About 3 billion years ago

Answer choices

1. A

   Strengthens / Opposite11% picked this

   Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological

   This rules out a different way for the dimmer Sun to coexist with a liquid ocean.

   11%
2. B

   Correct57% picked this

   Geological studies indicate that there is much less methane in Earth's atmosphere today than there was

   Why this is right

   This lets us say, "Yes, author, there was a higher level of greenhouse gases 3 billion years ago, but that's because there was more methane, not because there was more CO2".

   Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

   57%
3. C

   Strengthens / Opposite13% picked this

   Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to

   Like choice (A), this rules out a different way that the dimmer Sun could coexist with liquid oceans.

   13%
4. D

   Out of Scope6% picked this

   The increase in the Sun's luminosity over the past 3 billion years roughly coincided with an increasing complexity

   Out of Scope: "increasing complexity of life" Nobody cares about the complexity of life, (D). We're just trying to solve the mystery of "how were the oceans still liquid if the Sun was dimmer?"

   6%
5. E

   Strengthens, if Anything14% picked this

   Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun's luminosity

   If the Sun were previously closer to the Earth, so that 80% as luminous still meant we were getting the same level of radiation we do nowadays, then that would have been an alternate explanation for how a dimmer Sun could coexist with a liquid ocean. But this answer rules out that possibility.

   14%