Fossil Ferns, Coal and a Volcano: Asking About Warming

Ferns in the Coal

1Ms. Ilse Becker's sixth graders spent a day on a geology field trip. In the morning they toured the Black Creek Coal Museum, an old mine that now welcomes visitors. In the afternoon they collected rocks and fossils at a road cut nearby. In a layer of gray shale just above a thin band of coal, Zainab Yusuf split open a rock and found the print of a fern leaf.

2The museum guide explained that much of the world's coal formed from plants that grew in swamps more than 300 million years ago. When the plants died, they were buried under mud and sand before they could rot away. Over millions of years, heat and pressure turned the buried plant material into coal. While they were alive, those plants took in carbon dioxide (CO₂) from the air, so coal holds carbon that was removed from the air long ago. Burning coal, oil or natural gas releases that carbon as CO₂, which is a greenhouse gas. Greenhouse gases absorb some of the energy given off by Earth's surface and send part of it back down.

3The last room of the museum showed that Earth's average surface temperature has risen by about 1 °C over the past century. Caleb Moreau stopped at a smaller display about the 1991 eruption of Mount Pinatubo in the Philippines. The eruption blasted ash and gases high into the atmosphere. There, the gases formed tiny droplets that spread around the planet and reflected some sunlight back to space. Caleb wondered whether volcanoes could explain the warming.

4Back at school, Ms. Becker reminded the class that a scientific question can be answered with evidence, such as measurements, and that a good question names what to measure or compare. She asked each student to write questions about the factors that may have caused the warming and to say which data could answer them.