A New Age

About 4,200 years ago, a 200-year-long megadrought led to the downfall of human civilizations. Ancient populations were forced to travel long distances in search of water. Recently, evidence of the disaster’s impact was discovered hidden within rocks formed all those years ago. The finding led geologists to declare that we are now living in a new geological age—the smallest unit of geological time—called the Meghalayan (meg-huh-LI-yan) age.

During Earth’s 4.6-billion-year history, the planet’s surface has undergone a huge transformation from its beginnings as a lifeless ball of molten rock to today. Changes in climate, volcanic activity, and shifting tectonic plates—giant rock slabs that make up Earth’s crust—have all had enormous impacts on the planet. Geologists classify these phases in Earth’s evolution using different units of geological time (see Geological Time Scale).

About 4,200 years ago, a megadrought led to the downfall of human civilizations. It lasted 200 years. Groups of people had to travel long distances to find water. Recently, researchers found signs of the disaster’s effects. This evidence was hidden in rocks formed way back then. Because of what they found, geologists say that now we are living in a new geological age. That’s the smallest unit of geological time. This one is called the Meghalayan (meg-huh-LI-yan) age.

Earth’s surface has undergone major changes during the planet’s 4.6-billion-year history. Earth started as a lifeless ball of molten rock. Changes in climate and volcanic activity have had huge effects on the planet. So have shifting tectonic plates. These giant rock slabs make up Earth’s crust. Geologists label these periods in Earth’s development using different units of geological time (see Geological Time Scale).

To define a unit of geological time, scientists study the chemical makeup of rocks and the fossils they contain. That allows researchers to date the rocks and understand the conditions on Earth during their formation. “Every kind of rock is a record of an event from the past,” explains Stan Finney, a geologist involved in approving geological units of time for the International Union of Geological Sciences.

In the case of the new Meghalayan age, researchers analyzed a rock formation called a stalagmite growing on the ground of a cave in the northeastern state of Meghalaya, India. They found oxygen (O) isotopes, or different types of an element, that indicated the rock formed during a period of long drought. Geologists around the globe eventually made the same observations within rock and ice samples from all seven continents. That confirmed the initial findings, providing proof of the new age.

Scientists study the chemical makeup of rocks to define a unit of geological time. They also study the fossils in the rocks. That tells researchers about the age of the rocks, plus the conditions on Earth when they formed. “Every kind of rock is a record of an event from the past,” explains geologist Stan Finney. He’s involved in approving geological units of time for the International Union of Geological Sciences.

With the new Meghalayan age, researchers studied a rock formation called a stalagmite. It was growing on the ground of a cave in northeastern India in the state of Meghalaya. They found oxygen (O) isotopes, or different types of an element. The isotopes showed that the rock formed during a long drought. Over time, geologists around the globe found the same thing. They saw evidence in rock and ice samples from all seven continents. That backed up the first findings, giving proof of the new age.