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[ptraye]

The first humans to enter the Americas arrived via a land bridge across the Bering Strait, and the most recent such land bridge formed about 25,000 years ago and disappeared about 7,000 years ago.

We can infer that...

1) The first humans to enter the Americas arrived over 7,000 years ago.

2) The first humans to enter the Americas arrived less than 25,000 years ago.

--------------------------------------------

the correct answer is #1. can someone explain why? they seem to be saying the same thing, but from different directions. please explain not only why 1 is correct but also why 2 is incorrect.

thanks.

[tommywallach]

Hey Ptraye,

Remember, we don't know that humans crossed on THIS land bridge (the passage only tells us that it's the most recent). However, that land bridge disappeared 7,000 years ago, so it's impossible that humans came less than 7,000 years ago. However, they could have come 100,000 years ago for all we know!

-t

[ptraye]

still, the argument or premises seem to be saying the same thing, but from opposite directions. formed, disappeared...

disappeared: they could not have arrived in less time than that, because there would be no land...

formed: they could not have arrived in greater time than that, because there was no land...

if you say, we don't know that humans crossed on THIS land bridge (the passage only says it's the most recent), i would say, we don't know that humans stopped crossing on another land bridge.

am i missing something?

[tommywallach]

Hey Ptraye,

Yes, you're missing that THIS land bridge formed. But we could have OTHER land bridges. If we know that the LAST land bridge disappeared 7000 years ago, then 7000 years ago is the most recent time that a crossing could have happened. But the 25,000 years ago number only relates to the "most recent" land bridge. Humans could have come over on OTHER land bridges, which might have existed EARLIER than 25,000 years ago.

Hope that makes more sense!

-t

[ptraye]

Tommy,

but that's not what it says. it says:
"the most recent such land bridge formed about 25,000 years ago and disappeared about 7,000 years ago."

so, we're talking about THE MOST RECENT bridge in both cases -- formed and disappeared.

if this was a could be true question type, i could understand your suggestion that "we could have OTHER land bridges." however, this is an inference question. and, the stimulus is talking about the same land bridge in both cases -- THE MOST RECENT.

if the wording was different or if it were a could be true question type, i could understand your position. am i still missing something?

thinking about it a different way, saying the most recent suggests there could be others, but it's not stated directly...

also, saying "we could have OTHER land bridges" could be true. however, we have no information about the formation times or disappearance of those other land bridges. it would be another assumption to suggest that those other bridges have the same form and disappearance times as the most recent land bridge.

should the stimulus be re-worded or is there sufficient information to understand why 1 is correct but 2 is incorrect?

also, we don't know that the LAST land bridge disappeared. we only know about the MOST RECENT.

[tommywallach]

Hey Ptraye,

You don't seem to be understanding. If I said, I started my final hamburger two hours ago and finished it one hour ago, I definitively know that I haven't had another hamburger in the last hour (because it was my FINAL hamburger). But I know nothing about any of the hamburgers I ate before that hamburger.

That's all that's going on here. The stimulus gives us information on the FINAL land bridge. So we know when the LAST person could've crossed it. But we know NOTHING about earlier land bridges, so we have no idea of knowing when the first person crossed ANY land bridge.

-t

[tommywallach]

And I'd remind you that YOU are the one whose inferring something. We don't know if other land bridges existed, so we can't say definitively whether or not people crossed over on them. You're inferring that there ARE NOT any land bridges. The stimulus only says that humans came over on a land bridge. We don't know if it was the most recent one.

-t