The Secret of America's Oldest Rock

In a new study published in GSA Today, the oldest rock in the United States is the Watersmeet gneiss in Michigan, which dates back at least 3.6 billion years.

For decades, a plaque erected in 1975 has stood proudly in the Minnesota River Valley that reads " World's Oldest Rock ." The plaque marks the location of a gneiss believed to be 3.8 billion years old.

However, recent research by a team of experts led by geologist Carol Frost has demonstrated that the above figure may have been exaggerated by at least 300 million years.

The story began with a conversation among geologists. Co-authors of the study, Professor Bob Stern of the University of Texas at Dallas, and graduate student Clinton Crowley initiated the discussion. They then contacted experts in ancient rock dating, including geologist Frost, to help unravel the mystery of the rock.

The team sampled gneiss from three areas: Minnesota,

Determining the age of rocks is not easy. When experts age rocks, they are actually dating the minerals that make up the rock, says Frost, a geologist at the University of Wyoming. It’s like trying to age a building by analyzing each brick, but not all the bricks are the same age.

The mineral zircon is often used by scientists to date rocks. However, its durability – its ability to withstand weathering, high temperatures and pressures – means it often outlives its host rock. After crystallizing in magma, zircon crystals can be swept into sediments or crushed by tectonic forces, forming new rocks but potentially distorting the age of the crystals.

The team took gneiss samples from three locations: Minnesota, Wyoming, and Michigan. The analysis showed that the Watersmeet gneiss in Michigan had zircon ages ranging from 3.8 billion to 1.3 billion years old. The rock showed signs of a turbulent past: volcanic intrusion, metamorphism, and tectonic activity. Based on the evidence collected, the scientists determined its minimum age to be 3.6 billion years old.

Jeffrey Vervoort, a geologist at Washington State University who was not involved in the study, said understanding the exact age of ancient rocks helps scientists reconstruct Earth's history more accurately, from the time life began to the rise of mountains and climate change.

Although the Watersmeet gneiss currently holds the title of "Oldest Rock in America," scientists believe that even older rocks may exist.

Readers are invited to watch the video : The mystery of the hundred-ton rock that challenges all laws of physics.

Source: https://khoahocdoisong.vn/bi-mat-tang-da-lau-doi-nhat-nuoc-my-post269691.html