TOEFL ITP Reading set 028
Reading Comprehension practice — read the passage and choose the best answer.
ตัวแทนภูมิอากาศโบราณจากแกนน้ำแข็ง
- Line numbers appear every 5 lines.
- Answer all 10 questions, then choose ตรวจคำตอบ to see the Thai translation, score summary, and explanation.
- Use Previous / Next to open the previous or next practice set.
Paleoclimate researchers treat ice cores as layered archives
of past atmosphere. Each year's snowfall compresses into ice
that traps tiny bubbles of ancient air, along with dust, ash,
and chemical traces that record temperature, volcanic
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eruptions, and greenhouse-gas levels. Drilling teams recover
long cylinders from Greenland and Antarctica; the deepest
cores span hundreds of thousands of years and preserve
seasonal bands that scientists count much as tree rings are
counted. Oxygen isotope ratios in the ice itself serve as a
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proxy for local temperature: colder periods leave a distinct
isotopic signature that can be calibrated against modern
measurements. Bubbles sealed in the ice allow direct sampling
of past carbon dioxide and methane concentrations, revealing
how greenhouse gases rose and fell across glacial and
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interglacial cycles. Dust layers and volcanic ash horizons
help synchronize cores from distant sites and date abrupt
climate shifts. Still, ice-core proxies are not perfect
thermometers. Gas bubbles may close decades after the snow
fell, so air ages can lag ice ages; melt layers can blur
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seasonal signals; and sparse drilling sites leave large
regions of Earth's past climate poorly sampled. Near the
surface, porous firn delays bubble closure, which analysts
must model before matching gas records to ice layers. At
greater depths, annual layers thin until researchers rely on
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ice-flow models and volcanic markers rather than direct
counting alone.
Researchers therefore combine ice-core records with marine
sediments, lake varves, and corals to build broader
reconstructions. Policy debates about future warming often
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cite these archives because they show that current
greenhouse-gas levels exceed those measured in ice spanning
several glacial cycles. Understanding how proxies are
formed, dated, and cross-checked helps readers judge climate
claims that rest on paleoclimate evidence rather than on
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weather anecdotes alone. In short, ice cores turn frozen
snowfall into one of the most continuous natural records of
Earth's climate history available to science.