Self-study
About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. ████ ██████████ █████ █████ ██████ ██ ███ ████████ ██ ███████ ███████ ███ ██████████ ████████ █████ ████ █████ ██████ ████ ███ ██████ ███ ██████ ██ ████ █████ ████ ██ ███████ ██████ ███████ ██████████ ███████ ███ ████████ ██ ██████ ████████ ██████ ████ ████████ ██ █ ███████████ █████ ████ ██ ███ █████ ██ ██████████ █████ ████ ██████ █ ███████ █████ ███ ████ ██ ██ █████ █████ █████ ████ ████████ ██████ ████ ██ ████ ███ ██████ ████ █████████ ██ ██ ███████ ██████████ ████ ███ █████ ██ ██████ ███████ ██ ███ ██████████ ███ █████████████ ██████ ████ ████ ██ ██ ██████
Summarize Argument
The author concludes that the level of carbon dioxide in the atmosphere was much higher 3 billion years ago than it is today. This is because we know that the ocean was liquid 3 billion years ago, and that required the level of greenhouses to be higher 3 billion years ago than it is today.
Notable Assumptions
The author assumes that if greenhouse gases were higher 3 billion years ago, carbon dioxide levels must have been higher 3 billion years ago. This overlooks the possibility that there were other greenhouse gases that were higher back then, while carbon dioxide levels stayed the same or were even lower.
25.
Which one of the following, ██ █████ ███████ ███ █████████
a
Sufficient heat to ████ ███ ██████ ██████ █ ███████ █████ ███ █████ ███ ████ ████ █████████ ███████ ██████████ █████████ ████ ██ ████████ █████████
We already know that greenhouse gases were higher 3 billion years ago, which is what helped keep the Earth warmer. The original source of the heat doesn’t change the fact that we know greenhouse gases were higher.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
b
Geological studies indicate ████ █████ ██ ████ ████ ███████ ██ ███████ ██████████ █████ ████ █████ ███ █ ███████ █████ ████
This raises the possibility that the greater levels of greenhouse gases 3 billion years ago were due to higher levels of methane. Carbon dioxide could have been equal or lower than it is today, because methane was higher.
Alternate explanation
Alternate explanation
Weaken: Introduce or support an alternate explanation for a phenomenon.
Strengthen: Helps to eliminate an alternate explanation for a phenomenon.
c
Geological evidence indicates ████ ███ ██████ █████████ ███████ ███████ ██ █████████ ████████ █ ███████ █████ ████ ███ ███ ██████ ██ █████ █████ ████████ ██████ ██████████████
We already know that the ocean was liquid and that this proves greenhouse gases were higher 3 billion years ago. The freezing point of water doesn’t change how we interpret these facts.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
d
The increase in ███ █████ ██████████ ████ ███ ████ █ ███████ █████ ███████ █████████ ████ ██ ██████████ ██████████ ██ ████ █████ ██ ██████
How the sun’s brightness correlates with the complexity of life is irrelevant. The argument concerns levels of greenhouse gases and whether higher levels of greenhouse gases imply higher levels of carbon dioxide.
e
Because the distance ████ █████ ██ ███ ███ ███ ███ ███████ █████████████ ████ ███ ████ █ ███████ ██████ ███ ████████ ██ ███ █████ ██████████ ███ ████████ ██ ████ █████████ ████████ ██████
We already know the Earth was liquid and that this proves greenhouse gases were higher 3 billion years ago. Levels of radiation don’t change these facts or how we interpret them. The argument concerns whether higher levels of greenhouse gases imply higher carbon dioxide levels.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).