Hundreds of thousands of scientists and their colleagues are writing public letters, signing petitions and planning to march on Washington, D.C. and other U.S. cities on Earth Day because they see a growing war on science in the Trump administration.

The idea for the science march began with posts on Reddit, and has now attracted more than 600,000 followers on Twitter (@ScienceMarchDC) and Facebook. The mobilization has stunned many in the scientific community.

Why this matters: Scientists usually stand clear of political fights. They let the politicians, activists and pundits wage public battles. This response was was clearly influenced by the recent women's march, where the sizes of the crowds in every big city in the country were triple or quadruple estimates by organizers.