Fast-forward billions of years to a quiet corner of a spiral galaxy we call the . A medium-sized, yellow star was born—our Sun . Around it swirled a disk of gas and dust. In this disk, tiny dust grains stuck together like snowballs, growing into pebbles, then boulders, then mountains, and finally planets.
From the outside, Earth looks like a blue marble. But inside, it’s still restless. The crust is broken into giant puzzle pieces called . They float on the hot mantle, grinding together to build mountains, pulling apart to create valleys, and causing earthquakes. the universe and the earth 7th class pdf
At first, Earth was a nightmare: a molten ball of lava, constantly bombarded by comets and asteroids. It had no air, no water, just fire and rock. But over millions of years, Earth cooled. A thin, rocky crust formed on its surface. Heavier metals like iron and nickel sank to the center, creating a dense . Lighter rocks formed the thick mantle and the thin crust where we live. Fast-forward billions of years to a quiet corner
