first supercontinent. | (A) true (B) false | B | There are times in Earth history when all of the continents came together to form a supercontinent. Supercontinents come together and then break apart. Pangaea was the last supercontinent on Earth, but it was not the first. The supercontinent before Pangaea is called Rodinia. Rodinia contained about 75% of the continental landmass that is present today. The supercontinent came together about 1.1 billion years ago. Rodinia was not the first supercontinent either. Scientists think that three supercontinents came before Rodina, making five so far in Earth history. |
Early in Earth history mantle convection was super fast. | (A) true (B) false | A | Since the early Earth was very hot, mantle convection was very rapid. Plate tectonics likely moved very quickly. The early Earth was a very active place with abundant volcanic eruptions and earthquakes. The remnants of these early rocks are now seen in the ancient cores of the continents. |
The evolution from prokaryotes to eukaryotes to multi-cellular organisms took a few million years. | (A) true (B) false | B | For life to evolve from simple single-celled organisms to many millions of species of prokaryotic species to simple eukaryotic species to all the protists, fungi, plants, and animals, took some time. Well over 3 billion years. |
Nucleic acids in living things include DNA and RNA. | (A) true (B) false | A | Nucleic acids are biochemical molecules that contain oxygen, nitrogen, and phosphorus in addition to carbon and hydrogen. There are two main types of nucleic acids. They are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). |
Continental crust first appeared on Earth about 2 billion years ago. | (A) true (B) false | B | The earliest crust was probably basalt. It may have resembled the current seafloor. This crust formed before there were any oceans. More than 4 billion years ago, continental crust appeared. The first continents were very small compared with those today. |
The first continents on Earth were very large compared with those today. | (A) true (B) false | B | The earliest crust was probably basalt. It may have resembled the current seafloor. This crust formed before there were any oceans. More than 4 billion years ago, continental crust appeared. The first continents were very small compared with those today. |
Pangaea was the first supercontinent to form on Earth. | (A) true (B) false | B | Pangaea was the last supercontinent on Earth. Evidence for the existence of Pangaea was what Alfred Wegener used to create his continental drift hypothesis, which was described in the chapter Plate Tectonics. As the continents move and the land masses change shape, the shape of the oceans changes too. During the time of Pangaea, about 250 million years ago, most of Earths water was collected in a huge ocean called Panthalassa (Figure 1.2). Click image to the left or use the URL below. URL: |
Life may have originated on Earth more than once. | (A) true (B) false | A | No one knows how or when life first began on the turbulent early Earth. There is little hard evidence from so long ago. Scientists think that it is extremely likely that life began and was wiped out more than once; for example, by the impact that created the Moon. This issue of whats living and whats not becomes important when talking about the origin of life. If were going to know when a blob of organic material crossed over into being alive, we need to have a definition of life. |
The first oxygen on Earth combined with iron to form iron oxide. | (A) true (B) false | A | What evidence do scientists have that large quantities of oxygen entered the atmosphere? The iron contained in the rocks combined with the oxygen to form reddish iron oxides. By the beginning of the Proterozoic, banded-iron formations (BIFs) were forming. Banded-iron formations display alternating bands of iron oxide and iron-poor chert that probably represent a seasonal cycle of an aerobic and an anaerobic environment. The oldest BIFs are 3.7 billion years old, but they are very common during the Great Oxygenation Event 2.4 billion years ago (Figure 1.2). By 1.8 billion years ago, the amount of BIF declined. In recent times, the iron in these formations has been mined, and that explains the location of the auto industry in the upper Midwest. |
Some of the oxygen in Earths early atmosphere became ozone. | (A) true (B) false | A | The second atmosphere, which was the first to stay with the planet, formed from volcanic outgassing and comet ices. This atmosphere had lots of water vapor, carbon dioxide, nitrogen, and methane but almost no oxygen. Why was there so little oxygen? Plants produce oxygen when they photosynthesize but life had not yet begun or had not yet developed photosynthesis. In the early atmosphere, oxygen only appeared when sunlight split water molecules into hydrogen and oxygen and the oxygen accumulated in the atmosphere. Without oxygen, life was restricted to tiny simple organisms. Why is oxygen essential for most life on Earth? 1. Oxygen is needed to make ozone, a molecule made of three oxygen ions, O3 . Ozone collects in the atmospheric ozone layer and blocks harmful ultraviolet radiation from the Sun. Without an ozone layer, life in the early Earth was almost impossible. 2. Animals need oxygen to breathe. No animals would have been able to breathe in Earths early atmosphere. |
The first photosynthetic organisms were most like modern E. coli. | (A) true (B) false | B | The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years and are still alive today (Figure 12.7). Now they are called blue-green algae. They are common in lakes and seas and account for 20% to 30% of photosynthesis today. |
There are no longer any prokaryotes living on Earth. | (A) true (B) false | B | Prokaryotes were the first living things to evolve on Earth, probably around 3.8 billion years ago. They were the only living things until the first eukaryotic cells evolved about 2 billion years ago. Prokaryotes are still the most numerous organisms on Earth. Its not certain how the three domains of life are related. Archaea were once thought to be offshoots of Bacteria that were adapted to extreme environments. For their part, Bacteria were considered to be ancestors of Eukarya. Scientists now know that Archaea share several traits with Eukarya that Bacteria do not share. How can this be explained? One hypothesis is that the first Eukarya formed when an archaean cell fused with a bacterial cell. By fusing, the two prokaryotic cells became the nucleus and cytoplasm of a new eukaryotic cell. If this hypothesis is correct, both prokaryotic domains are ancestors of Eukarya. |
Ediacara fauna evolved toward the end of the Precambrian Era. | (A) true (B) false | A | For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular. Toward the end of the Precambrian, the Ediacara Fauna evolved (Figure 12.8). These are the fossils discovered by Walcott in the introduction to the next section. The Ediacara was extremely diverse. They appeared after Earth defrosted from a worldwide glaciation. The Ediacara fauna seem to have died out. Other multicellular organisms appeared in the Phanerozoic. |
first organisms to make food by photosynthesis | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | E | The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years and are still alive today (Figure 12.7). Now they are called blue-green algae. They are common in lakes and seas and account for 20% to 30% of photosynthesis today. |
type of organism that contains a nucleus in its cell(s) | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | C | Eukaryotic cells contain a nucleus and several other types of organelles. These structures carry out many vital cell functions. |
process that added oxygen to Earths early atmosphere | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | G | When photosynthesis evolved and spread around the planet, oxygen was released in abundance. The addition of oxygen is what created Earths third atmosphere. This event, which occurred about 2.5 billion years ago, is sometimes called the oxygen catastrophe because so many organisms died. Although entire species died out and went extinct, this event is also called the Great Oxygenation Event because it was a great opportunity. The organisms that survived developed a use for oxygen through cellular respiration, the process by which cells can obtain energy from organic molecules. This opened up many opportunities for organisms to evolve to fill different niches and many new types of organisms first appeared on Earth. |
gas that protects Earth from harmful radiation | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | F | Gases in the atmosphere surround Earth like a blanket. They keep the temperature in a range that can support life. The gases keep out some of the Suns scorching heat during the day. At night, they hold the heat close to the surface, so it doesnt radiate out into space. |
type of organism that lacks a nucleus in its cell(s) | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | D | Prokaryotic cells are cells that lack a nucleus. The DNA in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane. All the organisms in the Bacteria and Archaea Domains have prokaryotic cells. No other organisms have this type of cell. Organisms with prokaryotic cells are called prokaryotes. They are all single-celled organisms. They were the first type of organisms to evolve. They are still the most numerous organisms today. You can see a model of a prokaryotic cell in Figure 3.3. The cell in the figure is a bacterium. Notice how it contains a cell membrane, cytoplasm, ribosomes, and several other structures. However, the cell lacks a nucleus. The cells DNA is circular. It coils up in a mass called a nucleoid that floats in the cytoplasm. |
organic compound that stores genetic information | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | A | Living cells need organic molecules, known as nucleic acids, to store genetic information and pass it to the next generation. Deoxyribonucleic acid (DNA) is the nucleic acid that carries information for nearly all living cells today and did for most of Earths history. Ribonucleic acid (RNA) delivers genetic instructions to the location in a cell where protein is synthesized. |
waste product of photosynthesis | (A) nucleic acid (B) oxygen (C) eukaryote (D) prokaryote (E) cyanobacteria (F) ozone (G) photosynthesis | B | What is produced by the plant cell during photosynthesis? The products of photosynthesis are glucose and oxygen. This means they are produced at the end of photosynthesis. Glucose, the food of plants, can be used to store energy in the form of large carbohydrate molecules. Glucose is a simple sugar molecule which can be combined with other glucose molecules to form large carbohydrates, such as starch. Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata. As you know, animals need oxygen to live. Without photosynthetic organisms like plants, there would not be enough oxygen in the atmosphere for animals to survive. |
About what percent of Earths surface is covered with water? | (A) 20 percent (B) 50 percent (C) 70 percent (D) 90 percent | C | Oceans cover more than 70 percent of Earths surface and hold 97 percent of its surface water. Its no surprise that the oceans have a big influence on the planet. The oceans affect the atmosphere, climate, and living things. |
Water is stored in | (A) ice and snow (B) the atmosphere (C) lakes and streams (D) all of these | D | Most of Earths water is stored in the oceans, where it can remain for hundreds or thousands of years. |
What percent of Earths total water is fresh water? | (A) 3 percent (B) 52 percent (C) 79 percent (D) 97 percent | A | One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). |
The largest amount of fresh water is contained in | (A) ice caps (B) glaciers and inland seas (C) b rivers and streams (D) c the oceans (E) d groundwater and soil moisture | A | Earths oceans contain 97% of the planets water. That leaves just 3% as fresh water, water with low concentrations of salts (Figure 1.1). Most fresh water is trapped as ice in the vast glaciers and ice sheets of Greenland and Antarctica. How is the 3% of fresh water divided into different reservoirs? How much of that water is useful for living creatures? How much for people? A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time. The distribution of Earths water. Click image to the left or use the URL below. URL: |
Most of Earths liquid fresh water is located in | (A) underground rocks (B) living organisms (C) surface soil (D) large lakes | A | One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). |
The water cycle | (A) begins and ends in the oceans (B) has no beginning and has no end (C) begins in the oceans and ends in groundwater aquifers (D) begins in the atmosphere and ends in the oceans | B | Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle. |
The energy for the water cycle comes from | (A) radioactive decay (B) Earths internal heat (C) the Sun (D) water when it changes state | C | The Sun, many millions of kilometers away, provides the energy that drives the water cycle. Our nearest star directly impacts the water cycle by supplying the energy needed for evaporation. |
Most fresh water enters the atmosphere when water evaporates from | (A) oceans (B) plants (C) lakes (D) soils | A | Water changes from a liquid to a gas by evaporation to become water vapor. The Suns energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a fresh water reservoir. The water vapor remains in the atmosphere until it undergoes condensation to become tiny droplets of liquid. The droplets gather in clouds, which are blown about the globe by wind. As the water droplets in the clouds collide and grow, they fall from the sky as precipitation. Precipitation can be rain, sleet, hail, or snow. Sometimes precipitation falls back into the ocean and sometimes it falls onto the land surface. |
Clouds form when water vapor | (A) evaporates (B) condenses (C) transpires (D) freezes | B | Clouds form when water vapor condenses around particles in the air. The particles are specks of matter, such as dust or smoke. Billions of these tiny water droplets come together to make up a cloud. If the air is very cold, ice crystals form instead of liquid water. |
In infiltration, water goes | (A) through the ground (B) to the atmosphere by changing from liquid to gas (C) to the atmosphere through a plant (D) none of these | A | Some water soaks into the ground. It travels down through tiny holes in soil. It seeps through cracks in rock. The water moves slowly, pulled deeper and deeper by gravity. Underground water can also erode and deposit material. |
Forms of precipitation include | (A) rain (B) snow (C) sleet (D) all of the above | D | The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets (Figure 1.2). They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. One million cloud droplets will combine to make only one rain drop! If temperatures are cold, the droplet will hit the ground as snow. (a) Dew on a flower. (b) Hoar frost. (a) Rain falls from clouds when the temperature is fairly warm. (b) Snow storm in Helsinki, Finland. Other less common types of precipitation are sleet (Figure 1.3). Sleet is rain that becomes ice as it hits a layer of freezing air near the ground. If a frigid raindrop freezes on the frigid ground, it forms glaze. Hail forms in cumulonimbus clouds with strong updrafts. An ice particle travels until it finally becomes too heavy and it drops. (a) Sleet. (b) Glaze. (c) Hail. This large hail stone is about 6 cm (2.5 inches) in diameter. Click image to the left or use the URL below. URL: |
Water vapor enters the atmosphere through | (A) infiltration (B) transpiration (C) condensation (D) two of the above | B | Figure 15.2 shows the role of the atmosphere in the water cycle. Water vapor rises from Earths surface into the atmosphere. As it rises, it cools. The water vapor may then condense into water droplets and form clouds. If enough water droplets collect in clouds they may fall as rain. This how freshwater gets from the atmosphere back to Earths surface. |
Icebergs are made of frozen salt water. | (A) true (B) false | B | You dont have to be an ice climber to enjoy ice. Skating and fishing are two other sports that are also done on ice. What is ice? Its simply water in the solid state. The process in which water or any other liquid changes to a solid is called freezing. Freezing occurs when a liquid cools to a point at which its particles no longer have enough energy to overcome the force of attraction between them. Instead, the particles remain in fixed positions, crowded closely together, as shown in the Figure 1.1. |
Almost 80 percent of Earths fresh water is frozen. | (A) true (B) false | A | One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). |
There is more water in Earths living things than there is in the atmosphere. | (A) true (B) false | B | Oceans cover more than 70 percent of Earths surface and hold 97 percent of its surface water. Its no surprise that the oceans have a big influence on the planet. The oceans affect the atmosphere, climate, and living things. |
Soil moisture is important for plants to grow. | (A) true (B) false | A | A significant amount of water infiltrates into the ground. Soil moisture is an important reservoir for water (Figure The moisture content of soil in the United States varies greatly. |
Some water molecules may be billions of years old. | (A) true (B) false | A | Did you ever wonder where the water in your glass came from or where its been? The next time you take a drink of water, think about this. Each water molecule has probably been around for billions of years. Thats because Earths water is constantly recycled. |
Water exists on Earth in all three states of matter. | (A) true (B) false | A | Water is the only substance on Earth that is present in all three states of matter - as a solid, liquid or gas. (And Earth is the only planet where water is abundantly present in all three states.) Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure 1.2). (a) Ice floating in the sea. Can you find all three phases of water in this image? (b) Liquid water. (c) Water vapor is invisible, but clouds that form when water vapor condenses are not. Click image to the left or use the URL below. URL: |
The water cycle has no beginning or end. | (A) true (B) false | A | Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle. |
Water can go through the water cycle without changing state. | (A) true (B) false | B | Water keeps changing state as it goes through the water cycle. This means that it can be a solid, liquid, or gas. How does water change state? How does it keep moving through the cycle? As Figure 13.3 shows, several processes are involved. Evaporation changes liquid water to water vapor. Energy from the Sun causes water to evaporate. Most evaporation is from the oceans because they cover so much area. The water vapor rises into the atmosphere. Transpiration is like evaporation because it changes liquid water to water vapor. In transpiration, plants release water vapor through their leaves. This water vapor rises into the atmosphere. Condensation changes water vapor to liquid water. As air rises higher into the atmosphere, it cools. Cool air can hold less water vapor than warm air. So some of the water vapor condenses into water droplets. Water droplets may form clouds. Precipitation is water that falls from clouds to Earths surface. Water droplets in clouds fall to Earth when they become too large to stay aloft. The water falls as rain if the air is warm. If the air is cold, the water may freeze and fall as snow, sleet, or hail. Most precipitation falls into the oceans. Some falls on land. Runoff is precipitation that flows over the surface of the land. This water may travel to a river, lake, or ocean. Runoff may pick up fertilizer and other pollutants and deliver them to the water body where it ends up. In this way, runoff may pollute bodies of water. Infiltration is the process by which water soaks into the ground. Some of the water may seep deep under- ground. Some may stay in the soil, where plants can absorb it with their roots. In all these ways, water keeps cycling. The water cycle repeats over and over again. Who knows? Maybe a water molecule that you drink today once quenched the thirst of a dinosaur. |
Water turns to gas through condensation. | (A) true (B) false | B | Water changes to a gas by three different processes called evaporation, sublimation, and transpiration. Evaporation takes place when water on Earths surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration takes place when plants release water vapor through pores in their leaves called stomata. |
Most condensation of water takes place in the oceans. | (A) true (B) false | B | The oceans are an essential part of Earths water cycle. Since they cover so much of the planet, most evaporation comes from oceans and most precipitation falls on oceans. |
The atoms that make up water molecules come together and break apart easily. | (A) true (B) false | B | Water is an amazing molecule. It has a very simple chemical formula, H2 O. It is made of just two hydrogen atoms bonded to one oxygen atom. Water is remarkable in terms of all the things it can do. Lots of things dissolve easily in water. Some types of rock can even completely dissolve in water! Other minerals change by adding water into their structure. |
Cold air can hold less water than warm air so when air cools water may condense. | (A) true (B) false | A | When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. |
Water that forms clouds always falls to the ground as precipitation. | (A) true (B) false | B | Clouds are needed for precipitation. This may fall as liquid water, or it may fall as frozen water, such as snow. |
Runoff may pollute rivers, lakes, and oceans. | (A) true (B) false | A | Runoff from crops, livestock, and poultry farming carries contaminants such as fertilizers, pesticides, and animal waste into nearby waterways (Figure 1.3). Soil and silt also run off farms. Animal wastes may carry harmful diseases, particularly in the developing world. The high density of animals in a factory farm means that runoff from the area is full of pollutants. Fertilizers that run off of lawns and farm fields are extremely harmful to the environment. Nutrients, such as nitrates, in the fertilizer promote algae growth in the water they flow into. With the excess nutrients, lakes, rivers, and bays become clogged with algae and aquatic plants. Eventually these organisms die and decompose. Decomposition uses up all the dissolved oxygen in the water. Without oxygen, large numbers of plants, fish, and bottom-dwelling animals die. |
Most of Earths precipitation falls on land. | (A) true (B) false | B | Most precipitation that occurs over land, however, is not absorbed by the soil and is called runoff. This runoff collects in streams and rivers and eventually flows back into the ocean. |
water that falls from clouds to Earths surface | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | F | Water changes from a liquid to a gas by evaporation to become water vapor. The Suns energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a fresh water reservoir. The water vapor remains in the atmosphere until it undergoes condensation to become tiny droplets of liquid. The droplets gather in clouds, which are blown about the globe by wind. As the water droplets in the clouds collide and grow, they fall from the sky as precipitation. Precipitation can be rain, sleet, hail, or snow. Sometimes precipitation falls back into the ocean and sometimes it falls onto the land surface. |
continuous movement of water through the oceans, atmosphere, land, and living things | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | D | Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle. |
process in which plants release water vapor through their leaves | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | E | Plants and animals depend on water to live. They also play a role in the water cycle. Plants take up water from the soil and release large amounts of water vapor into the air through their leaves (Figure 1.3), a process known as transpiration. |
precipitation that flows over the surface of the ground | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | G | Most precipitation that occurs over land, however, is not absorbed by the soil and is called runoff. This runoff collects in streams and rivers and eventually flows back into the ocean. |
process in which water vapor changes to liquid water | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | A | Water changes to a gas by three different processes called evaporation, sublimation, and transpiration. Evaporation takes place when water on Earths surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration takes place when plants release water vapor through pores in their leaves called stomata. |
process in which liquid water changes to water vapor | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | B | Water changes to a gas by three different processes called evaporation, sublimation, and transpiration. Evaporation takes place when water on Earths surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration takes place when plants release water vapor through pores in their leaves called stomata. |
process in which water soaks into the ground | (A) condensation (B) evaporation (C) infiltration (D) water cycle (E) transpiration (F) precipitation (G) runoff | C | Some water soaks into the ground. It travels down through tiny holes in soil. It seeps through cracks in rock. The water moves slowly, pulled deeper and deeper by gravity. Underground water can also erode and deposit material. |
Possible sources of water in a lake include | (A) rivers (B) runoff (C) precipitation (D) all of the above | D | Ponds and lakes may get their water from several sources. Some falls directly into them as precipitation. Some enters as runoff and some from streams and rivers. Water leaves ponds and lakes through evaporation and also as outflow. |
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