Auroras paint the night when charged particles from the Sun stream along Earth’s magnetic field and collide with gases high in the atmosphere. Oxygen can glow green or red, while nitrogen can shine pink or violet. These colors ripple like curtains because the solar wind is uneven and Earth’s magnetic field guides particles in arcs. Auroras appear most often near the poles, yet strong solar storms can push them to lower latitudes, giving more people a chance to witness this natural light show.
Comprehension Check
What causes the colors in an aurora?
Why are auroras most common near the poles?
Coral Reefs: Cities of the Sea
Coral reefs form when tiny animals called polyps build skeletons of calcium carbonate that stack into ridges, caves, and towers. These structures create shelter and feeding spaces for fish, turtles, and countless invertebrates, making reefs some of the most diverse ecosystems on Earth. Warm, clear, shallow water and steady sunlight help corals grow, but extreme temperatures or pollution can stress them. When conditions improve, young corals can recolonize damaged areas and rebuild the reef city over time.
Comprehension Check
What do coral polyps build that becomes the reef’s structure?
Which condition best supports coral growth?
Waterfalls: Sculptors of Stone
A waterfall forms when a river drops over a ledge of hard rock onto softer layers below. Falling water erodes the base and carves a plunge pool, while the top edge slowly retreats upstream. Mist from the impact can support unique plants, and the roar of the falls hints at the energy being released. Over long periods, waterfalls reshape valleys and leave behind curved cliffs and terraces that record the history of flowing water through the landscape.
Comprehension Check
Why does the edge of a waterfall move upstream over time?
What landform is carved by the impact of falling water?
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