Global warming is defined as the slow increase in the temperature of the earth’s atmosphere and is caused by pollutants and carbon dioxide (CO₂). While the gradual increase in temperature cannot be refuted, scientists argue over the cause.

 Scientist 1:

Global warming is caused by increases in atmospheric CO₂, which is directly created by humans and their consumption of fossil fuels. The natural CO₂ released from carbon sinks has a different isotopic ratio from the CO₂ released from fossil fuels. Current measurements of the radioactive isotopes of CO₂ show that it is from human activity, not from nature. The Earth’s carbon sinks cannot absorb these large amounts of unnatural CO₂ emissions. About fifty percent of the CO₂ produced by mankind remains in the atmosphere, unable to be absorbed.

Scientist 2:

The rise in atmospheric CO₂ levels are a result of global warming, not the cause of it. When the temperature increases, the CO₂ in carbon sinks is released. While humans do cause release of CO₂, the carbon sinks absorb it. The activity of the carbon sinks increases to allow for higher levels of CO₂ absorption. Proponents for human causation of global warming point to the warming and cooling of the stratosphere, however, these temperature fluctuations are caused by changes in the sun’s heat. These proponents also look at the acidity of the ocean as evidence of human causation, however, the rise in ocean acidity is within the normal range of fluctuations over the past ten thousand years.

Upon what part of the global warming discussion do both Scientist 1 and Scientist 2 agree?

According to the Big Bang theory, which proposes that the universe is roughly 13.7 billion years old, all matter and energy were at one time compressed into a single microscopic point. This point then exploded outward in all directions in a rapid expansion. The expansion has continued to the present day, which has allowed matter to cool to a state at which stable atomic components can form. The Big Bang theory proposes that our universe is finite in age, and since nothing can travel faster than the speed of light, there exists a cosmological horizon, which is the maximum distance light or energy could have travelled since the occurrence of the Big Bang. Since the universe is still expanding, however, regions of space that are visible from our vantage point are not within each other's cosmological horizons. For example, if galaxy A is 10 billion light years away from us, and galaxy B is 10 billion light years away from us in the opposite direction, there is a total distance of 20 billion light years between them. The universe has only existed long enough for light, energy, or information to travel 13.7 billion light years between them; thus, it is not possible for any contact to have been made between the two galaxies. Yet, even these vastly separated regions of space have been observed to be extremely homogeneous—they have remarkably similar features and properties despite being so far away from each other. The question, therefore, is what caused this apparent homogeneity observed in the universe. If matter rapidly expanded outward, why does the universe have such a uniform appearance in every direction? If the Big Bang theory is correct, some explanation for this horizon problem is needed.

Scientist 1

In the current state of the universe there exist regions that lie beyond the cosmological horizons of others, and therefore cannot possibly be influenced by them. This was not always the case. At a point in time mere microseconds after the Big Bang, all of the matter in the universe experienced a period of exponential expansion, known as inflation, before the rate of expansion fell to a more stable level. This inflation led to all regions of the universe having homogeneous features, even though they are not capable of affecting one another in any way in their current state.

Scientist 2

Although there is ample evidence that a Big Bang occurred, the horizon problem, as well as the flatness problem, suggest that the Big Bang is not the full story of the inception of the universe. The horizon problem can be solved if, instead of viewing the Big Bang as the "beginning of everything," we stipulate that the expansion seen after the Big Bang was already occurring for some time before the Big Bang occurred. This marks the Big Bang as a sort of "causal horizon," which disallows us from directly observing evidence from any period beforehand. If we assume the universe is cyclic, the homogeneity of the universe is explained as the result of a continuous cycle of expansion and compression, which would naturally lead to a universe having uniform features.

Assuming that all observed evidence to this point is correct, if a new theory were proposed to explain the origins of the universe, what feature must it be able to explain?

According to the Big Bang theory, which proposes that the universe is roughly 13.7 billion years old, all matter and energy were at one time compressed into a single microscopic point. This point then exploded outward in all directions in a rapid expansion. The expansion has continued to the present day, which has allowed matter to cool to a state at which stable atomic components can form. The Big Bang theory proposes that our universe is finite in age, and since nothing can travel faster than the speed of light, there exists a cosmological horizon, which is the maximum distance light or energy could have travelled since the occurrence of the Big Bang. Since the universe is still expanding, however, regions of space that are visible from our vantage point are not within each other's cosmological horizons. For example, if galaxy A is 10 billion light years away from us, and galaxy B is 10 billion light years away from us in the opposite direction, there is a total distance of 20 billion light years between them. The universe has only existed long enough for light, energy, or information to travel 13.7 billion light years between them; thus, it is not possible for any contact to have been made between the two galaxies. Yet, even these vastly separated regions of space have been observed to be extremely homogeneous—they have remarkably similar features and properties despite being so far away from each other. The question, therefore, is what caused this apparent homogeneity observed in the universe. If matter rapidly expanded outward, why does the universe have such a uniform appearance in every direction? If the Big Bang theory is correct, some explanation for this horizon problem is needed.

Scientist 1

In the current state of the universe there exist regions that lie beyond the cosmological horizons of others, and therefore cannot possibly be influenced by them. This was not always the case. At a point in time mere microseconds after the Big Bang, all of the matter in the universe experienced a period of exponential expansion, known as inflation, before the rate of expansion fell to a more stable level. This inflation led to all regions of the universe having homogeneous features, even though they are not capable of affecting one another in any way in their current state.

Scientist 2

Although there is ample evidence that a Big Bang occurred, the horizon problem, as well as the flatness problem, suggest that the Big Bang is not the full story of the inception of the universe. The horizon problem can be solved if, instead of viewing the Big Bang as the "beginning of everything," we stipulate that the expansion seen after the Big Bang was already occurring for some time before the Big Bang occurred. This marks the Big Bang as a sort of "causal horizon," which disallows us from directly observing evidence from any period beforehand. If we assume the universe is cyclic, the homogeneity of the universe is explained as the result of a continuous cycle of expansion and compression, which would naturally lead to a universe having uniform features.

It can be inferred from Scientist 2's statement that the flatness problem __________.

According to the Big Bang theory, which proposes that the universe is roughly 13.7 billion years old, all matter and energy were at one time compressed into a single microscopic point. This point then exploded outward in all directions in a rapid expansion. The expansion has continued to the present day, which has allowed matter to cool to a state at which stable atomic components can form. The Big Bang theory proposes that our universe is finite in age, and since nothing can travel faster than the speed of light, there exists a cosmological horizon, which is the maximum distance light or energy could have travelled since the occurrence of the Big Bang. Since the universe is still expanding, however, regions of space that are visible from our vantage point are not within each other's cosmological horizons. For example, if galaxy A is 10 billion light years away from us, and galaxy B is 10 billion light years away from us in the opposite direction, there is a total distance of 20 billion light years between them. The universe has only existed long enough for light, energy, or information to travel 13.7 billion light years between them; thus, it is not possible for any contact to have been made between the two galaxies. Yet, even these vastly separated regions of space have been observed to be extremely homogeneous—they have remarkably similar features and properties despite being so far away from each other. The question, therefore, is what caused this apparent homogeneity observed in the universe. If matter rapidly expanded outward, why does the universe have such a uniform appearance in every direction? If the Big Bang theory is correct, some explanation for this horizon problem is needed.

Scientist 1

In the current state of the universe there exist regions that lie beyond the cosmological horizons of others, and therefore cannot possibly be influenced by them. This was not always the case. At a point in time mere microseconds after the Big Bang, all of the matter in the universe experienced a period of exponential expansion, known as inflation, before the rate of expansion fell to a more stable level. This inflation led to all regions of the universe having homogeneous features, even though they are not capable of affecting one another in any way in their current state.

Scientist 2

Although there is ample evidence that a Big Bang occurred, the horizon problem, as well as the flatness problem, suggest that the Big Bang is not the full story of the inception of the universe. The horizon problem can be solved if, instead of viewing the Big Bang as the "beginning of everything," we stipulate that the expansion seen after the Big Bang was already occurring for some time before the Big Bang occurred. This marks the Big Bang as a sort of "causal horizon," which disallows us from directly observing evidence from any period beforehand. If we assume the universe is cyclic, the homogeneity of the universe is explained as the result of a continuous cycle of expansion and compression, which would naturally lead to a universe having uniform features.

From the context of the passage, "light year" most nearly means __________.

According to the Big Bang theory, which proposes that the universe is roughly 13.7 billion years old, all matter and energy were at one time compressed into a single microscopic point. This point then exploded outward in all directions in a rapid expansion. The expansion has continued to the present day, which has allowed matter to cool to a state at which stable atomic components can form. The Big Bang theory proposes that our universe is finite in age, and since nothing can travel faster than the speed of light, there exists a cosmological horizon, which is the maximum distance light or energy could have travelled since the occurrence of the Big Bang. Since the universe is still expanding, however, regions of space that are visible from our vantage point are not within each other's cosmological horizons. For example, if galaxy A is 10 billion light years away from us, and galaxy B is 10 billion light years away from us in the opposite direction, there is a total distance of 20 billion light years between them. The universe has only existed long enough for light, energy, or information to travel 13.7 billion light years between them; thus, it is not possible for any contact to have been made between the two galaxies. Yet, even these vastly separated regions of space have been observed to be extremely homogeneous—they have remarkably similar features and properties despite being so far away from each other. The question, therefore, is what caused this apparent homogeneity observed in the universe. If matter rapidly expanded outward, why does the universe have such a uniform appearance in every direction? If the Big Bang theory is correct, some explanation for this horizon problem is needed.

Scientist 1

In the current state of the universe there exist regions that lie beyond the cosmological horizons of others, and therefore cannot possibly be influenced by them. This was not always the case. At a point in time mere microseconds after the Big Bang, all of the matter in the universe experienced a period of exponential expansion, known as inflation, before the rate of expansion fell to a more stable level. This inflation led to all regions of the universe having homogeneous features, even though they are not capable of affecting one another in any way in their current state.

Scientist 2

Although there is ample evidence that a Big Bang occurred, the horizon problem, as well as the flatness problem, suggest that the Big Bang is not the full story of the inception of the universe. The horizon problem can be solved if, instead of viewing the Big Bang as the "beginning of everything," we stipulate that the expansion seen after the Big Bang was already occurring for some time before the Big Bang occurred. This marks the Big Bang as a sort of "causal horizon," which disallows us from directly observing evidence from any period beforehand. If we assume the universe is cyclic, the homogeneity of the universe is explained as the result of a continuous cycle of expansion and compression, which would naturally lead to a universe having uniform features.

Which of the following, if true, would undermine both scientists' positions?

A rover on Mars tests the soil on the planet in Gale Crater. An instrument on the rover dectects steep spikes in methane levels in the soil within 60 days. Additionally, satellite measurements from the area detect unusual plumes of methane from this specific area, which scientists suggest may have once contained an ancient freshwater lake. Two different scientists discuss whether this evidence is conclusive of the existence of life on the planet. 

Scientist 1

This is the first evidence that organic life exists on Mars. On Earth, 95% of methane gas is produced by microbial organisms, which points towards the presence of similar biological processes on Mars. The rover has also found evidence of water bound to soil in the crater, and pictures showing carvings in the sides of the crater walls suggest the existence of once-flowing water. Because this water could have supported life in the crater, this methane originated from a bacterial source and shows there is life on the planet.

Scientist 2

There is no evidence of life on Mars. These methane spikes came from organic matter left behind from recent meteor impacts as they degraded in the sun's rays. Although the crater was once filled with water, now all water is bound to minerals in the soil and it not accessible. Methane has also been measured on planets such as Saturn, Uranus, and Neptune, which have conditions too hostile to support life. There is not even enough evidence to suggest that the original water in the crater could have supported life. 

Which of the following describes the phenomena to which the scientists attribute methane on Mars?

A rover on Mars tests the soil on the planet in Gale Crater. An instrument on the rover dectects steep spikes in methane levels in the soil within 60 days. Additionally, satellite measurements from the area detect unusual plumes of methane from this specific area, which scientists suggest may have once contained an ancient freshwater lake. Two different scientists discuss whether this evidence is conclusive of the existence of life on the planet. 

Scientist 1

This is the first evidence that organic life exists on Mars. On Earth, 95% of methane gas is produced by microbial organisms, which points towards the presence of similar biological processes on Mars. The rover has also found evidence of water bound to soil in the crater, and pictures showing carvings in the sides of the crater walls suggest the existence of once-flowing water. Because this water could have supported life in the crater, this methane originated from a bacterial source and shows there is life on the planet.

Scientist 2

There is no evidence of life on Mars. These methane spikes came from organic matter left behind from recent meteor impacts as they degraded in the sun's rays. Although the crater was once filled with water, now all water is bound to minerals in the soil and it not accessible. Methane has also been measured on planets such as Saturn, Uranus, and Neptune, which have conditions too hostile to support life. There is not even enough evidence to suggest that the original water in the crater could have supported life. 

According to the information given, upon which of the following points would both scientists agree?

A rover on Mars tests the soil on the planet in Gale Crater. An instrument on the rover dectects steep spikes in methane levels in the soil within 60 days. Additionally, satellite measurements from the area detect unusual plumes of methane from this specific area, which scientists suggest may have once contained an ancient freshwater lake. Two different scientists discuss whether this evidence is conclusive of the existence of life on the planet. 

Scientist 1

This is the first evidence that organic life exists on Mars. On Earth, 95% of methane gas is produced by microbial organisms, which points towards the presence of similar biological processes on Mars. The rover has also found evidence of water bound to soil in the crater, and pictures showing carvings in the sides of the crater walls suggest the existence of once-flowing water. Because this water could have supported life in the crater, this methane originated from a bacterial source and shows there is life on the planet.

Scientist 2

There is no evidence of life on Mars. These methane spikes came from organic matter left behind from recent meteor impacts as they degraded in the sun's rays. Although the crater was once filled with water, now all water is bound to minerals in the soil and it not accessible. Methane has also been measured on planets such as Saturn, Uranus, and Neptune, which have conditions too hostile to support life. There is not even enough evidence to suggest that the original water in the crater could have supported life. 

Which of the conditions in Gale crater would Scientist 1 support but Scientist 2 not support?

A rover on Mars tests the soil on the planet in Gale Crater. An instrument on the rover dectects steep spikes in methane levels in the soil within 60 days. Additionally, satellite measurements from the area detect unusual plumes of methane from this specific area, which scientists suggest may have once contained an ancient freshwater lake. Two different scientists discuss whether this evidence is conclusive of the existence of life on the planet. 

Scientist 1

This is the first evidence that organic life exists on Mars. On Earth, 95% of methane gas is produced by microbial organisms, which points towards the presence of similar biological processes on Mars. The rover has also found evidence of water bound to soil in the crater, and pictures showing carvings in the sides of the crater walls suggest the existence of once-flowing water. Because this water could have supported life in the crater, this methane originated from a bacterial source and shows there is life on the planet.

Scientist 2

There is no evidence of life on Mars. These methane spikes came from organic matter left behind from recent meteor impacts as they degraded in the sun's rays. Although the crater was once filled with water, now all water is bound to minerals in the soil and it not accessible. Methane has also been measured on planets such as Saturn, Uranus, and Neptune, which have conditions too hostile to support life. There is not even enough evidence to suggest that the original water in the crater could have supported life. 

Which of the following discoveries would support the claims of Scientist 2?

A rover on Mars tests the soil on the planet in Gale Crater. An instrument on the rover dectects steep spikes in methane levels in the soil within 60 days. Additionally, satellite measurements from the area detect unusual plumes of methane from this specific area, which scientists suggest may have once contained an ancient freshwater lake. Two different scientists discuss whether this evidence is conclusive of the existence of life on the planet. 

Scientist 1

This is the first evidence that organic life exists on Mars. On Earth, 95% of methane gas is produced by microbial organisms, which points towards the presence of similar biological processes on Mars. The rover has also found evidence of water bound to soil in the crater, and pictures showing carvings in the sides of the crater walls suggest the existence of once-flowing water. Because this water could have supported life in the crater, this methane originated from a bacterial source and shows there is life on the planet.

Scientist 2

There is no evidence of life on Mars. These methane spikes came from organic matter left behind from recent meteor impacts as they degraded in the sun's rays. Although the crater was once filled with water, now all water is bound to minerals in the soil and it not accessible. Methane has also been measured on planets such as Saturn, Uranus, and Neptune, which have conditions too hostile to support life. There is not even enough evidence to suggest that the original water in the crater could have supported life. 

In the paragraph concerning Scientist 1's opinion, he or she uses evidence of water having existed on Mars in the past to support the existence of life on Mars. How does Scientist 2 disagree with this?