Q19 - A tree’s age can be determined

[lichenrachel]

I don't understand how C can help explain the relative age of the tombs. When the trees were planted and cut are unknown, right? Help needed! Many thanks.

[bbirdwell]

Tough question! Perhaps the key here is the term "relative ages."

The notion of the "age" of the trees is a red herring. The archaeologist's aren't trying to determine, for example, that the tombs are 450 years old or something. They are trying to determine the relative ages of the tombs -- that is, the age of the tombs in relation to one another (which tomb is oldest, second oldest, etc.).

We want an answer choice that helps explain how they were able to use tree rings to do this. We know that the tombs used freshly cut logs and that all the trees came from the same valley.

(A) says nothing about tree rings.

(B) says the trees in the valley are distinct from other trees. It seems close, but ultimately won't help us. We already know that the tombs were made from trees in the valley.

(C) helps. If each of the trees has this distinct pattern of 6, 3, 3, then we can use that pattern to judge the relative ages of the trees, and thus the relative ages of the tombs. For example, a tree with 10 rings after the distinctive set grew to be older than a tree with only 4 rings after the distinctive set.

(D) doesn't help us determine the relative ages of the tombs.

(E) doesn't help us determine the relative ages of the tombs.

[Shiggins]

(B) says the trees in the valley are distinct from other trees. It seems close, but ultimately won't help us. We already know that the tombs were made from trees in the valley.

I just want to make sure understand why this choice is wrong.

If these rings are distinct it still falls short of being able to make comparisons among the distinct rings from which the tombs were made.

[bbirdwell]

Yes! Especially age comparisons, which are needed here...

[anjelica.grace]

I can kind of understand why the correct answer choice is right and the other answer choices are wrong, but what about the case where a tree that was planted significantly earlier than another tree, say 40 years earlier, they both have the same distinct pattern, yet the tree planted earlier only has 1 ring after the pattern, and the other tree has 5 rings after the pattern. It would be determined that the other tree is older because it has more rings after the pattern despite that fact that it was just recently planted.

I'm just not fully convinced by having a similar base pattern that relative ages can be determined. It's like 4 people of different ages live through the same event and then comparing how long after this event each of them lives. Don't you also need to know when they were born?

[ManhattanPrepLSAT1]

Remember that we don't need to determine how old the trees are, but rather how old the tombs are. It is not possible for there to be 5 rings after the pattern on one tree and 1 ring after the pattern on another tree within the same tomb. All of the trees used for a tomb were cut down in the same year as the tomb was built. So if there were 5 rings after the pattern in the trees used to build one tomb and only 1 ring after the pattern in the trees used to build another tomb, then the one with 5 rings would have been built 4 years more recently than the tomb with trees with only 1 ring after the pattern.

I'm just not fully convinced by having a similar base pattern that relative ages can be determined. It's like 4 people of different ages live through the same event and then comparing how long after this event each of them lives. Don't you also need to know when they were born?

This would only be important if we were trying to establish the relative ages of the trees, but we're not. We're trying to figure out the relative ages of the tombs, and if all of the trees have this distinctive pattern, then the number of years since the pattern occurred would tell you how many years after that pattern each tomb was built - and thus their relative ages.

Hope that helps!

[coco.wu1993]

I don't really understand why C works. If one tomb was build exactly 12 years before another one. They should stay at the same stage of the distinctive sequence, but it does not mean they were build in the same year. Could anyone please help?

[yuchenh]

I think what c actually means is that trees have only one set of the unique 12 annual rings.

[christine.defenbaugh]

I don't really understand why C works. If one tomb was build exactly 12 years before another one. They should stay at the same stage of the distinctive sequence, but it does not mean they were build in the same year. Could anyone please help?

Great question coco.wu1993!

I think yuchenh has nailed it. (C) is not suggesting that there is a repeating pattern of 12 rings - if there were, you'd be absolutely correct. In that situation, two trees cut down 12 years apart would be indistinguishable in these circumstances.

What (C) is saying instead is that there is one distinctive 12 year sequence that all the trees share from the same 12-year weather event. A tree cut down 12 years after that event should have the weird pattern, and then 12 regular rings after it.

To use this to determine the relative ages, for example, the oldest tomb might have 3 regular rings after the weather event pattern, and the next tomb might have 7 regular rings after the weather event pattern. We'd then be able to tell that the two tombs were 4 years apart in age.

It would be like a note on each tomb saying "this tomb was built 3 years after the Weather Event" and "this tomb was built 7 years after the Weather Event"!

Does this clear things up a bit?

[coco.wu1993]

I think what c actually means is that trees have only one set of the unique 12 annual rings.

I don't really understand why C works. If one tomb was build exactly 12 years before another one. They should stay at the same stage of the distinctive sequence, but it does not mean they were build in the same year. Could anyone please help?

Great question coco.wu1993!

I think yuchenh has nailed it. (C) is not suggesting that there is a repeating pattern of 12 rings - if there were, you'd be absolutely correct. In that situation, two trees cut down 12 years apart would be indistinguishable in these circumstances.

What (C) is saying instead is that there is one distinctive 12 year sequence that all the trees share from the same 12-year weather event. A tree cut down 12 years after that event should have the weird pattern, and then 12 regular rings after it.

To use this to determine the relative ages, for example, the oldest tomb might have 3 regular rings after the weather event pattern, and the next tomb might have 7 regular rings after the weather event pattern. We'd then be able to tell that the two tombs were 4 years apart in age.

It would be like a note on each tomb saying "this tomb was built 3 years after the Weather Event" and "this tomb was built 7 years after the Weather Event"!

Does this clear things up a bit?

Got it! Thank you!

[smsotolongo]

Remember that we don't need to determine how old the trees are, but rather how old the tombs are.

It seems that you would have to determine the age of the tree to determine how old the tomb is. To me when they tell us that all the trees were from the same valley and the tombs were made out of fresh cut log they are setting it up. The trees from the same area would all have the same pattern as they were all effected by the same weather/climate pattern. The pattern would correspond to some time in history that we must be able to determine fairly accurately based on historical documents left by farmers or some other data. You have to assume that we know when this drought and rainy period occurred. Since all the trees are from the same area, the ring pattern is from the same 12 year pattern for all these trees. How many rings exist after the pattern tells us how many years after this pattern finished (that we know form historical sources) the tree was cut and that year the tomb was built. Did I take my assumptions too far?

[Mab6q]

Let me see if I can help the above poster. Try to back up and look at the main thing we are trying to figure out:

How did the Archaeologist determine the relative ages of the tombs by examining the rings of the trees.

Well, we know that rings determine age. And we get some other information about fresh cut logs from the P valley, which really isn't that relevant. Just because they were fresh cut logs doesn't mean they were all the same. If they figure that out, it does make it puzzling how they were able to figure out the tombs' relative ages. We are looking for an answer choice that provides us with a possibility.

A. who cares, nothing about age of tombs
B. This focuses on the last part about the P Valley, which is irrelevant. This might be helpful in a situation where only one of the tombs has these trees, but in this case they all are from the P Valley.
C. Gives us a way this could be possible. They all have a distinct sequence, so figuring out where that sequence falls in relation to the other rings would tell us which of the tombs are older. Interesting point is that we can't determine exactly how old each of the tombs is, just their relative ages.
D. nothing about the how.
E. out of scope.

[zen]

This is a tough one.

So the amount of rings corresponds to the age of trees. Researchers used the amount of rings in trees used to build tombs to determine the relative age of the tombs. The relative age of the tombs basically means how much younger or old are the tombs in comparison to one another,


A) Irrelevant. It does not mention the rings and just states the artifacts were preserved, This does nothing for us.

B) Does not help us. The stimulus already says all the trees came from the same valley, so we don't need that in the answer choice as it obviously does not help explain the discrepancy. Plus, just because the trees have uniform patterns that correspond to their distinct location does not explain how this can be used to determine the relative age of the tombs. We need to know more about the individual trees, not some general feature all the trees share.

D) Does not help us determine age of the tombs. If one tomb had a tree that was 90 years old and another tree that was 450 years old, how would we determine the age of the tomb? We would have a range 90-450 years ago but this would not allow us to figure out the relative age of the tombs to each other and that range of age seems to big to be useful for our purposes.

E) Irrelevant. Does not discuss the tree rings and artifact's age is irrelevant to age of the tomb.

Correct answer:

C) If each log in each tomb has a distinctive pattern that represents 12 distinct years, then we know that every single tree used to make the tombs lived at the same time as they all experienced this unique pattern of weather events. So maximum difference in age between two trees right until this unique weather pattern is 12 years. The amount of rings after the weather pattern can be used to determine the amount of years the trees lived after the weather pattern. If the trees are freshly cut and used then we know the rings we see indicate that they were used soon after they were cut so the rings are an accurate indicator of the trees' age. So if we can determine the logs used for one tomb are 200 years old and the logs for another tomb are 300 years old by looking at the rings, we can then determine the age of the trees and therefore the relative age of the tombs comprised of the trees.

Hope this helps someone ;p

[aaronwfrank]

D) Does not help us determine age of the tombs. If one tomb had a tree that was 90 years old and another tree that was 450 years old, how would we determine the age of the tomb? We would have a range 90-450 years ago but this would not allow us to figure out the relative age of the tombs to each other and that range of age seems to big to be useful for our purposes.

Also, even if we know the ages of the trees, we have no idea when they were cut into logs for tombs or buried for tombs. This is in addition to the fact that using the rings to determine relative ages is not discussed.

[GaurangP467]

I just have one query i.e. for answer (c) to work won't we have to assume that for building one single tomb only one single log was used or if there were multiple logs they were still from one single tree cut at around the same time ?