Tough crystals hit by cosmic rays act as clocks to date ancient landscapes

Zircon crystals are among the toughest minerals on Earth, capable of surviving billions of years of tectonic recycling. When these crystals sit near the Earth's surface, they are bombarded by cosmic rays that cause uranium decay, trapping helium atoms inside their structure. By measuring this trapped helium, scientists can determine exactly when a landscape was first exposed to the sky, creating a precise geological clock.