EARTH, WORLD AND UNIVERSE: THREE MUSKETEERS OF COSMOS

The ultimate single-word term that encompasses all of these nested scales—from our home planet to the totality of existence—is the cosmos. While "earth" names our specific rocky globe, "world" often includes human society and life upon it, and "universe" describes all physical matter and space, cosmos uniquely denotes the entire system as an orderly, harmonious, and unified whole. The Earth is an oblate spheroid (and more precisely a lumpy geoid), while the observable universe has a nearly flat geometry on a large scale. Earth refers specifically to our physical planet, while the World encompasses the planet along with human society, culture, and life. Earth is the third planet from the Sun and the only astronomical object known to harbour life. This is made possible by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its ocean, which covers 70.8% of Earth's crust.