New Jersey Rocks On Longer Than We Thought

by Michele S. Byers, Executive Director, New Jersey Conservation Foundation

New Jersey rocks! And I’m not talking about Bruce Springsteen, Bon Jovi, the Smithereens or even the Fugees. I’m talking about the bedrock that forms the foundation of this state we’re in!

A recent study found that New Jersey’s rocks are older than previously thought. The new knowledge gives us ever more reason to protect and preserve the New Jersey Highlands.


Geologists have long known that the Highlands region spanning northern New Jersey and adjacent states formed about a billion years ago. This period is known as the “Grenville Orogeny,” when continental land masses collided and portions of the earth’s crust along eastern North America were pushed up to form mountains.

The Appalachians, as originally formed, probably would have rivaled today’s Rocky Mountains in height. But billions of years of weathering have eroded the loftier heights down to the gentler mountain ranges we know today. In the process their rugged “bones” were exposed – the jagged, rocky ridges of today’s Highlands.

To gain a deeper understanding of how geological forces impacted the formation of the region, the N.J. Geological Survey and the U.S. Geological Survey embarked on a private grant-funded project to pinpoint the age of our ancient Highlands rocks.

Geologists selected a comprehensive cross-section of rocks from the region and shipped them to the Australian National University for analysis. A state-of-the-art method called Sensitive High-Resolution Ion Microprobe (SHRIMP) determined the age of the samples. The technique uses an intense beam of energy to measure the half-life of radioactive isotopes in zircon particles that contain lead and uranium.

The U.S. Geological Survey considers SHRIMP the most advanced method currently known for figuring out the precise age of ancient rocks formed through high temperature and pressure, such as those in the Highlands. The technology can date rocks to within nine million years of certainty.

Most of the rocks, it turns out, are significantly older than we originally thought. Most are between 1.02 billion to 1.25 billion years old, rather than the ballpark 1 billion years usually ascribed to the region’s rocks. In fact, one narrow stretch of rock spanning Wanaque and Ringwood in Passaic County was found to contain the oldest rocks in the state, at 1.37 billion years old. That’s 350 million years older than previously known, and it puts New Jersey’s rocks on par with those found in the Adirondacks and parts of southeastern Canada.

If you’re wondering how long ago that was, consider that it’s been only 65 million years since the age of dinosaurs and 200 million years since continental drift opened up the Atlantic Ocean.

But why does a difference of a few hundred million years matter? One reason is that potassium-rich granites of a certain age in the Highlands are likely to produce higher radon levels due to their higher than normal amount of radioactive elements. Knowing more about the rocks under our feet helps us make better environmental risk assessments.

Dating rocks also reminds us that beautiful and complex ecosystems like the Highlands take millennia to produce. Are we really willing to squander, in a matter of decades, something that took billions of years to form? If we do, no amount of human effort will be able to recover the Highlands’ drinking water, habitat or scenic vistas in a few decades, or even a few centuries.

Rock on, New Jersey. Rock on.

If you would like more information about conserving New Jersey’s precious land and natural resources, I hope you will consult New Jersey Conservation Foundation’s website at or contact me at

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