Ice cores, archives of ancient air

In the picture

1. 1Trapped air bubbles: real samples of past atmosphere, with their CO2 concentration
2. 2Pale layers: yearly snowfall bands that let scientists count back in time near the top
3. 3Deep, clear ice: older ice under huge pressure, holding air hundreds of thousands of years old
4. 4Drill rig: brings up the core section by section from more than 3 km down

Examples

• Ice cubes from the freezer often have cloudy bubbles of air trapped as the water froze.
• Old snow at the bottom of a heap is packed harder and icier than fresh snow on top.

Quiz: Ice cores, archives of ancient air (Age 17)

1. 1

   Over the last 800,000 years, between which levels did atmospheric CO2 swing, according to ice cores?

   • About 100 ppm in ice ages and 180 ppm in warm periods
   • About 280 ppm in ice ages and 420 ppm in warm periods
   • About 180 ppm in ice ages and 280–300 ppm in warm periods
2. 2

   What do ice cores show about CO2 and temperature across glacial cycles?

   • When CO2 rises, temperature falls
   • They rise and fall together
   • Temperature changes while CO2 stays almost constant
3. 3

   Why does each layer of polar ice hold a sample of the atmosphere from when it formed?

   • Falling snow compresses into ice and seals off pockets of the air above it at the time
   • Gas released from the bedrock rises and gets trapped in the ice
   • Modern air seeps down through cracks and mixes into the older ice

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.