What makes a tree a tree?

Will the world ever be ready for solar geoengineering?

The first time Frank Keutsch heard about solar geoengineering, he thought the idea was terrifying. To the Harvard University atmospheric chemist, schemes such as spraying millions of tons of sulfate particles into the sky to reflect the sun’s rays and cool the planet seemed perilous. Not only might the strategies disrupt the atmosphere in unexpected ways, but they might also dramatically alter the weather and harm the lives of Earth’s inhabitants.

China Is Building a Rain-Making System Three Times as Big as Spain

A cliff that changed our understanding of time

A rocky, remote outcrop in Scotland inspired the realisation that the Earth was millions of years old – and led Charles Darwin to his theory of evolution.