A team of researchers has confirmed that a rock formation in Michigan, the Watersmeet Gneiss, holds the title of America’s Oldest Rock, with an estimated age of at least 3.6 billion years.
A rock formation in Michigan has been crowned the oldest known rock in the United States, with an estimated age of at least 3.6 billion years.
For decades, a sign in Minnesota proudly proclaimed itself as the ‘World’s Oldest Rock,’ boasting an age of 3.8 billion years. However, this title has been disputed by geologists who argue that it may be overstated by at least 300 million years.
The search for America’s oldest rock is not just an exercise in trivia; it raises fundamental questions about how we reconstruct Earth’s history. Without precise ages, scientists can’t pinpoint when life began, mountains grew or climates shifted.
Earth is estimated to have formed approximately 4.54 billion years ago from the gravitational collapse of a giant cloud of gas and dust called a solar nebula.
Over time, this material cooled and condensed into the rocky planets, including Earth.
The planet's surface has undergone significant changes due to geological processes such as plate tectonics and volcanic activity.
Fossil records indicate that life emerged on Earth at least 3.5 billion years ago, with complex life forms developing around 541 million years ago during the Cambrian explosion.
When geologists date rocks, they’re really dating minerals. ‘A rock can be composed of minerals that formed at different ages,’ says Carol Frost, a geologist who specializes in dating ancient rocks. It’s like trying to date a building by analyzing its bricks, which aren’t necessarily the same age.
The mineral zircon is a fan favorite, but its durability means it often outlasts its host rock. After crystallizing in magma, zircons can be swept into sediments or crushed by tectonic forces, processes that form new rocks but may distort the crystal’s age.
Zircon is a rare mineral composed of zirconium silicate (ZrSiO4).
It is one of the oldest minerals on Earth, with some crystals estimated to be over 4.4 billion years old.
Zircon is often found in igneous and metamorphic rocks and is prized for its distinct crystal structure and ability to preserve ancient information about the Earth's history.
Its hardness makes it resistant to weathering, allowing it to remain intact for billions of years.
In addition to its scientific value, zircon is also used as a gemstone due to its unique properties.
The disputed champion, Minnesota‘s Morton Gneiss, contains zircons dating to 2.6 billion, 3.3 billion and 3.5 billion years ago. ‘There may have been two rocks of different ages that became mixed at a third youngest time,’ Frost says.
Most zircons in Wyoming‘s Sacawee Gneiss date to 3.4 billion years ago, though nine rogue grains date to 3.8 billion years ago. Michigan‘s Watersmeet Gneiss, on the other hand, has a wild age range of 3.8 billion to 1.3 billion years old.
The team settled on a minimum age of 3.6 billion years for the Watersmeet Gneiss, handing it the title of ‘America’s Oldest Rock’ – for now. This discovery highlights the importance of precise ages in reconstructing Earth’s history.
Vervoort isn’t worried that this study will upend geologic history, explaining that younger rocks are usually much easier to date. Early Earth is another matter. ‘When I give talks on the early Earth, I always finish with the Salvador Dali painting with the drooping clocks in a barren landscape,’ he says.
The sign proclaiming a gneiss in Minnesota as the ‘World’s Oldest Rock’ should be uprooted and revised to ‘America’s Oldest Rock.’ Researchers argue that this will give us a more accurate understanding of our planet’s history.
