Astronomy

Where is solid material found in the layers of Earth's structure? A. mantle and core B. crust only C. crust and inner core D. crust and outer core E. continents only

C. crust and inner core

Label the interior layers of a terrestrial planet. Hint: The Earth is a terrestrial planet. What does its interior look like?

Inside: Core; Middle: Mantle; Outside: Crust

Rank these conditions by the final temperature of Earth (highest to lowest)

1. 500 ppm CO2 & 2600 ppb CH4; 2. 500 ppm CO2 & 1 ppb CH4; 3. 250 ppm CO2 & 2600 ppb CH4; 4. 250 ppm CO2 & 1 ppb CH4; 5. 1 ppm CO2 & 2600 ppb CH4; 6. 1 ppm CO2 & 1 ppb CH4

Order the stages of planetary formation from first to last. Hint: Think about the interior structure and surface of a terrestrial planet. What would have shaped it first? What stages occur as direct effects of previous stages?

1. Differentiation; 2. Cooling; 3. Cratering; 4. Magma Flooding; 5. Weathering

The particles in an atmosphere will not escape the gravitational pull of a celestial body if their velocity is smaller than 1/6 the escape velocity of the celestial body. The escape velocity is dependent on the mass (M) and radius (R) of the celestial body. The Interactive allows you to select from multiple celestial bodies to see how the escape velocity changes. Rank the celestial bodies on how likely they would be able to retain a gas at high temperature (likely to least likely)

1. Jupiter; 2. Venus; 3. Mercury; 4. Moon; 5. Ceres

Find the stable temperature of an airless world with an albedo of 0.10 orbiting 7.40 × 10^11 meters from a star with a radius of 2.00 × 10^9 meters and a surface temperature of 6400.00 K.

229.15K

Using the information from the Interactive, select the most appropriate answer below. A. As the luminosity of the star increases, the equilibrium temperature of the planet increases. B. As the luminosity of the star decreases, the equilibrium temperature of the planet increases. C. As the luminosity of the star increases, the equilibrium temperature of the planet does not change. D. As the luminosity of the star increases, the equilibrium temperature of the planet decreases.

A. As the luminosity of the star increases, the equilibrium temperature of the planet increases.

A surge in a crowd is an example of what kind of wave? A. P-wave B. both S- and P-waves C. It is not a wave at all. D. neither S- nor P-wave E. S-wave

A. P-wave

Which of the following would you expect to differ significantly between a long-period comet and an asteroid? A. distance between the point of origin and the Sun B. albedo at perihelion C. radius D. inclination of orbit E. distance at aphelion

A. distance between the point of origin and the Sun B. albedo at perihelion D. inclination of orbit E. distance at aphelion

What makes a typical Earth-crossing asteroid difficult to detect and track? A. its albedo B. its density C. the low eccentricity of its orbit D. its lack of an atmosphere E. its low velocity relative to background stars

A. its albedo

When volcanoes erupt, the spewed material comes from which layer of Earth? A. ocean floor B. mantle C. molten core D. solid core E. crust

B. mantle

What determines the path of the ion tail of a comet? A. Earth's gravity B. the direction of the solar wind C. the Sun's gravity D. the conservation of angular momentum E. the solar magnetic cycle

B. the direction of the solar wind

Why are strong winter storms not an argument against global warming? A. Global warming will increase sea ice melting which puts more salt water near coastlines and increases winter storm strength. B. Winter storms are driven by dust in the atmosphere and oceans, and global warming means a dusty upper atmosphere. So winter storms will become more severe. C. All storms are driven by energy in the atmosphere and oceans, and global warming means more energy held by the atmosphere. So storms of all types — including winter storms — can become more severe. D. Winter storms are not getting stronger anywhere on the planet on average. E. Global warming will increase volcanic eruptions which darkens the sky increases winter storm strength.

C. All storms are driven by energy in the atmosphere and oceans, and global warming means more energy held by the atmosphere. So storms of all types — including winter storms — can become more severe.

If Deimos were orbiting at its current orbital radius around Earth instead of around Mars, how would its orbital velocity differ? A. It would be the same. B. It would be faster because of Earth's greater radius. C. It would be faster because of Earth's greater mass. D. It would be slower because of Earth's greater radius. E. It would be slower because of Earth's greater mass.

C. It would be faster because of Earth's greater mass

Four planets that formed at the same time have equal density and the following radii: planet W: 2,000 km planet X: 2,500 km planet Y: 2,700 km planet Z: 5,000 km Ignoring any other factors, which planet would be expected to cool fastest? A. planet Y, with radius 2,700 km B. planet X, with radius 2,500 km C. Planet W, with radius 2,000 km D. planet Z, with radius 5,000 km E. There is no way to know.

C. Planet W, with radius 2,000 km

What is the defining characteristic of the Trojan asteroids? A. They are rocky. B. They are the remnants of an inner terrestrial planet. C. They orbit ahead of and behind Jupiter. D. They are the largest known asteroids. E. They orbit within Saturn's rings.

C. They orbit ahead of and behind Jupiter.

This image shows the relative sizes of the terrestrial planets and their order from the Sun (closest toward the left, farthest toward the right). Assume that, based on crater counts, the geological age of the planetary surfaces from oldest to youngest is Mercury, Mars, Venus, Earth. Based on the information above, which of the following properties of a planet is most important in determining its level of recent geological activity? A. distance from the Sun B. amount of water on the surface C. size D. rotation rate E. albedo (percentage of sunlight that is reflected from the surface)

C. size

Sort each description as describing a comet or an asteroid

Comet: composed of ice and rock, form tails when near the Sun, found mostly in the Oort Cloud Asteroid: composed mainly of rock, mostly found between Mars and Jupiter

Comparing the orbital inclination of Pluto to those of other planets, what conclusion can we draw? A. It is higher, implying that Pluto likely was captured from deep space. B. It is lower, implying that Pluto likely has never had gravitational interactions. C. It is lower, implying that Pluto was likely formed by a different mechanism than other Solar System bodies. D. It is higher, implying that Pluto likely underwent gravitational interactions with other planets. E. None of the answer options are correct.

D. It is higher, implying that Pluto likely underwent gravitational interactions with other planets.

Use the Interactive to investigate which of the following statements are true. Choose one or more: A. Mercury has no atmosphere. B. The Earth and Mars are the same size. C. Earth and Venus have molten iron surrounding the core. D. The Earth and Mercury are the only two terrestrial planets with a magnetic field. E. All terrestrial planets have a crust.

D. The Earth and Mercury are the only two terrestrial planets with a magnetic field E. All terrestrial planets have a crust

Which body has the longest "day"? (A day is defined as the interval between the time at which a particular point on the body faces the Sun and the time at which the point faces the Sun again.) A. Earth's Moon B. Mars C. Earth D. Venus E. Mercury

D. Venus

Venus and Earth are similar in size, so they should have had similar amounts of volcanic outgassing adding to the atmosphere, and similar gravities resulting in a similar loss of atmospheric gas to space. Why, then, are their atmospheres so different? This table shows the composition of the planets' atmospheres if all the carbon dioxide that exists anywhere on the planet were included: Carbon dioxide is added to the atmosphere through volcanic outgassing, and it is removed as it is absorbed by liquid water and then chemically combined with rock. Based on the text above and what you see in the table, what is the most likely reason Venus has a stronger greenhouse effect than Earth? A. Venus is covered in clouds that reflect most of the sunlight away. B. Venus has a higher percentage of nitrogen than the Earth. C. Venus had more carbon dioxide added to the air through volcanic outgassing. D. Venus is closer to the Sun, so any liquid water that might have existed on the surface in the distant past would have evaporated away faster than on the Earth.

D. Venus is closer to the Sun, so any liquid water that might have existed on the surface in the distant past would have evaporated away faster than on the Earth.

Which two planets are the closest in rotational period? A. Mercury and Earth B. Mars and Mercury C. Mars and Venus D. Venus and Earth E. Earth and Mars

E. Earth and Mars

Which of the following statements about the atmosphere of Venus is not true? A. It is mostly CO2. B. It contains sulfuric acid clouds. C. Its heat and acidity quickly disable spacecraft that land on the surface. D. Its composition has changed significantly over time. E. It is 90 times less dense than Earth's atmosphere.

E. It is 90 times less dense than Earth's atmosphere.

Which of the following does not describe an effect that the Moon has on Earth? A. creating the tides B. decreasing Earth's rotational speed C. limiting the wobble in Earth's spin D. lengthening Earth's day E. stabilizing Earth's climate

E. stabilizing Earth's climate

A caldera is which of the following? A. a channel dug by the glancing blow of an asteroid B. a crest formed by the meeting of two crustal plates C. a long ridge formed by planet shrinkage D. a depression that filled with lava E. the depression at the top of a volcano

E. the depression at the top of a volcano

Sort the following descriptions by whether they pertain to Mercury, the Moon, or both. Hint: Mercury is much denser than our rocky Moon. What does that suggest about its interior?

Mercury: Very large iron core Moon: Surface has maria caused by past collisions and volcanic activity Both: Inhospitable to biological life; Highly cratered surface; Very little atmosphere

Sort these statements about the greenhouse effect by whether they are true, false, or if it is unclear based on just information within the Interactive. You may need to draw simple conclusions from the information provided by the Interactive.

True: CO2 has a stronger impact on the final temperature than CH4 within the ranges of the Interactive; Increasing CO2 increases the final temperature. False: Decreasing CH4 increases the final temperature; An Earth with no CO2 or CH4 would have a final temperature of 0 K. Unclear: CO2 and CH4 are the only greenhouse gases that affect Earth's temperature.

Which of the following statements about Earth's magnetic field are true? Sort as true or false.

True: It is caused by electric currents in Earth's molten iron core; It traps solar wind particles, causing auroras; Its north and south magnetic poles occasionally reverse. False: It is the dominant magnetic field in the Solar System; It keeps the Moon in orbit around Earth.

The four planets closest to the Sun have similar compositions (rock/metal), and all have solid surfaces. They are therefore grouped together as terrestrial ("Earth-like") planets. Even though they formed from the same process of accretion in the Solar Nebula, you'll see here that their surfaces are significantly different from one another. Why are these planets so different? To answer this, we must start with an understanding of the processes that cause planetary surfaces to change: volcanism, tectonics, erosion, and impacts.

Volcanism/Tectonics: Rising mantle material Erosion: Wind, ice Impacts: Meteorites

Calculate the thermal velocity of an atom in the atmosphere of a planet with a temperature of 260.00 K if the atom is 7.00 times more massive than hydrogen.

0.975 km/s

The radius of an exoplanet is 2.00 times larger than Earth's radius. What is the ratio of Earth's cooling time to the exoplanet's cooling time?

0.5

A planet's temperature depends on its distance from the Sun as well as the strength of its greenhouse effect. Let's remove the effect of distance from the Sun by just considering how the temperature of a planet changes due to the presence of its atmosphere. From the numbers given in the animation, calculate the difference in temperature for each planet with and without its atmosphere, and then rank the planets in order of increasing greenhouse effect.

1. Mars; 2. Earth; 3. Venus

Using the information from the Interactive, rank the following terrestrial planets from highest to lowest in equilibrium temperature.

1. Mercury; 2. Earth; 3. Mars; 4. Jupiter

Rank the terrestrial planets from longest rotational period to shortest rotational period. Hint: "Rotational period" is also known as the length of a day on a planet.

1. Venus; 2. Mercury; 3. Mars; 4. Earth

The radius of planet APC-11 is r, while the radius of planet APC-23 is 2.2r. How do their cooling times compare? Hint: The cooling time is proportional to the ratio of the volume (proportional to r3) divided by the surface area (proportional to r2). A. APC-11 will take about half as long to cool as APC-23 B. Both will take the same time to cool C. APC-11 will take about twice as long to cool as APC-23 D. APC-11 will cool about 4 times as fast E. The question can't be answered without knowing the volume of both planets

A. APC-11 will take about half as long to cool as APC-23

Skeptics point out that the climate has varied naturally in the past, and we are still here. Which argument refutes this claim? A. People have always changed the climate and it has gone through temperature changes greater than 4 degrees Celsius many times in the last 10,000 years. B. Ice ages are a hoax by scientists to get more vacation time. C. The ice ages were caused by volcanos whereas modern warming is occurring due to erosion of rocks via concrete construction. D. Over the period of the ice ages there was no climate change so whatever is happening now must be natural. E. Over the period of the ice ages the climate changed over centuries at least which was very slow. In contrast, the changes we are causing today are happening over decades.

A. People have always changed the climate and it has gone through temperature changes greater than 4 degrees Celsius many times in the last 10,000 years.

Comparing objects in our Solar System can give us important clues toward understanding their properties that we wouldn't obtain through just studying each object independently. Comparing Earth's Moon to those of the other planets may also help us understand more about it. Examine this table and choose the statements below it that match your observations. A. The Earth's moon is unique in that it is much larger than the moons of the other inner planets. B. The Earth's moon is unique in that it is less dense than the moons of the other inner planets. C. The Earth's moon is typical in all ways when compared to the moons of the other inner planets. D. Only half of the inner planets have moons.

A. The Earth's moon is unique in that it is much larger than the moons of the other inner planets. D. Only half of the inner planets have moons.

Weather is quite different from climate. Weather describes short-term variations in temperature in a localized place on Earth, while climate refers to the overall average temperature in a large region over a long period of time. To get an accurate indication of where Earth's temperature is heading in the long term, we must look back over a long period of time at the average behavior of the climate as a whole, ignoring short-term changes in weather. With this in mind, study the plot below. A. The climate is getting warmer with time. B. The climate is getting colder with time. C. The climate is changing completely at random, with no noticeable general trend.

A. The climate is getting warmer with time

Detailed observations of a long-period comet, near aphelion, would most likely not include which of the following? A. coma B. nucleus C. ion tail D. jets E. dust tail

A. coma C. ion tail D. jets E. dust tail

Which is these statements is one of the 3 facts in the Climate Primar's Climate 1-2-3? A. The average time for the ocean to absorb CO2 is much longer than the time to emit methane leading to oscillations in the time over which ice ages and greenhouse warming occur. B. Human activity, especially the use of fossil fuels — by which we mean coal, oil, and gas, all of which release carbon dioxide when burned — is adding significantly more of this heat-trapping gas to Earth's atmosphere. C. Sunspots have been increasing leading to an increase in the temperature of the Sun which, in turn, leads to more UV radiation hitting the upper atmosphere and increasing the strength of cooling at high altitude. D. Earth did not have water early in its history and that has impacted it's ability to retain heat now. E. Water vapor is a greenhouse gas, by which we mean a gas that emits heat and makes a planet warmer than it would be otherwise.

B. Human activity, especially the use of fossil fuels — by which we mean coal, oil, and gas, all of which release carbon dioxide when burned — is adding significantly more of this heat-trapping gas to Earth's atmosphere.

If we experience a year that is much hotter than the previous year, this means that Earth is going through a global warming trend, where the temperature will now continually increase each year. A. false B. It is impossible to tell with one year of data. C. true

B. It is impossible to tell with one year of data.

Sort these conditions by whether the final temperature is higher or lower than 278 K.

Below 278 K: 250 ppm CO2 & 1 ppb CH4; 1 ppm CO2 & 2600 ppb CH4; 0 ppm CO2 & 0 ppb CH4 Above 278 K: 500 ppm CO2 & 2600 ppb CH4

A half-life is defined as the amount of time it takes for half of one isotope, called the parent isotope, to decay to another isotope, called the daughter isotope. The Interactive allows you to select a variety of isotopes to see their different decay times, what their daughter isotopes will be, and how long, in relative timescales, the decay process will take. Select any isotope and press the play button to start the Interactive. A. The daughter isotope is more stable than the parent isotope, so the process is less chaotic. B. The initial half-life brings the total parent isotope from 100% to 50%. The next half-life drops the total parent isotope from 50% to 25%. The next half-life drops the total parent isotope from 25% to 12.5%. The total amount of original parent isotope being converted to daughter isotope is decreasing with each half-life. Therefore, the entire process takes longer, but the half-life is not changing. C. The half-life decreases with time because there is less parent isotope with time. D. Half-life is a random process that will speed up and slow down erratically.

B. The initial half-life brings the total parent isotope from 100% to 50%. The next half-life drops the total parent isotope from 50% to 25%. The next half-life drops the total parent isotope from 25% to 12.5%. The total amount of original parent isotope being converted to daughter isotope is decreasing with each half-life. Therefore, the entire process takes longer, but the half-life is not changing.

Generally speaking, as you increase your distance from a star, you greatly decrease your equilibrium temperature. Let's apply this to our own Solar System. Using your basic understanding of the Solar System or the interactive, which planet has the highest equilibrium temperature?

Mercury

The Interactive also shows you the direction of the rotation of each terrestrial planet. The Earth has a prograde rotation, which means it rotates in a counterclockwise direction when viewed top-down from its North Pole. Using the Interactive, sort the remaining planets Mercury, Venus, and Mars as having either a prograde or retrograde rotation. Hint: Look at how the Earth rotates. Which other planets rotate in the same direction?

Prograde: Mars; Mercury Retrograde: Venus

Sort the following statements by whether they are considered evidence for plate tectonics or not.

Tectonic Evidence: matching fossils in different landmasses, the shapes of the continents, observed motion of the continents, convection in the mantle Not Evidence: locations of deserts, distribution of hurricanes, ice caps on the North and South Poles

Rank these CO2 conditions by the final temperature of Earth (highest to lowest)

1. 500 ppm CO2; 2. 400 ppm CO2; 3. 300 ppm CO2; 4. 200 ppm CO2; 5. 100 ppm CO2; 6. 0 ppm CO2

Rank the terrestrial planets in order of their cooling rates from fastest to slowest. Hint: The rate of cooling is inversely proportional to the radius of a planet. (Inversely proportional means as one quantity gets bigger, the other gets smaller in response.)

1. Mercury; 2. Mars; 3. Venus; 4. Earth

A half-life is defined as the amount of time it takes for half of one isotope, called the parent isotope, to decay to another isotope, called the daughter isotope. Compare their relative half-lives and rank the isotopes from the longest half-life to the shortest half-life.

1. U > Pb; 2. K > Ar; 3. Fe > Ni; 4. Al > Mg

Rank the following layers by their depth from the surface of the Earth.

1. crust; 2. mantle; 3. outer core; 4. inner core

Rank the layers of Earth's atmosphere from the highest layer to the lowest layer.

1. ionosphere; 2. mesosphere; 3. stratosphere; 4. troposphere

Assume that a rock sample initially contained 6000.00 U-238 nuclei 6.00 billion years ago. How many lead-206 nuclei would it contain today?

3618.90 nuclei

A half-life is defined as the amount of time it takes for half of one isotope, called the parent isotope, to decay to another isotope, called the daughter isotope. We know that after 1 half-life, 50% of the parent isotope remains, and after 2 half-lives, 25% of the parent isotope remains. Following this logic, it would take _______ half-lives to reach 3.125% of the parent isotope remaining.

5

A half-life is defined as the amount of time it takes for half of one isotope, called the parent isotope, to decay to another isotope, called the daughter isotope. Let's try to understand what is happening on a molecular level. Let's assume your object, initially, is made up entirely of the parent isotope you selected. If the parent isotope goes through 1 half-life, then the total amount of parent isotope remaining is 50%. What percentage of the daughter isotope makes up the object now?

50%

A half-life is defined as the amount of time it takes for half of one isotope, called the parent isotope, to decay to another isotope, called the daughter isotope. We know that after 1 half-life, 50% of the parent isotope remains, and after 2 half-lives, 25% of the parent isotope remains. Following this logic, _____ of the parent isotope would remain after 4 half-lives.

6.25%

What is the orbital velocity, in kilometers per second, of a planet with 6.00 times the orbital radius of Mars? Hint: The orbital velocity of Mars is 24.1 km/s.

9.83 km/s

Which is these statements is one of the 3 facts in the Climate Primar's Climate 1-2-3? A. Carbon dioxide is a greenhouse gas, by which we mean a gas that traps heat and makes a planet (like Earth or Venus) warmer than it would be otherwise. B. The Sun's energy output has annual cycles that have been increasing over the last 1,000,000 million years and this explains why CO2 output of oceans is larger than expected and leads to the climate change we see now. C. Sunspots have been increasing leading to an increase in the temperature of the Sun which, in turn, leads to more UV radiation hitting the upper atmosphere and increasing the strength of cooling at high altitude. D. Earth did not have water early in its history and that has impacted it's ability to retain heat now. E. The average time for the ocean to absorb CO2 is much longer than the time to emit methane leading to oscillations in the time over which ice ages and greenhouse warming occur.

A. Carbon dioxide is a greenhouse gas, by which we mean a gas that traps heat and makes a planet (like Earth or Venus) warmer than it would be otherwise.

In the seafloor map below, the arrows show the motion of the ocean plates. Where is new crust being made? Choose all that apply. A. Australian-Pacific plate boundary B. Australian-Antarctic plate boundary C. Pacific-Nazca plate boundary D. Pacific-Scotia plate boundary

B. Australian-Antarctic plate boundary C. Pacific-Nazca plate boundary D. Pacific-Scotia plate boundary

Which of the following is not a source of heat in the interiors of the terrestrial planets? Hint: Which of the sources affects primarily the interior of the planets? A. Radioactive decay B. Friction between atmosphere and surface C. Gravitational compression D. Collisions from other bodies E. Differentiation

B. Friction between atmosphere and surface

The greenhouse effect plays a major role in the climate of a planet. Visit the Greenhouse Effect AstroTour, and use what you learn there to choose all the statements below that are correct. Note that 273 K = 0°C = 32°F. A. It would be beneficial to humanity to develop technology that would eliminate the greenhouse effect on Earth. B. If there were no greenhouse effect, liquid water would not exist on the surface of the Earth. C. The more carbon dioxide there is in an atmosphere, the stronger the greenhouse effect will be. D. The Earth absorbs sunlight and reemits it in the ultraviolet. E. The Earth has reached thermal equilibrium, emitting the same amount of energy into space as it absorbs from the Sun.

B. If there were no greenhouse effect, liquid water would not exist on the surface of the Earth. C. The more carbon dioxide there is in an atmosphere, the stronger the greenhouse effect will be. E. The Earth has reached thermal equilibrium, emitting the same amount of energy into space as it absorbs from the Sun.

Earth is special among the planets because it has an ozone layer to protect it from ultraviolet light that can destroy water vapor molecules and a strong magnetic field to protect it from the solar wind stripping off its atmosphere. It has just the right air pressure, and it is at just the right distance from the Sun for liquid water to exist on its surface. Because carbon dioxide is removed from the atmosphere by liquid water, this is key in keeping Earth's atmospheric carbon dioxide level in check. The upper graph shows the carbon dioxide content in Earth's atmosphere as a function of time, and the lower graph shows the average yearly temperature in Antarctica, where the carbon dioxide levels were measured. Note that the units of time are in thousands of years. Study the above figure, then select all the statements below that are correct. A. There is no correlation between the carbon dioxide content in the atmosphere and temperature. B. There are cyclical temperature variations seen on this graph (a periodic increase, then decrease) every few 10,000 to 100,000 years or so. C. The temperature is inversely related to the amount of carbon dioxide in the atmosphere—a decrease in one results in an increase in the other. D. There are cyclical temperature variations seen on this graph (a periodic increase, then decrease) each year due to the passage of the seasons. E. The temperature is directly related to the amount of carbon dioxide in the atmosphere—an increase in one coincides with an increase in the other.

B. There are cyclical temperature variations seen on this graph (a periodic increase, then decrease) every few 10,000 to 100,000 years or so. E. The temperature is directly related to the amount of carbon dioxide in the atmosphere—an increase in one coincides with an increase in the other.

Compare the atmospheric properties of the planets in the table to the right. The surface temperature is the average for the entire planet in units of Kelvin (subtract 273 from that number to convert it into units of Celsius). The surface pressure is related to how thick the atmosphere is (thicker atmospheres have more air molecules packed into the same volume, and thus higher pressure). Given the information in this table, how would you explain the difference in greenhouse effect strength for each of the planets? A. Earth has a much higher percentage of nitrogen in its atmosphere, causing it to have a stronger greenhouse effect than Venus and Mars. B. Venus has a very strong greenhouse effect because it has a high percentage of carbon dioxide in its atmosphere and also a high surface pressure. C. Venus and Mars both have a very high percentage of carbon dioxide in their atmospheres, creating a stronger greenhouse effect than Earth's atmosphere, which has very little. D. Mars has a weak greenhouse effect because it has very low surface pressure. E. Planets that are closer to the Sun will have a stronger greenhouse effect than those farther away from the Sun.

B. Venus has a very strong greenhouse effect because it has a high percentage of carbon dioxide in its atmosphere and also a high surface pressure. D. Mars has a weak greenhouse effect because it has very low surface pressure.

According to the data, the global average temperature of the Earth is increasing. Based on the two plots below, what is likely causing this? A. a gradual increase in the strength of the greenhouse effect over the past 2,000 years B. a gradual decrease in the strength of the greenhouse effect over the past 2,000 years C. a sudden increase in the strength of the greenhouse effect over the past 100-200 years D. a sudden decrease in the strength of the greenhouse effect over the past 100-200 years

C. a sudden increase in the strength of the greenhouse effect over the past 100-200 years