Ice Core Evidence — Reading Comprehension

Ice cores are essential scientific tools for understanding Earth's climate history. These long cylinders of ice are drilled from thick ice sheets in places like Antarctica and Greenland. Each layer of an ice core records information about the planet's past, making ice cores natural archives of the atmosphere. By studying ice cores, scientists can answer questions about how Earth's atmosphere and climate have changed over thousands of years.

How Ice Cores Trap Ancient Atmosphere

Snow falls on polar regions year after year, building up in layers. As more snow accumulates, the lower layers are compressed by the weight above, eventually becoming solid ice. During this process, tiny air bubbles are trapped between snowflakes. These air bubbles remain sealed as the snow turns to ice, preserving direct samples of ancient atmosphere within the ice. Scientists use special drills to extract ice cores that can be up to three kilometers long, with the oldest layers at the bottom. Each layer contains unique information about the time it formed, including temperature and greenhouse gas concentrations.

What Ice Cores Reveal: Temperature and CO₂

Ice cores provide two main types of evidence: past temperatures and atmospheric gas levels. Scientists measure isotopes of oxygen and hydrogen in the ice, which indicate the temperature when the snow fell. They also analyze the air bubbles for gases such as carbon dioxide (CO₂) and methane. Over the last 800,000 years, ice cores show that CO₂ levels naturally ranged between 180 and 280 parts per million (ppm). Today, CO₂ has reached about 420 ppm—a dramatic increase outside the natural range. The data also show a close connection between CO₂ and temperature: when CO₂ rises, global temperatures tend to rise as well.

Unprecedented Changes and Their Significance

The current rise in CO₂ is both faster and larger than any change seen in the ice core record. In the past, it took thousands of years for CO₂ to increase or decrease by 80 to 100 ppm. Now, CO₂ has jumped by over 100 ppm in just about 150 years, mainly due to human activities like burning fossil fuels. This rapid change affects climate systems, weather patterns, and sea levels worldwide. By studying ice cores, scientists can compare today's changes to natural patterns and highlight the urgent need to understand and address climate change.

Ice core research demonstrates how scientific evidence can reveal the deep connections between Earth's systems. It shows that human actions are now influencing the atmosphere at a scale that is clearly detectable in the geologic record.

Interesting Fact: The oldest ice core drilled so far comes from Antarctica and is estimated to be about 800,000 years old, containing bubbles of air from a time when Neanderthals walked the Earth.

What are ice cores mainly used for in scientific research?

Where do scientists usually collect ice cores?

What is trapped inside the layers of ice that makes ice cores so valuable?

Which gas in ice cores is directly linked to global temperature changes?

What does the term "isotopes" refer to in the passage?

Based on the passage, what causes most of the recent increase in CO₂ levels?

Why is the current rise in CO₂ considered unprecedented?

What is the natural range of CO₂ found in the ice core record for the last 800,000 years?

True or False: Ice cores can show how both temperature and greenhouse gas levels changed in the past.

True or False: Scientists use ice cores to find new animal species from the past.