Scientists in cities around the globe are celebrating Earth Day by taking to the streets to defend their work from the heightened political attacks of the anti-science Trump administration.

Saturday’s marches in over 600 cities around the world—including a massive march in Washington, D.C.—mark an unprecedented mobilization of researchers and experts who are fighting back against President Donald Trump’s war on science.

Indeed, for many scientists involved, taking part in a March for Science is their first collective political action. Organizers hope that it will be the first of many. As one scientist wrote about his own political awakening several years ago: