Dendrochronology, the study of tree-ring records to glean information

Hi GMATNinja,

Your explanation is very detailed and helpful.

I have 1 query regarding interpretation of the phrase overlapping ages. I understand that overlapping ages are the years in which both trees would be in existence. Whereas your explanation of question 1 suggests that overlapping ages are the years in which neither of the 2 trees exist, i.e. 1940-1950.

Can you please clarify the meaning of the word overlap in the context of the passage?

Thank you.

Can sb tell me which one (E) (A) (C) (D) is correct??? As I saw on the forum, different person post different answer????



(A)
For the first question, refer to the following portion: "In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions."

So if we look at the ring patterns of dead trees, we should be able to tell which years were dry and which years were wet based on the width of the rings. If we only have one tree, then we would obviously only be able to gather data for the years in which that tree was alive. But now imagine we have two trees. One of the trees died in 1940 at the age of 50, and the other was born in 1950 and lived for 60 years (a 10 year overlap). In that case, we would have ring data from 1890 - 2010 and could use that data to help figure out which years were wet and which were dry.

Now consider the 10-year overlap. Because we are talking about different trees, the actual widths of the rings from those years might not be exactly the same. However, during wet years, we would expect RELATIVELY broad rings. During dry years, we would expect relatively narrow rings. So even though the precise widths might not be exactly the same for both trees, the PATTERNS (i.e. narrow-narrow-broad-narrow-broad-broad-broad-etc) will likely be the same. Now the second paragraph does explain why this is not ALWAYS the case, but the passage suggests that the patterns will OFTEN exhibit similar patterns.

A very good and detailed explanation, thanks GMATNinja
(OA) gives this one as correct answer

However if we see from the last sentence of paragraph2
Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.

So shouldn’t that we also need to take into account certain “species” to determine whether they exhibit “similar pattern”?????


(C)
We can infer from sentence as below
“Certain” species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.
-not “every” species
So it’s possible that even if they were different species, maybe “the rings corresponding to the overlapping years would exhibit similar patterns.”
-hence incorrect

(D)
However, its plausible for this explanation written by desaichinmay22
I also have a way of thinking same as desaichinmay22



In the passage it is stated that often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions. Start of second passage states that "complacent" rings tell nothing about changes in climate. Hence it can be deduced that rings corresponding to overlapping years couldn't be complacent rings.

So why (D) cannot be the correct answer???

Or maybe it(the rings corresponding to the overlapping years) could be “complacent” rings, but it cannot tell anything about changes in climate????


(E)
Its obviously incorrect, since from the second passage

However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate. And trees in extremely dry regions may go a year or two without adding any rings,

- hence we can infer that “steady wet” &“extremely dry” tell nothing about changes in climate

So (E) The rings corresponding to the overlapping years would provide a more reliable index of dry climate conditions than of wet conditions.-obviously not correct

Why (B) cannot be correct answer???
I have the same problem as zoezhuyan

we can see from the first word “however” in para2, doesn’t it indeed “ question” the validity of Dendrochronology,a method to study the tree-ring records for gleaning information about the past, in para1???

We can easily see from this passage that (C) correspond to para1’s main idea, and for (B), it correspond to para2

Or maybe we can think for another way, it is that—which one, para1 or 2, is this passage’s main focus???however, its not quite obvious in this whole passage for us to discern which one is the main focus
so in Q3, it just hard for us to choose between (B) and (C)

When answering "main idea" questions on RC, looking for the answer choice that "covers what all the paragraphs said" will cause you endless frustration and often lead you to the wrong answer choice.

That's because the question is not, "Which answer choice seems to cover the content of every paragraph?"

Rather, the question is, "Why did the author write this passage in the first place?"


Again, why did the author write the passage?

• The author wrote P1 in order to introduce the technique of dendrochronology and show how this method can reveal past climate conditions.
• The author wrote P2 in order to explain a few scenarios where dendrochronology's results can be compromised. In other words, the author wrote P2 to qualify the statements made in P1, rounding out the overall explanation of how dendrochronology works.

The author wanted to explain how dendrochronology can be used to deduce climate history (including when it might not work).

Let's take a look at choice (B) one more time:


Did the author write this passage in order to question the validity of a method?

Nope. While reading P2 in isolation might lead us to choose (B), remember that the reason the author wrote P2 in the first place is to expand on P1. None of the language here signals a desire by the author to convince us that these exceptions should make us question the validity of dendrochronology overall.

The overarching purpose is to present a well-rounded explanation of how and when it works. When it might not work is presented as part of that explanation, not a challenge to the method's validity.

That's why choice (C) is the best fit and choice (B) can be eliminated.

Whoops! Thank you both for catching my careless arithmetic error.

Yes, I plugged in incorrect numbers to illustrate the logic of the passage. While the underlying reasoning is identical, I've updated my post to correct this mistake on the figures. Sorry for causing this confusion!

"Uncertainty" is about the age of trees. We already know that they have already deviated from the norm, from that we have an uncertainty of the age.
We can get it from the last line from the last paragraph "ages can be correlated to provide an extended index of past climate conditions." Ages can be correlated from the rings, but when there is an uncertainty about the age of the trees.

When I read the sentence complacent rings, I thought of meaning as similar. But on checkingdictionary.com I found the meaning as : self-satisfied, pleased .

I don't see similar or synonyms of similar in complacent meaning list.
Can someone give his/her opinion on meaning of D with the dictionary meaning?

Hi imSKR,

Dictionary meaning of Complacent: showing smug or uncritical satisfaction with oneself or one's achievements.
Other synonyms in addition to ones you have mentioned are lazy, slack.

Now w.r.t the passage, it would mean slow changes in the rings or no changes at all, as also mentioned in the last para:
However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate.

Hope This Helps.
Thanks.

Hi VeritasKarishma GMATNinja bm2201

Can you please give your opinion on Q1: why not D

And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count.
What I understand:
Add no rings then it will be difficult to calculate the age.

If No rings then what happens ? Then we get wrong count of rings. It means lack of something ( ring) that could have been considered to determine the age.
so what is uncertainity to the count here? I think uncertainity count means somethign that was detectable ( such as ring)





So I choose D. lack of something visible that could have added in the count to compensate missing count of rings.

Please suggest VeritasKarishma GMATNinja bm2201

1. In the highlighted text, "uncertainties" refers to

(A) dendrochronologists' failure to consider the prevalence of erratic weather patterns
(B) inconsistencies introduced because of changes in methodology
(C) some tree species' tendency to deviate from the norm
(D) the lack of detectable variation in trees with complacent rings
(E) the lack of perfect correlation between the number of a tree's rings and its age


However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate.
And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count. Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.


Complacent rings appear in trees with steady supply of ground water. So climate has no impact on their rings.

The "uncertainties" mentioned refers to an inability to determine the exact age because in very dry regions (These trees do not have steady supply of ground water and hence have no complacent rings), trees may skip adding any rings in some years. Hence, it refers to the lack of perfect correlation between the tree's rings and its age.

hello ma'm VeritasKarishma

So here the count refers to this perfect correlation ?( perfect correlation between the tree's rings and its age)
uncertainty == lack

please confirm

Yes. Since the trees add 1 ring every year, we can count the rings to get their age. But if they skip adding rings some years, the perfect correlation goes for a toss.

Actually I don't understand much highlighted in red. what controls ? Who who?

Anyways, thanks for the definition.

Read Time : 4 mins
Correct : 3/3

Passage Pattern: Defination>Its importance>Pattern of tree rings and its indication>Some variation due to affecting parameters

Paraphrazing:
Definition and its speciality: Dendrochronology
Pattern of layer formation:
• In temperate and subpolar climates: the new cells that develop are smaller and thick-walled
• In wet years rings are broad;
• In drought years they are narrow
• Ring patterns of dead trees of different can be correlated to provide an extended index of past climate conditions.
Comparison:
- Trees that grew in areas with a steady supply of groundwater
- Trees in extremely dry regions
- Certain Tree species sometimes

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1. In the highlighted text, "uncertainties" refers to
(A) dendrochronologists' failure to consider the prevalence of erratic weather patterns
(B) inconsistencies introduced because of changes in methodology
(C) some tree species' tendency to deviate from the norm
(D) the lack of detectable variation in trees with complacent rings
(E) the lack of perfect correlation between the number of a tree's rings and its age

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2. The passage suggests which of the following about
the ring patterns of two trees
that grew in the same area and that were of different, but overlapping, ages?


(A) The rings corresponding to the overlapping years would often exhibit similar patterns.
(B) The rings corresponding to the years in which only
one of the trees was alive would not reliably indicate the climate conditions of those years.
(C) The rings corresponding to the overlapping years would exhibit
similar patterns only if the trees were of the same species.
(D) The rings corresponding to the overlapping years could not be complacent rings.
(E) The rings corresponding to the overlapping years
would provide a more reliable index of dry climate conditions than of wet conditions.

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3. The passage is primarily concerned with
(A) evaluating the effect of climate on the growth of trees of different species
(B) questioning the validity of a method used to study tree-ring records
(C) explaining how climatic conditions can be deduced from tree-ring patterns
(D) outlining the relation between tree size and cell structure within the tree
(E) tracing the development of a scientific method of analyzing tree-ring patterns

How long are these practice passages taking other users? Is 10 minutes too long?

Time taken 4 min 50 sec. Got 2 correct and 1 incorrect