Slowly, oxygen filled the atmosphere. The sky turned blue. The ozone layer formed, shielding the land from the sun’s deadly ultraviolet rays. Finally, life could crawl onto land.
One of those planets was .
Long ago, before there was time, space, or a single star, there was nothing. Not even empty space. Then, about 13.8 billion years ago, something miraculous happened: . the universe and the earth 7th class pdf
You can copy and paste this text into a PDF or a document to save as a PDF. Chapter 1: The Beginning of Everything Slowly, oxygen filled the atmosphere
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. Finally, life could crawl onto land
For millions of years, the universe was a dark, foggy soup. But gravity, the universe’s invisible glue, started pulling clumps of gas together. These clumps became the first stars, brilliant furnaces that lit up the cosmos. Some stars lived fast and died young, exploding in supernovas that scattered heavier elements like carbon, oxygen, and iron across space. These were the seeds of future planets.
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.