Old Rocks, New Warming: Questions on a Canyon Road Trip

Compare past climate changes with today's warming and ask questions that evidence can answer.

Comparing changes

Read the passage and both tables, then answer the questions.

Questions at Vermilion Rim

1Over spring break, sixth grader Imani Castellanos and her uncle Desmond drove to three national parks in the Southwest. At Vermilion Rim, a made-up park based on real canyons in the region, the canyon walls show hundreds of meters of rock layers stacked like pages in a book. Imani kept a journal of questions during a ranger talk and at the visitor center.

2Ranger Farid Lindgren pointed out two layers. One is limestone full of fossil shells and corals, much like animals that live in warm, shallow seas today. Another is sandstone with long, slanting lines like the sides of desert sand dunes. These layers formed over many millions of years. The region's climate changed partly because the continent itself moved: plates drift only a few centimeters a year, but over 300 million years that adds up to thousands of kilometers. A thin layer of volcanic ash shows that a large eruption once dropped ash over the area.

3"Earth's climate has changed many times," the ranger said. "Scientists ask what is causing a change and how fast it is happening." Slow changes in Earth's orbit and in the tilt of its axis help start and end ice ages over tens of thousands of years. The Sun's energy output rises and falls a little in cycles of about 11 years. A very large volcanic eruption can put tiny particles high in the air that block some sunlight and cool Earth for a year or two.

4People also affect climate. Burning coal, oil and gas releases carbon dioxide (CO₂), and clearing forests adds more. CO₂ is a greenhouse gas: it traps heat near Earth's surface. Since 1958, scientists have measured CO₂ in air samples directly. For older times, they measure CO₂ in tiny bubbles of air trapped in ice sheets, some of it hundreds of thousands of years old. Thermometers have tracked Earth's temperature since the late 1800s, and satellites have measured the Sun's energy since the late 1970s.

Table 1. Visitor Center Poster: Changes in Earth's Average Temperature
Event	When	Temp. change (°C)	Time it took
End of the last ice age	20,000 to 10,000 years ago	Rose about 5	About 10,000 years
After a very large eruption	Several recent examples	Fell about 0.3, then recovered	About 2 to 3 years
Since 1900	1900 to 2020	Rose about 1.2	120 years

Table 2. CO₂ in Earth's Air
When	CO₂ (ppm)	Measured in
20,000 years ago	190	Ice bubbles
10,000 years ago	260	Ice bubbles
1800	280	Ice bubbles
1900	296	Ice bubbles
1960	317	Air samples
2020	414	Air samples

Use Table 1. To compare rates, divide each temperature rise by the number of hundreds of years it took. Do not round.

At the end of the last ice age, Earth warmed about °C per 100 years. Since 1900, it has warmed about °C per 100 years.

Use Table 2.

From 1900 to 2020, CO₂ in the air rose by ppm. From 20,000 years ago to 10,000 years ago, it rose by ppm.

Which statement best describes Tables 1 and 2 together?

A. Temperature has fallen since 1900 while CO₂ has risen, so the two changed in opposite directions.
B. CO₂ rose faster at the end of the ice age than since 1900, while temperature rose more slowly then.
C. Temperature and CO₂ both rose at the end of the ice age, and both have risen much faster since 1900.
D. CO₂ stayed near 280 ppm from 20,000 years ago until 1960, then jumped up to 414 ppm.

Imani saw the ash layer and asked whether volcanoes could explain the warming since 1900. What do Table 1 and paragraph 3 suggest?

A. Eruptions are a likely cause, since the ash layer shows an eruption reached the canyon.
B. Large eruptions cooled Earth for a few years, so they do not explain a century of warming.
C. Large eruptions cooled Earth for about 120 years, so they slowed down today's warming.
D. Eruptions are a likely cause, since a very large eruption warmed Earth by about 0.3 °C.

Asking good questions

Help Imani choose and sort questions for the ranger.

Use paragraphs 2 and 4. Sort each of Imani's questions by the kind of evidence that could best answer it.

Was this area once covered by a warm, shallow sea?How much CO₂ was in the air 20,000 years ago?Has the Sun's energy output changed since 1980?Did an eruption long ago drop ash on this area?How much CO₂ was in the air in the year 1800?How much has Earth's average temperature risen since 1900?

Rock layers and fossils	Air bubbles in ice	Modern instruments

Uncle Desmond wonders whether drifting continents could explain the warming since 1900. Which question would best test his idea?

A. How far do continents move in 100 years, and could that warm the planet?
B. Were the ancient sand dunes taller than the desert dunes found today?
C. How many millions of years did the limestone layer take to form here?
D. Which layer in the canyon wall holds the most fossil corals and shells?

Which question can be answered with the data in Table 2 alone?

A. Will the CO₂ in the air reach 500 ppm by the year 2060?
B. Which country released the most CO₂ into the air in 2020?
C. How warm was the sea when the canyon's limestone formed?
D. Did CO₂ rise more from 1900 to 2020 than from 1800 to 1900?

Use paragraphs 2 and 3. Match each factor to the length of time over which it changes climate.

Drifting continents
Changes in Earth's orbit and tilt
Ups and downs in the Sun's energy
A very large volcanic eruption

A. Tens of thousands of years
B. A year or two
C. Many millions of years
D. Cycles of about 11 years

Imani wants a follow-up question that would best help show whether the extra CO₂ since 1900 comes mainly from people. Which question is best?

A. How much CO₂ do burning fuels and clearing forests release each year, compared with volcanoes?
B. Did the Sun's energy output rise or fall between 1900 and 2020, and by how many W/m²?
C. Was the CO₂ in the air lower 20,000 years ago than it was in 1800, before modern factories?
D. How much carbon is stored in the canyon's limestone layers, which formed in ancient seas?

10.

Uncle Desmond says, "The limestone shows this place was warm long before people, so today's warming is just another natural change." Do you agree? Write a claim, use data from both tables, and explain your reasoning. Then write one new question you would ask the ranger to test your claim.