Contents

03 July 2020
Vol 369, Issue 6499

About The Cover

Cover image expansion

COVER Tinged blue with minerals, La Poza Azul II is one of hundreds of spring-fed pools in Cuatro Ciénegas, an oasis in the desert of northern Mexico that preserves a vast diversity of microbes resembling those in ancient oceans. Drainage for agriculture threatens the unique ecosystems of this oasis. See page 20.
Photo: Miguel Angel de la Cueva