Rocks older than 4 billion years are not available to study, making the first 500 million years of Earth's history particularly mysterious. But cutting-edge techniques are now allowing geologists to study survivors of Earth's early era.

In 1912, Viktor Hess took to the sky in a hot-air balloon and discovered a radioactive energy now called “cosmic rays.” Travel to Argentina to see how scientists now hope to discover at long last where the highest-energy cosmic rays are coming from.

By unearthing sediment deposits tsunamis leave behind, scientists can study the waves' origins, extent, and frequency — and identify locations that have the geological apparatus to produce a tsunami, but haven't in written history.

A tsunami hasn't affected the Pacific Northwest coast since 1964, yet bright-blue metal signs warning of them dot coastal streets. Find out why scientists are certain these communities are at risk.

Why did Hawaiian officials evacuate Hilo Bay in 1986 after a 7.7 earthquake but call off an evacuation in 2003 after a 7.8 one? The answer is DART. Learn more.

During a July 2004 project to drill an ice core from the top of Peru's Andes Mountain, the lead researcher took a detour… and made a discovery with profound implications. Learn more.

By analyzing the relics glaciers hold — compacted snow and trapped air from ancient atmospheres, ash from long-quiet volcanoes, dust, insects, and pollen — scientists can reconstruct hundreds of thousands of years of Earth’s climate.

In the past two million years alone, Earth has experienced around 20 ice ages — cycles of advance and retreat of large continental ice sheets. When is the next one due? And will global warming change that due date?

Climate change isn’t always slow, small, and imperceptible in a human lifetime. Ice core analysis has found a single decade in which temperatures over Greenland shot up about 15 degrees Celsius.

Scientists know that the unusual and rapid temperature jump of the Younger Dryas was felt over half the globe. But they're only now beginning to understand why.