Earth Science
What Is the Water Cycle, and How Does It Work?
The water in your glass has fallen as rain, sat in ancient oceans, and drifted through clouds countless times. The water cycle is the vast, sun-powered engine that keeps recycling it. Here is how it works.
What Is a Fossil, and How Does One Form?
A fossil is a message from deep time, a bone or a footprint turned to stone and waiting millions of years to be read. Here is what a fossil actually is, how one forms, and why so few living things ever become one.
What Is the Greenhouse Effect, and How Does It Work?
The same effect that makes Earth warm enough to live on is also driving climate change. Here is how the greenhouse effect works, and how a good thing tipped out of balance.
Why Is the Ocean Salty? The Science of Seawater
The rivers that feed the ocean run fresh, yet the sea is salty. Here is where all that salt comes from, how much there is, and why it keeps piling up.