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

Hm. I see your point!

Wait... no. No, I don't. Moving on...

Question 3

The author describes the method in the first paragraph and then, in the second paragraph, explains a couple limitations of that method. The author does not imply that the method is invalid or that it should not be used. Rather, the author explains how climatic conditions can be deduced from tree-ring patterns and then describes conditions under which that method would not be reliable. In other word, the author believes that the method is valid but that it doesn't work under certain circumstances.

So the main purpose is to describe how (and under what conditions) the method can be used, not to question the validity of the method.

So choice (C) is more accurate than choice (B).

I hope this helps!
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Passage breakdown

In the first paragraph (P1), the author describes a method to learn about past climatic conditions

• Dendrochronology, or "the study of tree-ring records to glean information about the past."

In the second paragraph, the author lists several limitations of the method introduced in P1.


For more on the process of breaking down RC passages, check out this article and our live RC videos.

Explanations for individual questions

• Question 1
• Question 2
• Question 3

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Took 6 mins 10 seconds , including 2 mins to read the passage

-The author talks about a certain study that can be used to determine climatic conditions
-The study also talks about how aging is related to the number of rings a tree has
-The author does not offer an opinion and is merely stating facts



1.
"And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count."
The rings of trees are used to determine the age of the trees and since there are no rings appearing on trees in dry regions, we cannot be sure on the age of the tree and hence there will not be a perfect correlation between age of tree and number of rings. Hence option (E)

2.
―Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions"
For 2 trees to be correlated they should have common features arising from their ring patterns which eventually indicate the climatic condition they grew in. Option (A) clearly states this point and hence is the right answer.

3.
The author is clearly concerned with determining how rings on trees can be used to predict past climactic conditions

Answer C
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In 2:55 minutes,
The rings are the main clues for understanding the age of a tree, the various shapes of the rings formed changes with the change of weather (water supplied to it, in different climatic condition).So, clearly it triggers the fact that the rings are the only link to find the age and if due to some reason the rings are uncertain to figure out by the researchers then it brings lack of correlation , i.e tree rings and its age.

In opening line it says "Dendrochronology, the study of tree-ring records to glean information about the past, is possible because each year a tree adds a new layer of wood between the existing wood and the bark."-------means every year tree adds a new layer (ring)

In last but one line it says "And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count." ------means the regular pattern of "one ring per year" phenomenon may be not shown due to extremely dry weather.

So if scientists count the age of tree by counting number of rings and if the tree is having sometimes two rings in a year or no ring at all in any given year, this may lead to wrong age determination of the tree.


Hence E.

HTH

Why B is wrong ?
Clearly, the second paragraph is questioning the validity of method explained in first paragraph.

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

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.

I didn't understand this answer.

Passage states something about dead tress of different, but overlapping, ages.

How can a question ask about trees in general that grew in the same area and that were of different, but overlapping, ages.

So how about answering this one then?

Time taken: 05:10mins

1. 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.Sort of. But the option is too wide in scope. This option adds climate conditions and a lot more in "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.No we need both the trees to be alive to analyse climate conditions
C. The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.Its not necessary to be the same species
D. The rings corresponding to the overlapping years could not be complacent rings.They can be
E. The rings corresponding to the overlapping years would provide a more reliable index of dry climate conditions than of wet conditions.Correct.


2. In the highlighted text, "uncertainties" refers to
A. dendrochronologists' failure to consider the prevalence of erratic weather patternsUncertainty is wrt the determination of age of tree in years of drought or sporadic growth spurts
B. inconsistencies introduced because of changes in methodologyThere is no mention of change in methodology
C. some tree species' tendency to deviate from the normSort of. But this makes it sound like the tree deviates intentionally. Sometimes, like in cases of drought, trees are compelled to introduce inconsistent ring patterns.
D. the lack of detectable variation in trees with complacent ringsNope
E. the lack of perfect correlation between the number of a tree's rings and its ageYes. Sometimes due to climate or owing to the species that the tree is, there is inconsistencies with the tree-ring patterns.


3. The passage is primarily concerned with
A. evaluating the effect of climate on the growth of trees of different speciesWe are not discussing different species here.
B. questioning the validity of a method used to study tree-ring recordsWe are not questioning anything. It is just a description of the method
C. explaining how climatic conditions can be deduced from tree-ring patternsCorrect.
D. outlining the relation between tree size and cell structure within the treeThere is no mention of tree-size contributing to ring formation. Only age is introduced as a factor.
E. tracing the development of a scientific method of analyzing tree-ring patternsWe do not have any explanation of history of method of analysing tree-ring patterns

1. 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.

Ans - D

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.

2. 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

Ans - D

First paragraph states how temperature and climate systematically affect tree growth. Start of second paragraph states that 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. So these trees don't exhibit the typical variations due to climate and temperature changes that trees would normally exhibit.

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

Ans - C

Author outlines how the methods of Dendrochronology are used and in second paragraph he mentions certain limitations of their applicability.

That is the reason why the author is saying that ring patterns are corroborated among trees and conclusion about climatic conditions can be arrived at. There will be differences between two trees, but majority will exhibit the similar pattern and that is what Option A) is saying.
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Can someone explain?
I don't see how C Is the main point.
First dendrochronology was introduced and then it was questioned in the second paragraph.
if you take C as the answer it is missing the most of the second paragraph.

hi,
I chose D for Q2. Please help why is it E?
Also, I didn't understand Q1.

thanks in advance

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 1960 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 1910 - 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.

Hopefully that helps you arrive at the correct answer!


The highlighted portion specifically refers to trees that may go a year or two without adding rings. According to the first paragraph, it is often possible to determine a tree's age by counting the rings. Why? Because there is typically an annual boundary line at the end of the growing season. With a regular annual growth pattern, you can count the rings to determine the age.

But what if a tree goes a year or two without adding any rings? In that case, if you count the rings to determine the age, your number will be LESS than the tree's actual age. For example, if you count 40 rings, the tree could actually be 41, 42, 45, 50, or 60+ years old! We would have no way to determine the number of years in which rings were not added. This corresponds to choice (E).

As for choice (D), the highlighted portion refers to the uncertainty in ring count, not to the lack of variation in ring width in complacent trees. We are indeed told that trees with "complacent" rings show little variation in ring width from year to year. However, you should still be able to count rings to determine the AGE of complacent trees. You would not be able to tell which years were wet/dry, but you should still be able to determine the age.

Choice (E) is the best answer.
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Hi GMATNinja

I don't quite understand the example you mentioned in your post.

"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)"

If one tree died in 1940, and the other was born in 1950, then it would be a 10 year short instead of a 10 year overlap.

Am I correct?

P1 - about D, how rings form in diff condition.
P2 - what if no change in climate; uncertainties;
Main point - explained D, impact of weather on rings, and uncertainties.
Tone - informative.

1. In the highlighted text, "uncertainties" refers to
pre-think - due to dry condition, how rings are not added.

(A) dendrochronologists' failure to consider the prevalence of erratic weather patterns - no
(B) inconsistencies introduced because of changes in methodology - no; changes in methodology- wrong
(C) some tree species' tendency to deviate from the norm - true but not the answer.
(D) the lack of detectable variation in trees with complacent rings - no
(E) the lack of perfect correlation between the number of a tree's rings and its age - yes; because of uncertainties introduced.

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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?

Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions

(A) The rings corresponding to the overlapping years would often exhibit similar patterns. - has to be this
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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 - evaluating is +/- of something.
(B) questioning the validity of a method used to study tree-ring records - questioning is only a part.
(C) explaining how climatic conditions can be deduced from tree-ring patterns - not perfect but covering most of the passage. use of vocab is also moderate "explaining".best of the lot.
(D) outlining the relation between tree size and cell structure within the tree - sub part of P1
(E) tracing the development of a scientific method of analyzing tree-ring patterns - tracing the development of a scientific method --- well not working on a method.
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"The rings corresponding to the overlapping years could not be complacent rings." what's the meaning of this complacent rings??

GMATNinja

For Question2:

Basis this line in the passage "Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again."

Shouldn't the answer be :
(C) The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.

As (A) does not talk about any species?

hi SajjadAhmad, u1983, GMATNinja, GMATNinjaTwo, workout, Gnpth

what's the problem of the B in Q3?

IMOP, P1 states general patterns of rings under different environments,
while, P2 says patterns are similar under certain environment, and under some other certain environments, pattern has "uncertain" pattern, question the accuracy of the age if count the rings.
because I think Q2 questions the patterns, so I picked up B,
I think C does not include what P2 says, so I cross off C
I saw B is the second ranking, suggesting not few people agree with B.

all correct and in 7m12s. thank you for posting.