Why Philly has so many sinkholes
Sinkholes form when underground rock dissolves or sediment washes away and the surface collapses. Luis Diaz Devesa/Moment Collection/Getty…
The ozone hole above Antarctica will keep opening up each spring for decades to come – here’s why that still matters
NASA via Getty Images Laura Revell, University of Canterbury; Dan Smale, National Institute of Water and Atmospheric Research,…