
https://knowablemagazine.org/content/art...erica-form
INTRO (excerpts): Connecticut — along with much of the rest of eastern North America — holds important clues about Earth’s history. This region, which geologists call the eastern North American margin, essentially spans the US eastern seaboard and a little farther north into Atlantic Canada. It was created over hundreds of millions of years as slivers of Earth’s crust collided and merged. Mountains rose, volcanoes erupted, and the Atlantic Ocean was born.
Much of this geological history has become apparent only in the past decade or so [...] The work could help scientists better understand the edges of continents in other parts of the world...
“The story that it tells about Earth history and about this set of Earth processes … [is] really fundamental to how the Earth system works,” says Maureen D. Long, who wrote an in-depth look at the geology of eastern North America for the 2024 Annual Review of Earth and Planetary Sciences.
The bulk of North America today is made of several different parts. To the west are relatively young and mighty mountain ranges like the Sierra Nevada and the Rockies. In the middle is the ancient heart of the continent, the oldest and stablest rocks around. And in the east is the long coastal stretch of the eastern North American margin. Each of these has its own geological history, but it is the story of the eastern bit that has recently come into sharper focus.
For decades, geologists have understood the broad picture of how eastern North America came to be. [...] Plate tectonics created and then broke apart an ancient supercontinent known as Rodinia. By around 550 million years ago, a fragment of Rodinia had shuffled south of the equator, where it lay quietly for tens of millions of years. That fragment is the heart of what we know today as eastern North America.
Then, around 500 million years ago, tectonic forces started bringing fragments of other landmasses toward the future eastern North America. Carried along like parts on an assembly line, these continental slivers crashed into it, one after another. The slivers glommed together and built up the continental margin.
During that process, as more and more continental collisions crumpled eastern North America and thrust its agglomerated slivers into the sky, the Appalachian Mountains were born. To the west, the eastern North American margin had merged with ancient rocks that today make up the heart of the continent, west of the Appalachians and through the Midwest and into the Great Plains.
By around 270 million years ago, that action was done, and all the world’s landmasses had merged into a second single supercontinent, Pangaea. Then, around 200 million years ago, Pangaea began splitting apart, a geological breakup that formed the Atlantic Ocean, and eastern North America shuffled toward its current position on the globe.
Since then, erosion has worn down the peaks of the once-mighty Appalachians, and eastern North America has settled into a mostly quiet existence. It is what geologists call a “passive margin,” because although it is the edge of a continent, it is not the edge of a tectonic plate anymore: That lies thousands of miles out to the east, in the middle of the Atlantic Ocean.
In many parts of the world, passive continental margins are just that — passive, and pretty geologically boring... [...] But eastern North America is different. There’s so much going on there that some geologists have humorously dubbed it a “passive-aggressive margin.”
[...] That action includes relatively high mountains — for some reason, the Appalachians haven’t been entirely eroded away even after tens to hundreds of millions of years — as well as small volcanoes and earthquakes. Recent east-coast quakes include the magnitude-5.8 tremor near Mineral, Virginia, in 2011, and a magnitude-3.8 blip off the coast of Maine in January 2025. So geological activity exists in eastern North America. “It’s just not following your typical tectonic activity,” says Sarah Mazza, a petrologist at Smith College in Northampton, Massachusetts... (MORE - details)
INTRO (excerpts): Connecticut — along with much of the rest of eastern North America — holds important clues about Earth’s history. This region, which geologists call the eastern North American margin, essentially spans the US eastern seaboard and a little farther north into Atlantic Canada. It was created over hundreds of millions of years as slivers of Earth’s crust collided and merged. Mountains rose, volcanoes erupted, and the Atlantic Ocean was born.
Much of this geological history has become apparent only in the past decade or so [...] The work could help scientists better understand the edges of continents in other parts of the world...
“The story that it tells about Earth history and about this set of Earth processes … [is] really fundamental to how the Earth system works,” says Maureen D. Long, who wrote an in-depth look at the geology of eastern North America for the 2024 Annual Review of Earth and Planetary Sciences.
The bulk of North America today is made of several different parts. To the west are relatively young and mighty mountain ranges like the Sierra Nevada and the Rockies. In the middle is the ancient heart of the continent, the oldest and stablest rocks around. And in the east is the long coastal stretch of the eastern North American margin. Each of these has its own geological history, but it is the story of the eastern bit that has recently come into sharper focus.
For decades, geologists have understood the broad picture of how eastern North America came to be. [...] Plate tectonics created and then broke apart an ancient supercontinent known as Rodinia. By around 550 million years ago, a fragment of Rodinia had shuffled south of the equator, where it lay quietly for tens of millions of years. That fragment is the heart of what we know today as eastern North America.
Then, around 500 million years ago, tectonic forces started bringing fragments of other landmasses toward the future eastern North America. Carried along like parts on an assembly line, these continental slivers crashed into it, one after another. The slivers glommed together and built up the continental margin.
During that process, as more and more continental collisions crumpled eastern North America and thrust its agglomerated slivers into the sky, the Appalachian Mountains were born. To the west, the eastern North American margin had merged with ancient rocks that today make up the heart of the continent, west of the Appalachians and through the Midwest and into the Great Plains.
By around 270 million years ago, that action was done, and all the world’s landmasses had merged into a second single supercontinent, Pangaea. Then, around 200 million years ago, Pangaea began splitting apart, a geological breakup that formed the Atlantic Ocean, and eastern North America shuffled toward its current position on the globe.
Since then, erosion has worn down the peaks of the once-mighty Appalachians, and eastern North America has settled into a mostly quiet existence. It is what geologists call a “passive margin,” because although it is the edge of a continent, it is not the edge of a tectonic plate anymore: That lies thousands of miles out to the east, in the middle of the Atlantic Ocean.
In many parts of the world, passive continental margins are just that — passive, and pretty geologically boring... [...] But eastern North America is different. There’s so much going on there that some geologists have humorously dubbed it a “passive-aggressive margin.”
[...] That action includes relatively high mountains — for some reason, the Appalachians haven’t been entirely eroded away even after tens to hundreds of millions of years — as well as small volcanoes and earthquakes. Recent east-coast quakes include the magnitude-5.8 tremor near Mineral, Virginia, in 2011, and a magnitude-3.8 blip off the coast of Maine in January 2025. So geological activity exists in eastern North America. “It’s just not following your typical tectonic activity,” says Sarah Mazza, a petrologist at Smith College in Northampton, Massachusetts... (MORE - details)