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Picture the Chesapeake Bay. You are seeing crabs, sailboats, a long low bridge, maybe a paper tray of something fried near the water. Hold that picture.
Discover why the Chesapeake Bay is actually a drowned river valley and the largest estuary in the US, with unique geography and history.
Ask about this video. Answers come from its transcript only — with the timestamp, so you can check them.
Generated from the transcript and can be wrong — check the timestamp.
Key Takeaways
- The Chesapeake Bay is a drowned river valley estuary, not a typical ocean bay.
- Its shallow depth and vast watershed make it highly sensitive to environmental changes.
- Historic oyster populations played a crucial role in water filtration and ecosystem health.
- Human activities and natural processes have drastically altered the bay’s ecology and geography.
- Understanding the bay’s true nature helps explain its unique environmental challenges and history.
What the video covers
- The Chesapeake Bay is not a traditional bay but a drowned river valley formed by the Susquehanna River cutting a canyon.
- It has 11,684 miles of shoreline, more than the entire US west coast, due to its many drowned side valleys and creeks.
- The bay is shallow, averaging about 21 feet deep, with large areas where a person could wade without submerging their head.
- The Chesapeake Bay is the largest estuary in the United States, where freshwater mixes with seawater.
- The bay’s watershed spans 64,000 square miles across six states and DC, impacting over 18.5 million people.
- Historically, the bay produced half of the world's oyster supply, which supported local economies and even led to armed conflicts known as the Oyster Wars.
- Oyster reefs acted as a natural filtration system, cleaning the entire bay every 3-4 days, but today oyster populations are under 1% of historic levels.
- The bay’s geography and ecology are shaped by its shallow depth, extensive watershed, and geological history including an ancient asteroid impact crater.
- Sea level rise and land subsidence threaten islands and communities within the bay, with some islands lost entirely over the past 150 years.
- Despite its importance, many people only experience the bay from crossings like the Chesapeake Bay Bridge, unaware of the complex underwater landscape.
Chapters
- 00:00Introduction and Misconceptions about Chesapeake Bay
- 00:41Shallow Depth and Unique Geography
- 01:25Definition and Formation of the Bay
- 02:05Chesapeake Bay Bridge and Hidden River Channel
- 02:46Complex Shoreline and Side Valleys
- 03:40Physical Characteristics and Water Dynamics
- 04:42Watershed and Human Impact
- 05:34Historical Oyster Industry and Oyster Wars
- 08:09Oyster Population Decline and Environmental Impact
- 09:58Geological History and Environmental Challenges
Full Transcript — Download SRT & Markdown
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The shape of it is right, and almost everything underneath it is wrong. This is not a bay.
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Not in the way you mean the word. It is a river valley that drowned.
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The Susquehanna cut a canyon through what is now Maryland and Virginia, the sea came up and filled it, and what you are looking at is the top of that canyon with water sitting in it.
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It has 11,684 miles of shoreline. That is more edge than the entire west coast of the United States. And it is shallow.
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Not shallow the way an ocean shelf is shallow, but shallow like a wading pool.
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Average depth is about 21 feet, and a 6-foot adult could wade across more than 700,000 acres of it without wetting the brim of a hat.
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So why does everyone call it a bay? Thirty facts, counting down, and the last one is what is under there.
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Number 30. Nobody was paying attention to what the word meant. A bay is an inlet of the sea, a bite taken out of a coastline, water pushing into land.
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The Chesapeake is the opposite shape. It is a valley that the sea moved into, which makes it an estuary rather than a bay, and it is the largest estuary in the United States. That sounds like pedantry for about ten seconds, until you
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understand that every strange thing about this place follows from it. A bay is a piece of ocean.
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An estuary is a piece of drowned country. You are not looking at the sea.
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You are looking at land with the sea on top of it. Number 29. You have already been on top of it.
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The Chesapeake Bay Bridge opened in 1952 and runs about 4 miles from shore to shore near Annapolis, and for a great many drivers, that crossing is the entire relationship with this body of water.
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4 miles of steel, a view out the passenger window, and back to the radio.
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Somewhere under the middle of those spans is the old river channel, the deepest cut of the drowned canyon, and nothing on the bridge tells you it is there.
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The water beneath those cars is doing something none of the drivers can see. Number twenty-eight.
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Start with the edge, because the edge is the first number that stops making sense.
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11,684 miles of shoreline reads like a typo for a body of water you can drive around in a single day. It is not a typo.
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That number is enormous because a drowned valley comes with drowned side valleys, and each side valley has its own drowned creeks, and each creek has drowned fingers off it.
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The coastline keeps folding into itself at smaller and smaller scales. Every river that fed the Susquehanna is now an arm of the Chesapeake.
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Number 27. The surface covers about four thousand four hundred and eighty square miles, and the proportions are stranger than the area.
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At its widest, near the mouth of the Potomac, this thing spans about 35 miles.
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At its narrowest, up near Aberdeen, Maryland, it pinches to 3.4. Where it meets the Atlantic, the opening is only about 12 miles across. So a body of water 200 miles long meets the open ocean through a gap 12 miles wide, which is why what
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goes into the Chesapeake tends to stay in the Chesapeake. Number 26. Which brings us back to that 21-foot average, and to the 700,000 acres a tall adult could stand up in.
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Consider what that means in physical terms. There is not much water here, spread across an enormous floor, and a thin layer of water does everything faster than a deep one. Spring warms it fast.
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It freezes at the edges in a hard winter. It responds to every drop of rain, every load of sediment, and every ounce of fertilizer that runs off the land around it.
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Shallowness is not a trivia fact about the Chesapeake. Shallowness is the reason it behaves the way it does.
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Number 25. And a great deal runs into it. The watershed covers 64,000 square miles across six states and the District of Columbia, reaching from upstate New York down through Pennsylvania, Delaware, Maryland, Virginia and West Virginia, and it holds more than
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18.5 million people. If you live in Harrisburg, or Richmond, or a suburb of Washington, or a farm town in upstate New York, your gutter is plumbed into the Chesapeake Bay whether you have ever seen it or not.
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It is not how those people tend to describe where they live. By the water, every one of them does.
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And everything they send downhill ends up in the same place, which happens to be the one part of this bay that is not shallow at all. Number twenty-four.
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There is one genuine hole in the floor. Southeast of Annapolis, the bottom drops away to about one hundred and seventy-four feet in a spot the charts call The Hole.
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It is a scour pit gouged into the old river channel, which is to say it is a surviving piece of the canyon, a place where the current kept the sediment from filling things in.
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Everywhere else, the drowned valley has been buried under thousands of years of mud. Down there, the shape of the original river is still open.
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Number 23. That canyon was cut by a river that starts nowhere near the ocean.
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The Susquehanna rises at Cooperstown, New York, runs more than 440 miles south through Pennsylvania and Maryland, reaches salt water at Havre de Grace, and supplies about half of all the fresh water the bay receives.
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Half. From one river, out of a state that does not touch the Chesapeake. In the most literal sense available, this bay is the mouth of a New York river, and the reason the water tastes fresher at the top than the bottom is that the Susquehanna is still
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filling the valley it dug. Number 22. Now for what people did with all of it.
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In the 1880s, the Chesapeake produced close to half of the world's supply of oysters.
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Not half of America's supply. Half of the planet's. New England crews sailed south once they had stripped their own beds, and the bay filled with dredge boats working reefs that had been building since the valley flooded.
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That is the kind of number that reorganizes an entire coastline, and it did. Towns existed because of it.
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Railways were run to it. And it could not last. Number 21. It also started a war.
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From 1865 to 1959, the Chesapeake ran a low-grade shooting conflict over shellfish, remembered now as the Oyster Wars.
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Maryland began requiring harvest permits in 1865, and when that failed to hold, the state commissioned an armed force in 1868 to patrol the beds.
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An actual navy. For oysters. It was underfunded from the start and outnumbered by crews who dredged at night, came armed, and were willing to shoot back at a state patrol boat.
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Number 20. And that conflict kept killing people well inside living memory. The last man to die in the Oyster Wars was Berkeley Muse, shot in 1959 while dredging off Swan's Point.
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Sit with the date. Not the eighteen hundreds. 1959, the same year Jack Kilby filed the first patent for the integrated circuit, 94 years after the first permit law, and Americans were still shooting at each other on this water over shellfish.
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The conflict outlasted the oyster boom that started it by decades. Number 19. Here is the detail almost everyone misses about those oysters. They were never only food.
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A reef of live oysters is a filtration system, each animal pulling water through itself and dropping the sediment out, and the historic population of the Chesapeake could strain the entire volume of the bay in 3 to 4 days. The whole thing.
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Every drop of a 200 mile estuary, run through shellfish and cleaned, about twice a week.
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The water your grandparents described was not clearer because the era was gentler. It was clearer because something alive was doing the work.
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Number 18. Today the native oyster population sits at under 1% of historic levels, hit by two protozoan diseases on top of a century of overharvesting and pollution, and filtering the bay one time over would now take close to a year. Three days
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to a year. Three days to a year. That change happened underwater, on the bottom, where there was nothing for anyone to watch.
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The Chesapeake did not get murkier because something was added to it.
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If you grew up on this water and remember being able to see your own feet, that memory is a data point, and I would like to read it in the comments.
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Number 17. The bay also keeps things. At Mallows Bay, a shallow bend on the Potomac, sit the remains of more than 100 wooden steamships, packed in close along the shoreline.
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From the air they read as a fleet of long, narrow green islands, arranged in rows, because trees and marsh grass are growing out of the hulls.
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They have been sitting there for a century, and they are sitting there because of a deadline that nobody managed to meet.
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Number 16. Those ships were built for a war that ended first. The United States ordered them beginning in nineteen seventeen as an emergency fleet, hundreds of wooden hulls thrown together at speed because German submarines were sinking steel merchant ships faster than the yards could
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replace them. Wood was available. Steel was not. Construction ran through 1919, the yards worked flat out, and the armistice arrived before the fleet was ever needed.
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A national emergency programme delivered a fleet of brand new ships with no war left to carry anything to, and no peacetime buyer who wanted a wooden steamer.
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Number 15. So they were sold off, towed to a quiet bend in the river, and burned and scuttled for their scrap metal, with salvage crews picking over the engines and boilers on and off from the 1920s through the 1940s.
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Then everyone stopped caring, and the river took them. In 2019, the whole graveyard was designated the Mallows Bay Potomac River National Marine Sanctuary.
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A century after somebody wrote those hulls off as worthless, they are protected by federal law as a habitat and an archaeological site.
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Number 14. Other things the bay keeps, it keeps taking. Holland Island, out in the Maryland portion, once held a working village with houses, a store, a school, and a church, and a community of watermen who fished and dredged off it.
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Erosion worked at the western shore for a century, storms took bites out of what remained, and families dismantled their own houses and barged them to the mainland.
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In 2010, the last standing house on Holland Island collapsed into the water. The island is now a low scatter of marsh that goes under at high tide.
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Number 13. Poplar Island tells the same story with sharper numbers attached. In 1847, it covered more than one thousand acres, enough for farms, a school, and a village.
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By 1996, the same island was down to under four acres, broken into a few scraps of remnant marsh.
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That is a loss of more than 99% of a place inside 150 years, and there was no single dramatic event behind it.
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Wind, waves, storms, and a rising waterline took it apart. Number 12. And then people did something unusual about it.
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Beginning in 1998, engineers started building containment dikes in the shape of the island that used to be there, and filling them with mud dredged out of the Baltimore shipping channels and barged about twenty five miles down the bay.
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Poplar Island is being rebuilt from the sediment scraped off the bottom of its own estuary.
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The first phase enclosed 640 acres. Wildlife is nesting on ground that did not exist in the 1990s, built out of material that used to be in the way of container ships.
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Number 11. Storms take their share of these islands, but weather is not the whole account. The Chesapeake sits inside a hot spot for relative sea level rise, and the Tangier Islands sit close to the middle of it.
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Water is arriving here faster than almost anywhere else on the Atlantic coast of the United States, and the low marsh islands feel it first because they have no elevation to spare.
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A place that stands 2 feet above the waterline does not need a catastrophe. It needs a slow trend and enough decades.
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Number 10. Put a figure on it. Sea level in this region is rising at about three and a half millimetres a year, and the Chesapeake carries the highest rates of sea level rise anywhere on the American Atlantic seaboard.
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Which raises a question that seems to answer itself, and does not. Everyone assumes a rising waterline means a rising ocean.
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Here, the ocean is only half the story, and the other half is the part that gets left out of every article written about this place. Number nine.
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About half of that rise is not the water coming up. It is the ground going down.
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Number 8. Some of that sinking is our own doing. Pumping groundwater out of the aquifers beneath this region has compacted them at something in the range of one and a half to 3.5 mm a year, and by the
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reckoning of the United States Geological Survey, that compaction accounts for more than half of the land subsidence measured across the southern Chesapeake.
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Take the water out of a layer of sediment, and the layer settles, the way a sponge collapses when you squeeze it.
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Hampton Roads is sinking in part because it has been drained from underneath. Number 7. The rest of the sinking is a glacier that never arrived.
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During the last ice age, the great North American ice sheet stopped well north of the Chesapeake.
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No ice ever sat on this ground. Nothing here was scraped, gouged or buried, and for a long time that was taken to mean the region had no glacial story of its own. That turned out to be backwards.
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Number 6. Ice that heavy pushes down on the crust beneath it, and the rock displaced underneath has to go somewhere, so it flows sideways and lifts the land around the edge of the ice sheet into a broad rise.
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Geologists call it a forebulge. The Chesapeake region sat on that raised rim for thousands of years, held up by ice hundreds of miles away that it never touched.
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When the ice melted about 10,000 years ago, the pressure came off, the rock began flowing back, and the bulge started deflating. It is still deflating today.
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This bay is sinking into a hollow left by a glacier that stopped a few hundred miles short of it.
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Number 5. Estimates put the extra drop from that collapse at up to about half a foot over the next hundred years.
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Measure that against the rest of the list. On a body of water averaging 21 feet deep, with 700,000 acres shallow enough to stand up in and marsh islands sitting a foot or two above the tide, six inches of settling is not a rounding error.
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It is the difference between an island and a shoal, and Holland Island is what that difference looks like when it finishes.
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Number 4. So how old is any of this? Geologists cored the floor of the bay in 1999 and again in 2003, pulled up the layers, and read them like tree rings.
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18,000 years ago, this whole region was dry land, with sea level more than 400 feet below where it stands now and the coastline far out on the continental shelf.
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As the ice sheets melted, the ocean climbed and pushed up the river valleys. Those cores date the modern chesapeake to somewhere between 9,500 and 8,000 years old.
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Number 3. And it only took the outline you would recognise on a map about 3,000 years ago.
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This part almost never makes the tour. In its current shape, this bay is younger than the pyramids at Giza.
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It is younger than Stonehenge. Older than every human structure you could name is the ground underneath it, and the reason that matters is that everything on this list has been sitting on top of something much older.
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In 1983, somebody pulled a piece of it up. Number 2. That year, a drill core came back holding a 10 cm layer of shattered debris from the late Eocene, material that had been thrown, not deposited.
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A United States Geological Survey team led by C Wylie Poag worked out what it was, and then spent years assembling an international effort to map the thing it had come from.
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People believed they had the full picture of this coastline. They were wrong by a margin that is difficult to overstate.
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Number 1. About 35 million years ago, an object about two miles across came in over the shallow Atlantic shelf at something like 12 miles per second and struck what is now the lower Chesapeake Bay.
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It left a buried structure about 56 miles wide, the largest impact crater in the United States and one of the largest anywhere on Earth, and it is still down there, sealed under the water and the sediment and invisible from the surface.
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In 2005, a drilling team bored into the middle of it, more than a mile straight down, to find out what the impact had trapped. What they found was water.
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More than half a mile below the bay floor, filling the shattered rock, sat seawater from the Early Cretaceous, somewhere between one hundred and one hundred forty-five million years old, about twice as salty as the ocean above it.
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The team that dated it, led by Ward Sanford of the Geological Survey, published the result in the journal Nature in 2013. It is the oldest large body of seawater ever identified anywhere on the planet, older than the Atlantic in its
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modern form, sealed in place by an asteroid and sitting undisturbed ever since. So the next time you cross that bridge, understand what is stacked underneath the car.
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A river canyon that drowned. Sitting inside a crater punched out by an asteroid. Holding a sea that was already ancient when the impact sealed it in. There is no sign for any of it, nobody tells you, and the
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whole stack takes about four minutes to drive over.
Topics:Chesapeake Bayestuarydrowned river valleySusquehanna Riveroystersoyster warswatershedshorelinebay ecologysea level rise
