Suppose that you were an extraterrestrial being visiting Earth for the first time. What would you see? How would you interpret your observations? Imagine yourself in the role of the explorer/reporter assigned the task of visiting Earth and writing a report about the planet for a magazine article back home. This chapter is written from the point of view of an imaginary explorer/reporter from the fictitious planet called Epsilon Eridani 2.
Until now in this course, measurement units such as kilometers, miles, and degrees usually have been written out in full. However, starting with this chapter, I will use more abbreviated symbology. This is the way scientists usually write such expressions, so you should get used to it too.
This chapter is written as a fictitious story, but all the scientific information is based on well-documented knowledge. While the explorers from Epsilon Eridani 2 are make-believe characters, the things they see are real, although viewed from perspectives we don’t normally consider. It has been said that it is difficult to see a big picture when you are inside the frame. Let’s step outside the frame for awhile. Here is the log of the first officer of the fictitious Epsilon Eridanian exploration vessel, the Dragon.
As our ship approaches the planet Sol 3, the third planet in orbit around the star that we call Sol, we are struck by the amazing blue and white colors. Previous probes have shown us that the white regions are clouds of water vapor and ice ranging in altitude from zero (at the surface) up to about 16 kilometers (km) or 10 miles (mi). The surface is well-defined, and more than half of it is liquid water. Some of the surface is frozen water; other regions show an amazing variety of features, the details of which it is part of this mission to catalogue.
We settle into a circular, polar orbit at an altitude of 500 km (300 mi). From this vantage point, over time we will be able to map in detail the entire surface of the planet using radar and optical equipment. We all look forward to the landings. We will go down two-by-two, and because there are 20 of us and we each are to be allowed only one trip, we will make 10 different landings in 10 different places on the surface.
There are regions on Sol 3 where plant life abounds, sometimes only a millimeter (less than 1/16 inch) tall and in other places upwards of 100 m (330 ft) in height. Plants also live in and around bodies of water. The largest water zones are tainted with sodium chloride (salt) and other minerals. At low latitudes, but never exactly at the equator, revolving storms occasionally occur; from our initial orbit we count five of these. The largest has a diameter of more than 1000 km (600 mi). Animal life also has been observed both on the solid surface and beneath the liquid surface. These animals exist in a range of sizes similar to those of the plants.
The most interesting structures on the planet will require extensive investigation. Their geometry suggests life forms having great intelligence some of the time and amazing stupidity at other times.
Some of these structures appear as monoliths in great congregations, perforated by holes covered over with glass. Narrow, solid strips serve as pathways for objects resembling gigantic rolling insects that go from place to place in an orderly fashion but without apparent overall purpose. Two-legged life forms have been seen entering and exiting these rolling insects. Apparently the insects are not life forms themselves but rather are vehicles designed by the life forms that enter and leave them and are intended to transport those life forms from place to place within and between the great congregations of monoliths, which, for lack of any other name at this point, I will henceforth call anthills.
I can hardly wait to land right in the middle of one of these anthills and see what happens close-up. I have already picked the one I want to check out. It is located at approximately 41°N and 73°W. According to electromagnetic signals from this anthill, it calls itself New York. There is an open, green area in the middle of this congregation of monoliths that appears ideal for a landing.
Other large insect-like vehicles have been seen flying through the air at altitudes approaching those of the highest icy clouds. When these flying vehicles are on the ground, the two-legged life forms have been seen entering and leaving them in large groups. Apparently these vehicles are designed for the purpose of transporting the life forms between anthills separated by great distances. The two-legged life forms also have been seen entering and leaving objects that slowly float on and across bodies of water, avoiding, of course, the revolving storms but nevertheless sometimes enduring wave action that would challenge the stomachs of our hardiest space travelers. Sometimes it seems as if these two-legged life forms use their vehicles for the sole purpose of having a violent ride!
The equatorial plane of Sol 3, which the two-legged inhabitants call Earth, is tilted by approximately 23.5 degrees with respect to the plane of its orbit around the parent star Sol, which they call the Sun. This results in considerable seasonal variations in the weather that become increasingly dramatic as the latitude increases. The hours of daylight and darkness are always equal at the equator, but fluctuations become greater and greater as one goes nearer to the poles. North of 66.5°N and south of 66.5°S, there are periods when the Sun stays above the horizon for days at a stretch. At the poles themselves, the daylight period lasts for fully half the year, and the darkness period lasts for the other half.
There are about 365.25 solar days in each Earth year. It is difficult for me to describe the length of the Earth day except to say that the two-legged creatures divide each day into 24 equal units called hours. Each hour is divided into 60 minutes, and each minute is divided into 60 seconds. Fractions of a second are expressed in decimal form. For some reason, most Earth inhabitants divide the solar day into two 12-hour segments called A.M. and P.M. Some of their scientists use an undivided hour system that runs from 0000 (zero hours, zero minutes) to 2359 (23 hours and 59 minutes) and then starts over again at 0000 in the middle of the dark period.
The Earth is farthest from the Sun (that is, it is at aphelion) in the month called July and is closest to the Sun (that is, at perihelion) in the month called January. The mean distance of the Earth from the Sun is 149.6 million km (93 million mi). The variation in orbital radius is only about ±1 percent. The Earth’s greater distance from the Sun in the northern-hemispheric summer results in less solar irradiation over the planet’s greatest land masses at that time. However, this effect is balanced by the fact that the season is lengthened; Earth moves more slowly around the Sun at that time (Fig. 8-1). Conversely, the Earth’s lesser distance from the Sun during the northern-hemispheric winter produces more solar irradiation, but the season is shorter because the Earth moves faster around the Sun.
The earth’s axis precesses, or wobbles, slowly like the axis of a spinning top. Every 25,800 Earth years, the axis describes a complete circle whose angular radius is 23.5 angular degrees on the celestial sphere. This means that in 12,900 years, Earth will be closest to the Sun in July and farthest from the Sun in January (Fig. 8-2). It is difficult to say what effect this might have on the overall climate of the planet. There is much more land mass in the northern hemisphere than in the southern; land masses heat up and cool off more rapidly than the oceans. This could have a tremendous cumulative effect when the northern-hemispheric summer is shortened and the winter is lengthened. It is known that the repeated cycles of glaciation that take place on our own planet, Epsilon Eridani 2 (the second planet in orbit around the star Earth inhabitants call Epsilon in the constellation Eridanus), also have taken place on Earth; axial precession might be a contributing factor to these so-called ice ages.
Figure 8-1. Earth is at perihelion in January and at aphelion in July. (In this drawing, the eccentricity of Earth’s orbit is exaggerated for clarity.)
Figure 8-2. In 12,900 years, Earth will be at perihelion in July and at aphelion in January. (In this drawing, the eccentricity of Earth’s orbit is exaggerated for clarity.)
The Earth has a slightly larger diameter at the equator than at the poles. This oblateness, or flattening, is caused by the rotation of the planet. The effect is too small to be visually apparent as the planet is seen from space; the outer planets, especially Jupiter and Saturn, are much more oblate than is the Earth and actually look that way. The Earth’s diameter is 12,756 km (7,926 mi) in the plane of the equator and 12,714 km (7,900 mi) as measured along the rotational axis from pole to pole.
Time is one of the most powerful forces in the Cosmos. The Earth-dwelling two-legged creatures who call themselves Homo sapiens have not developed a mature concept of this power and how it can be harnessed. If they had a better understanding of time and how things happen in the long term—millions upon millions of their years—many of the mysteries that befuddle them would become clear and simple in their minds.
Suppose it were possible to look at time so that a year seemed to pass in a fraction of a second? How would Earth look when beheld from such a perspective? The precession of the axis would be apparent; Earth would look like a furiously spinning top. The continents would drift around like ice floes on an Arctic lake during the springtime thaw. In some places large chunks of land would break away from continents. In other places islands would bump into continents and join up with them. Crumpling of the crust, caused by the drifting of land masses, would create mountain ranges. The Hawaiian Islands would drift toward the northwest, eroding down into the ocean at the northwestern end and being born anew in continuous volcanic eruptions at the southeastern end. The sea level would rise and fall periodically; glaciers would advance and retreat. The Earth, which seems like a stable place on a day-to-day scale, would be revealed as dynamic, fluid orb. One might be tempted to suppose that Earth has a life of its own, that it is a gigantic biological cell. An idea of this sort has been posed by some respected Earth scientists. It is called the Gaia hypothesis. However, this notion has not been proven true, and many academics have dismissed it as unscientific.
Given sufficient time, rivers cut canyons hundreds of meters deep. One of the best-known examples is the Grand Canyon in the southwestern United States. It is hard to imagine, on an hour-by-hour or day-by-day scale, how the little Colorado River could have gouged out such a ravine, but time is patient beyond all human understanding. Time has unlimited endurance. It works day and night; it never rests. It carves and chips and grinds, builds new structures atom by atom or cell by cell, and keeps on doing its work for human lifetime after human lifetime, generation after generation, age after age. Time has been at work on Earth for more than 4 billion human-defined years and will continue to mold and change the planet for at least that many years yet to come.
The Earth can be considered to have four distinct layers. The central portion, called the inner core, is believed to be solid. It is extremely hot and consists mainly of iron and nickel. These metals are ferromagnetic, meaning that they can be magnetized. Surrounding the inner core is a liquid iron and nickel layer called the outer core. This liquid flows in huge eddies that are thought to be responsible for the magnetization of the core and hence for the existence of the geomagnetic field.
Above the outer core lies the mantle, consisting of rock similar to granite (called basaltic rock). The consistency of the mantle would appear solid if you could take a piece of it and hold it in your hand. However, on a long time scale and considered in its entirety, it is a fluid mass. As the eons pass, the mantle flows much like hot tar or molasses, rising up from the center of the planet toward the surface in some places and descending in other zones. One theory holds that this is a mechanism for the transfer of heat from the hot core regions to the surface, where the heat energy ultimately is transferred to the atmosphere and radiated into space. The up-and-down currents result in lateral movement near the upper reaches of the mantle.
The outermost layer, called the crust, floats on top of the mantle and, as the ages pass, moves around on it. The lateral movements of the mantle carry chunks of crust along. The crust is not a uniform, continuous mass but instead has regions where it is deep (about 30 km, or 20 mi) and other regions where it is shallow (perhaps as thin as 10 km, or 6 mi). The thickest parts of the crust form the continents and larger islands. The thin regions lie beneath the seas and oceans. Figure 8-3 is a simplified cross-sectional diagram of the Earth as it would appear if it were sliced in half at the equator.
Figure 8-3. Simplified cross-sectional diagram of Earth.
The surface of Earth is largely covered by mineral-rich oceans of water. The largest of these, if seen from a certain vantage point in space, covers almost half the planet. This is the Pacific Ocean; it was given this name by some Earth dweller who saw it at one of its more peaceful moments. (Pacific means “peaceful” or “tranquil.”) However, this ocean is not always calm. Revolving storms, called hurricanes in the eastern Pacific and typhoons in the western Pacific, churn the waters and transport excess heat from the tropics toward the polar regions.
Hurricanes also occur in the Atlantic Ocean and in the Indian Ocean. The storms form at lower latitudes, and they almost always work their way either onto a land mass, where they dissipate, or toward cold water, where they expire from lack of heat to sustain their winds. Occasionally, one of these storms strikes a human-made anthill. Some of the planet’s most elaborate anthills are built directly in known hurricane tracks. I wonder why the human Earth dwellers construct so many of their communities in such places?
The waters flow in slow currents around and around the oceanic basins, generally clockwise in the northern hemisphere and counterclockwise in the southern. This gives rise to warm ocean currents along the eastern shores of the continents and cold currents along the western shores. This has a profound influence on the distribution and movement of weather systems in the planet’s atmosphere. When something happens to upset the regularity of these currents, the climate changes over much of the planet. These cycles are natural and have been taking place for millions of human-defined years. However, almost every time such a cycle recurs, especially the sort known as El Niño where the eastern equatorial Pacific waters switch from cold to warm, the humans call the resulting weather a disaster.
The oceans are critical to the balance of life on Earth. They are like the lungs and blood of a living organism. Tiny life forms called plankton live in the oceans; these are eaten by larger life forms such as the fish. Fish are a favored food among the two-legged humans. However, humans dump toxic chemicals and hydrocarbon dregs into the oceans, where they work their way into fish and then into their brothers’ and sisters’ bodies, causing terrible illnesses and suffering. Humans know about this. We have heard them talk about it in their electromagnetic broadcasts. Why do they continue to knowingly harm themselves in this way?
The oceans tend to heat up and cool down slowly. They hold heat energy. Land masses are just the opposite. They heat up and cool down rapidly. This contrast, along with the oceanic currents and the prevailing differences in temperature between the tropics and the polar regions, creates the climate and weather variations on this third planet from the star we call Sol. Earth is the only planet with weather varied enough to motivate the evolution of life but not so violent or hostile as to exterminate such life before it gets a chance to evolve.
In some places water accumulates in the atmosphere and then precipitates onto land masses in great amounts. This can happen either as liquid water, in which case it is called rain, or as frozen water, known as snow. There are other, less common forms of precipitation, such as hail, but these do not contribute much to the overall ecological system of the Earth.
In the regions where precipitation is abundant and mostly liquid, forests of tall plants grow. Some of these plants are cut down and used as materials by the two-legged humans in the construction of dwellings in their anthills. It is amazing how many different geometries have been invented for these dwellings! The plants, called trees, make ideal building material, and they can be replenished by intelligent management. Unfortunately, in some regions of the planet no attempts are made to replenish the supply of trees. Humans obviously know the supply of trees is not infinite and eventually will be depleted if balance is not maintained. Do they not care about their own future?
The Earth’s atmosphere is 78 percent nitrogen at the surface and 21 percent oxygen. The remaining 1 percent consists of argon, carbon dioxide, ozone, and water vapor. The temperature of the atmosphere varies considerably; it can rise to about 55°C (130°F), or plunge to around –80°C (–112°F).
The lowest layer of the atmosphere, rising from the surface to approximately 16 km (10 mi) of altitude, is the troposphere. This is where all weather occurs; most of the clouds are found here. In the upper parts of the troposphere, high-speed rivers of air travel around the planet in a generally west-to-east direction. There can be two or three of these rivers in the northern hemisphere and two or three in the southern hemisphere. The strongest of these rivers, called jet streams, carry high- and low-pressure systems from west to east at temperate latitudes, primarily between 30°N and 60°N, and between 30°S and 60°S.
Above the troposphere lies the stratosphere, extending up to approximately 50 km (30 mi) of altitude. Near the upper reaches of this level, ultraviolet radiation from the Sun causes oxygen atoms to group together into triplets (O3) rather than in pairs (O2), as is the case nearer the surface. An oxygen triplet is a molecule known as ozone. This gas has the unique property of being opaque to ultraviolet rays. Thus oxygen atoms form a self-regulating mechanism that keeps the Earth’s surface from receiving too much ultraviolet from the Sun. Certain gases are produced by industrial processes carried on by the two-legged humans; these gases rise into the stratosphere and cause the ozone molecules to break apart into their individual atoms. This makes the upper stratosphere more transparent to ultraviolet than it would be if nature had its way. Some humans have demonstrated that if this process continues, it could have an adverse effect on all life on the planet. Other humans do not believe this and continue to produce these potentially dangerous industrial by-products.
Above the stratosphere lies the mesosphere, extending from 50 km (30 mi) to an altitude of 80 km (50 mi). In this layer, ultraviolet radiation from the Sun causes electrons to be stripped away from atoms of atmospheric gas. The result is that the mesosphere contains a large proportion of ions. This occurs in a layer that communications engineers call the D layer of the ionosphere.
Above the mesosphere lies the highest layer of the Earth’s atmosphere, known as the thermosphere. It extends from 80 km (50 mi) up to more than 600 km (370 mi) of altitude. This layer gets its name from the fact that the temperature is extremely high, even hotter than at the surface of Venus or Mercury. However, these high temperatures do not have the devastating effects they would have if they existed at the surface because the atmosphere at this level is so rarefied. Ionization takes place at three levels within the thermosphere, called the ionospheric E layer, F1 layer, and F2 layer. Sometimes, particularly at night, the F1 and F2 layers merge together near the altitude of the F2 layer; the resulting layer is called the F layer. Figure 8-4 is a diagram of the Earth’s atmosphere showing the various layers and the ionized regions.
Figure 8-4. The Earth’s atmosphere, showing the ionized layers.
I have just received a stern warning from the authorities back home on Epsilon Eridani 2. Their mandates are as follows:
Our Earth landing assignments have been reduced from 10 to 3.
We are not to land within 50 km (30 mi) of any place known to be populated, even sparsely, with the two-legged life forms that call themselves Homo sapiens.
We are to keep our radar and optical cloaking devices activated at all times.
If we accidentally happen to encounter any Homo sapiens, we are to explain to them that we are part of a “Hollywood movie set” and then ask them to leave.
This seems to defeat the most important part of our mission: to find out exactly what makes Homo sapiens behave as they do. However, I can’t fight the bureaucracy of Epsilon Eridani 2! I will have to be content with looking at these creatures, whom I have decided to call bipedal ants, through telescopes while in orbit and analyzing their migration patterns with radar and computer programs.
We descend into the middle of the Azores-Bermuda high-pressure system in the North Atlantic Ocean, hoping to find calm conditions. It is the part of the Earth year that the bipedal ants call April, when hurricanes are unknown in this part of the planet. Nevertheless, when we reach the ocean, we find that there are huge waves on the surface. The waves come from the north, and we recall that storms can track across the North Atlantic at any time of the year.
In the northern-hemispheric spring, storms follow the jet stream, coming off the North American continent near the mouth of the St. Lawrence Seaway and taking paths at high latitudes toward Europe. Our meteorology expert on the main ship confirms that one of these storms is passing near Iceland, and it is responsible for generating the waves. We are surprised that waves can travel so far and still be so large, but the main-ship radar telescope indicates that their effects reach all the way south to Antarctica.
The atmosphere is perfectly calm; there is no wind as we land and observe a temperature of 23°C (73°F) at high noon. We float like a cork on the swells, which measure 11 m (36 ft) from crest to trough. The surface of the water is smooth except for these sine-wave-shaped swells, a most remarkable phenomenon.
By sunset, the temperature of the atmosphere has hardly changed; it is 22°C (72°F). At midnight, the atmospheric temperature has gone down to 20°C (68°F), and just before sunrise on the day after our landing, it is at its minimum of 19°C (66°F). This small temperature variation between day and night confirms our theory that the oceans keep the lower atmospheric temperature relatively stable. The water temperature is measured at 20°C (68°F).
We remain on the surface of the ocean, examining the abundant life in the water, for exactly one solar day. We see no signs of the bipedal ants, either on the surface of the ocean or in the atmosphere above it, even though we have been told that aircraft will fly overhead and one of them will descend to investigate us. We are relieved when we lift off at noon, exactly 24 Earth hours after we landed. Because of the violent and continuous motion induced by the waves, I have lost 2.5 kilograms (kg) of body weight. This is 5.5 pounds (lb) in the Earth’s gravitation. It has taken place because I have been unable to eat or drink anything for the past 24 Earth hours without having it come back up. Many bipedal ants suffer this same malady when they are first introduced to oceanic travel; they call it sea-sickness.
Antarctica is a huge ice cap centered at the Earth’s south geographic pole. All the continental land mass, with the exception of a small peninsula that reaches northward toward South America, is covered by water ice throughout the year. This ice extends offshore into the sea for a considerable distance in some places.
It is April, early autumn in the Earth’s southern hemisphere. We are concerned about the possibility of high winds upsetting our craft and low temperatures straining our life-support systems if we land on the ice cap itself. We therefore decide to land at the tip of the Antarctic Peninsula that juts northward. This is not only the northernmost point on the continent, but it is largely surrounded by ocean, which, we hope, would keep temperatures from dropping too low.
As we approach the surface, it becomes apparent that this landing is going to make our North Atlantic excursion seem tame by comparison. We see snow (small flakes of water ice) rushing horizontally along the surface, driven by a wind of hurricane force. When we land, a gust almost knocks our craft off its landing gear and onto its side. Despite this wind, small black-and-white bipedal animals, looking like birds but acting more like bipedal ant children, run around, seemingly unaffected by the tempest. They jump in and out of the water, and some of them waddle up to our vessel and then stand there watching us, as if they expect us to come out and play in the water with them. We reject this option. The temperature is –37°C (–35°F).
The gale increases steadily. We decide to return to the main ship before the storm plucks our landing vessel up and rolls it across the bleak, rocky terrain. It never crosses our minds to venture outside into these conditions, which seem, despite the hospitable atmosphere, more severe than the worst storms we have ever seen on Sol 4 (Mars). Thus we blast off, struggling to maintain stability, and we are relieved when we reach the stratosphere and spot our main ship, the Dragon, as a bright dot in the sky.
The only characteristics that the Sahara Desert shares with Antarctica are wind and dryness. In every other respect the two places are so different that it is hard to believe that they exist on the same planet.
We land at high noon on sandy, rolling terrain that looks like certain parts of Mars but with fewer rocks and boulders. The atmospheric temperature is 49°C (120°F) and rising. There is little wind, but the large dunes give away the fact that strong winds blow regularly in the area. The sky is hazy blue, pinkish near the horizon, again reminiscent of Mars.
By late afternoon, the temperature reaches a peak of 53°C (127°F), which we on Epsilon Eridani 2 consider ideal. The Sun, which has passed the zenith, sets in a ruddy cloud that again reminds us of home. The temperature quickly drops, and a brisk wind comes up. By midnight the temperature is 17°C (63°F), and in the predawn hours it drops to 14°C (57°F). We attribute this large day-night temperature differential to the high altitude of the site we have selected and to the fact that sand does not retain heat very well.
Just before liftoff at sunrise, we see tracks in the sand that appear to have been made by four-legged animals. However, no life is in sight, and we have been strictly warned to avoid the risk of contact with the bipedal ants. According to our Earth sociology books, it is not unknown in the Sahara Desert to see bipedal ants riding four-legged, long-necked animals.
As we blast off, in the distance I see objects moving slowly across the sand. I get my hand telescope and take a magnified look. There is a scene out of a picture book I saw about Earth when I was a child: Four Homo sapiens, each riding a four-legged, long-necked, hump-backed animal! I am astounded. Who would have guessed that the bipedal ants of the planet Earth have progressed to such a level of sophistication that they employ nonmechanized, nonpolluting modes of transportation? I expected, if I saw any life at all in the Sahara, to see them riding crazily around in four-wheeled, internal-combustion-propelled vehicles, tearing up what few plants manage to survive in that environment. Maybe the bipedal ants are not as barbaric as we have supposed.
From what we have seen of Earth, it is a stormy, desolate place. We deliberately chose regions where intelligent life would not likely be found. However, based on these observations, it is hard to imagine how any place on Earth could allow humans to build a civilization without great struggle and sacrifice. The bipedal ants must cooperate closely to build and maintain their anthills. But how can we know what these anthills actually are, what they do, and why they exist until we can visit one of them?
We only looked at three places on Earth, and this is not a sufficient sampling to know the nature of the planet as a whole. Perhaps there are fields of green plants, or undamaged forests, or snowy mountains with small settlements where the bipedal ants can revel in their surroundings and take time to enjoy the art of living. Maybe there are clean lakes and rivers and windy, empty prairies with small individual dwellings separated by enough distance so their occupants do not become mentally and physically deranged. We have heard rumors of such places, and our telescopic observations indicate that they might exist. For now, however, we must content ourselves to visit only desolate regions. We have been told by our security agencies that were these bipedal ants to encounter us, they might think we had come to invade them and react with violence. Even if they did not fear us, they might capture and analyze us, as if we were created by the Cosmos for no other purpose than to arouse and then satisfy their curiosity.
QuizRefer to the text if necessary. A good score is 8 correct. Answers are in the back of the book.
1. The Earth’s atmosphere at the surface consists of
(a) 21 percent oxygen.
(b) 78 percent oxygen.
(c) 1 percent carbon dioxide.
(d) 1 percent ozone.
2. At which of the following latitudes would an observer see the Sun for 24 hours a day during some parts of the year?
(a) 50°N.
(b) 23.5°N.
(d) 75°S.
3. The Earth travels most rapidly in its orbit around the Sun during the month of
(a) January.
(b) April.
(c) July.
(d) October.
4. The Earth’s core is believed to be
(a) extremely cold.
(b) a rarefied gas.
(c) comprised of basaltic rock.
(d) ferromagnetic.
5. The Earth’s axis completes one complete cycle of precession approximately every
(a) 18,000 years.
(b) 12,900 years.
(c) 25,800 years.
(d) 50,000 years.
6. The crust of the Earth is thickest
(a) under continents.
(b) under the oceans.
(c) in the polar regions.
(d) No! The Earth’s crust is uniformly thick everywhere.
7. Because of the generally clockwise flow of waters in the northern-hemispheric oceans
(a) the U.S. West Coast gets a warm equatorial current.
(b) the U.S. East Coast gets a cold polar current.
(c) the coast of China gets a warm equatorial current.
(d) the western coast of southern Africa receives a warm equatorial current.
8. Temperatures over the ocean do not change very much between day and night because
(a) the ocean heats and cools slowly so that it tends to keep the air temperature over it fairly constant between day and night.
(b) land masses radiate heat into the atmosphere at night, where it travels over the oceans and keeps the air there from cooling off.
(c) the salt in the oceans regulates the temperature.
(d) No! Temperatures over the ocean change greatly between day and night.
9. The chemical formula for ozone is
(a) O2.
(b) NO2.
(d) CO2.
10. High- and low-pressure weather systems in the atmosphere are carried from west to east at temperate latitudes by the
(a) oceanic currents.
(b) stratosphere.
(c) ionized layers.
(d) jet streams.
