Scientists exploring an ancient impact crater deep below the mouth of the Chesapeake made an unexpected discovery recently: a sea that is between 100-150 million years old. The discovery will help researchers understand what shaped our continent long ago, and perhaps most exciting, to study a period that could offer clues about the effects of climate change. We explore the ancient sea with one of the lead scientists on the project.


  • Ward Sanford Hydrologist, US Geological Survey
  • David Nelms Groundwater specialist for Virginia, US Geological Society

Simulation Of Ancient Chesapeake Bay Impact Crater

This computer simulation illustrates how an asteroid contributed to the formation of the Chesapeake Bay impact crater. Light brown symbolizes sediment and water, while the gray color symbolizes hard rock. *Note: there is no audio in this video. (Credit/Gareth S. Collins and Kai Wünnemann/Geology)


  • 12:28:02

    MR. KOJO NNAMDIRecently scientists exploring an ancient crater caused by the impact of a giant asteroid made an unexpected discovery deep below the mouth of the Chesapeake Bay. They found a body of water that is between 100 and 150 million years old, the oldest sea yet discovered anywhere. It's a discovery that will help researchers understand what our continent and the water around it looked like long ago. And what may be most exciting for some, the water allows scientists to study a period that could give us clues about the effects of future climate change.

  • 12:28:38

    MR. KOJO NNAMDIJoining us to talk about this is Ward Sanford. He is a hydrologist with the U.S. Geological Survey. He's the lead scientist studying the hydrology of the Chesapeake Bay impact crater. Ward Sanford, thank you for joining us.

  • 12:28:52

    MR. WARD SANFORDThank you, Kojo, for having me.

  • 12:28:53

    NNAMDIJoining us by phone from Richmond is David Nelms. He is a groundwater specialist for Virginia with the U.S. Geological Survey. David Nelms, thank you for joining us.

  • 12:29:01

    MR. DAVID NELMSGlad to be here, Kojo. Thank you.

  • 12:29:04

    NNAMDIWe're inviting you too to join the conversation at 800-433-8850. Ward Sanford, this is an amazing find. It's the oldest large body of seawater in the world but you were not looking for an ancient sea originally. What the heck were you doing?

  • 12:29:19

    SANFORDWell, that's a good question. I can put this in a little bit of context. In the USGS we collect scientific information of many different kinds to help society manage its resources and hazards. And so in this case we were helping investigate the water resources of southeastern Virginia. So the project was really looking at the aquifer down there where a lot of people depend on its groundwater. And there was a discovery that a very large impact crater had disrupted this aquifer. So we had the opportunity to -- along with the International Continental Drilling Program to do a very deep core hole into the crater.

  • 12:30:07

    SANFORDAnd one of the things we were investigating, which we had discovered beforehand, was that some of the water down there in the aquifer was saltier than seawater. So we wanted to answer -- or look for an answer to that question, what was the origin of the salinity. And so by -- I was in charge of taking samples of cores as we cored in looking at the concentrations of the salt and the water. And so what we ended up discovering was in fact this water was not recent -- even from the recent ocean but it had been in the ground for more than 100 million years, since the time of the early cretaceous, so the time of the dinosaurs.

  • 12:30:51

    NNAMDISo the clue that indicated to you that this might be the case was the salinity of the water.

  • 12:30:58

    SANFORDA little bit. What -- there were several pieces of evidence that came together. The concentrations of some of the elements gave us a fingerprint that looked like ocean water. One of the important things was looking at the helium in the water because helium in the ground accumulates very slowly from the decay of uranium. There's not a lot of uranium in the ground but there's enough that helium accumulates overtime. And so we had also done another recent study where we were able to determine how fast this helium accumulates in the coastal aquifers.

  • 12:31:36

    SANFORDAnd then when we compare the helium concentrations in the aquifers normally to what was in the crater, the crater helium was extremely high. And we were able to use that to date this water back to 100 to 150 million years. But then we looked at the arrangement of the continents in the North Atlantic Ocean at that time we realized it would've been not unusual that that water was much higher in salinity at that time.

  • 12:32:02

    NNAMDIDavid, water that's at least 100 million years old, this is something I guess a lot of us are curious about. We know that you can date objects, David, but how do you date water?

  • 12:32:14

    NELMSWell, Ward's kind of described one method, helium. There's other methods, carbon 14. You've heard of people using that to date, like, artifacts and wood. There's chlorine 36 which is an isotope that you can date water with. And then our researchers in Reston that worked for Ford have developed techniques to look at waters that are say less than 60 years old. And they use things like Freon that has accumulated in the atmosphere. They use an isotope of hydrogen called tritium which is a remnant of the above-ground nuclear testing back in the '60s and '70s.

  • 12:33:05

    NNAMDIWe're talking with David Nelms. He is a groundwater specialist for Virginia with the U.S. Geological Survey. Ward Sanford is a hydrologist with the U.S. Geological Survey. He's the lead scientist studying the hydrology of the Chesapeake Bay impact crater. And we're talking about the impact that that study is having on what we understand about climate. And we're inviting your calls at 800-433-8850. What do you think about the discovery of an ancient sea under the Chesapeake? You can send email to or send us a Tweet at kojoshow.

  • 12:33:38

    NNAMDIDavid Nelms, it's amazing to think that this ancient seawater is likely more than 100 million years old but your work involves managing the groundwater in our region. And this came as a surprise to all of us here, but the groundwater in our area, the aquifers used by cities and industry needing fresh water contains water that can also be quite old. It's not unusual, it's my understanding, for our water sources to be a million or more years old. Is that right?

  • 12:34:09

    NELMSYeah, well, it all depends. It depends on where you are. Some recent work by another colleague of ours up in Reston, Neil Plummer in Maryland, he dated waters out to 2, 3 million years. In Virginia we've used carbon 14 and we've gotten ages in the tens of thousands of years. And that's what was so kind of telling. Some work by Randy McFarland here in Richmond, the Potomac Aquifer, which is the one that Ward was talking about was disrupted, is -- tends to be sandier in Virginia than it is up in -- to the north in Maryland and to the south in North Carolina. And our ages, although they're old, they're actually much younger than what people -- what Neal and them found up in Maryland.

  • 12:35:12

    NELMSAnd so then when we get to the impact crater it's really a dramatic change from tens of thousands of year old water to a million -- at least a million, 2 million to what Ward and them have found.

  • 12:35:28

    NNAMDIAnd they're talking about 100, 150 million possibly. Ward, if I understand it, this ancient sea has been trapped there deep underground for 100 plus million years. What do scientists think the Atlantic ocean looked like at the time?

  • 12:35:45

    SANFORDSo, right. It looked very different than it does today. Most people don't -- aren't aware of how this came about. But actually the North Atlantic is much older than the South Atlantic. The North Atlantic probably split open maybe 180 million years ago and continued to widen. So during the time when this water was being trapped in the sediment between 100 and 150 million years old, the North Atlantic was probably about half as wide as it is today. And the South Atlantic hadn't even opened yet. It opened about 100 million years ago.

  • 12:36:24

    NNAMDIWe have -- if you go to our website you will see there the animation of the impact of the asteroid hitting the earth. That is at our website. And Doug in Bowie, Md. has a question about that. Doug, you are on the air. Go ahead, please.

  • 12:36:40

    DOUGHi, Kojo. Love your show. My main question is, if the impact 35 million years ago -- I understand the wave was big enough to cover the Appalachian Mountains -- it must have created some sort of extinction event like the Chicxulub impact, but we don't hear about it. Is there recorded in the fossil history an extinction at that time?

  • 12:37:02


  • 12:37:03

    SANFORDThat's a very good question. There were dozens of scientists studying the core from this. And some of them were actually trying to answer that question. They looked very carefully at the layers right at the time the impact occurred because there haven't really been any wide extinction events associated with 35 million years. So they were trying to look at how this impact surrounded the regional environment and perhaps the global environment. But to this date no global extinctions are associated with this impact.

  • 12:37:34

    NNAMDIThank you very much for your call, Doug. Another fascinating aspect of this discovery is what it tells us about the climate when the sea was formed. Can you talk about that and how it might relate to issues that we're concerned about today? First you Ward and then you, David.

  • 12:37:49

    SANFORDSo one of the interesting things that people are studying about during this time period, this 100 to 150 million years ago, which was the early cretaceous time period, was it was a time period when the icecaps -- for example both in Antarctica and Greenland and the Arctic weren't there. So all that water was in the oceans and sea level was higher. And also we believe the CO2 in the atmosphere was about four to five times higher than it is today.

  • 12:38:21

    SANFORDSo when we look today and think about if our climate is warming and maybe several hundred years from now these icecaps melted, what would it do to the oceans and how would it change the circulation in the oceans and what would that mean? And we can't run experiments to figure out what would happen but there's this analog in the past where those conditions existed. So people are studying the cretaceous oceans to see what circulations in the oceans might've been under those conditions.

  • 12:38:51

    NNAMDIDavid, you've described this water as an archive of past climates. What can it tell us?

  • 12:38:58

    NELMSWell, when you go out and sample these waters and they're the age of what you're talking about, you have to realize that they were recharged tens to millions of years ago. There's some things that we can use as, like, paleothermometers. And one of them is looking at the concentration of nitrogen and argon gas in the water. Once that water was recharged, that ratio is fixed and it will just stay with that parcel of water to where we actually, you know, intercept it with pumping it out a well.

  • 12:39:40

    NELMSAnd that paleothermometer really is -- that ratio of nitrogen argon, once it's fixed it's fixed at a certain temperature. So we can take the recharged temperature that we got from that ratio and compare it to the age. And basically you can just reconstruct what the temperature has been. And what we've seen in the work that we have done is our temperatures closely follow the record that they've gotten from the Greenland ice core data. And it looks like that since the last glacial maximum, there's been about a 9-degree shift in temperature.

  • 12:40:27

    NELMSBecause remember, back when we had all the glaciation there was hundreds of meters of ice to the North, up in Pennsylvania. And so the way I describe it to people, it's kind of like you open a freezer on a hot day and you get that blast of cold air. Well, that's what we had back then. And so the temperatures were much colder, by about 9 degrees Celsius, than they are today.

  • 12:40:54

    NNAMDIWe're going to take a short break. When we come back we'll continue our conversation about the sea found under the Chesapeake Bay and invite your calls at 800-433-8850. You can send email to Are you curious about how our continent and our oceans formed long ago? What do you think about the discovery of an ancient sea under the Chesapeake? 800-433-8850 or send email to You can send us a tweet @kojoshow or go to our website,, ask a question or make a comment there. I’m Kojo Nnamdi.

  • 12:43:01

    NNAMDIWelcome back to our conversation about the ancient sea found underneath the Chesapeake. We're talking with Ward Sanford. He's a hydrologist with the U.S. Geological Survey and lead scientist studying the hydrology of the Chesapeake Bay impact crater. He joins us in studio. David Nelms joins us by phone from Richmond. He is a groundwater specialist for Virginia, with the U.S. Geological Survey. We're inviting your calls at 800-433-8850, asking what you think about this discovery of an ancient sea underneath the Chesapeake.

  • 12:43:32

    NNAMDIYou know, Ward, I'd like to go back to the impact crater that trapped this ancient sea. The crater itself has a fascinating story. Where is it and how big is it?

  • 12:43:45

    SANFORDThe center of the crater, what you might call ground zero, where the impact was, was just along the coast near Cape Charles, Va. That's at the southern end of the Delmarva Peninsula, near the mouth of the Chesapeake. And the crater -- the hole it created itself was about maybe 50 to 100 kilometers across. But a lot of area around that and the coastal plains sediments were also disrupted by the crater, but that was 35 million years ago. So since that time the sediment has continued to pile up in layers on top of it. So currently it's buried.

  • 12:44:22

    NNAMDIWhat happened immediately on impact?

  • 12:44:26

    SANFORDWell, it's kind of interesting. So it sat around 100 million years ago and then suddenly there was a very bad day. And…

  • 12:44:32

    NNAMDIYeah, that was a bad day.

  • 12:44:33

    SANFORD…the asteroid came in and created a -- we can think about this from the computer simulations we've made -- it made a hole in the ground that was probably about three miles deep. And it vaporized -- all that energy from that coming in vaporized this hole, but the Earth's crust responded within minutes. It created a shock wave, tidal waves, but all that water then came surging back into this crater and brought a lot of the sediment and blocks of sediment back with it. And it filled up the crater probably in less than half an hour.

  • 12:45:07

    NNAMDIThat's what I found fascinating in looking at the animation of the impact of the asteroid hitting the Earth. You can see it at our website, It's my understanding that the impact crater is the reason the land around the Hampton Roads area is sinking.

  • 12:45:25

    SANFORDYeah, one of the things that happens when you fill this crater in quickly and you have loose sediment is that then it slowly starts compacting over time. And then as the sediment continued to deposit on top of it, it continues to compact. And it compacts more where it's thickest in the center of the crater and less in the thinner areas, where there's less sediment. And so this differential compaction can create some small faulting in the sediments. And so it's feasible that some of the subsidence of land they see down there around the Hampton Roads area is due to this compacting of sediment that's -- it's compacting very slow, but it's noticeable sometimes at the land surface.

  • 12:46:10

    NNAMDIDavid, this impact crater also affects what happens underground. And it explains a lot of things that were happening with the ground water that your team manages. Can you talk about effect of this giant crater?

  • 12:46:23

    NELMSWell, one thing, it's answered a bunch of questions that have been around since probably the turn of the century. 1900, they drilled a well at Fort Monroe, which is right down there in Hampton Roads. And they got salt water. And nobody really understood, well, why do they have salt water. In 1915 another Sanford, different from Ward -- he hadn't been -- he's not that old -- had a paper and he described what they called an inland salt water wedge in Virginia that pretty much went right up the York-James Peninsula.

  • 12:47:05

    NELMSThen in World War II there was a -- I would have to say a brilliant hydrologist, D. J. Sederstrom (sp?) , that really kind of was the forerunner of mapping. And he identified that there's something weird out here. It was the impact crater. He didn't know at the time, but he was talking about the salt water. And this wedge he described as this bifurcation of flow, or the splitting of flow in this area. He didn't really know why, but he described. And so what he was saying was, as you get fresh water in, it flushed out that old salt water. Well, in Virginia you just had this wedge that extended way further inland than most places on the East Coast.

  • 12:48:05

    NELMSOnce the impact crater was discovered, the best way to think about it, as Ward said, you've put this kind of chaotic deposit, rapidly deposited in there, well, it's low permeability, which basically means it's hard for water to move through it.

  • 12:48:23

    NNAMDIYeah, you said the crater acts like the supports on the bridge, the water goes around it.

  • 12:48:27

    NELMSIt's like fencepost. Somebody had just driven a post in here so water can't go through it so it has to go around it, which kind of explains that bifurcation. Randy McFarland, in our office, has identified areas where you actually have inversions, where you have salt water on top of fresh water. Well, that's wrong. Okay. It's not supposed to be that way. And Randy can tie it back to -- there's actually zones where water prefers to flow, so you can get that fresh water in, but since you have such a contrast in the sediments inside the crater versus those outside, it really can't get in there. So it -- what we're talking now, there's a trifurcation of flow. Okay.

  • 12:49:20

    NELMSSo it's going north and south and it's also trying to under things. So all of this has really explained a lot of stuff when it comes to flow, water quality and a lot of the geologic problems that people have been trying to answer since really the turn of the century, are starting to fall out to be due to this impact crater.

  • 12:49:50

    NNAMDIOnto the telephones again. Here is Genie, in Silver Spring, Md. Genie, you're on the air. Go ahead, please.

  • 12:49:57

    GENIEHello, there. I'd like to know if this crater was ever connected to an ocean or is always been completely separate? And if it is separate, would you ever be able to find unique fossils or anything in there?

  • 12:50:12


  • 12:50:13

    GENIELike fossils, you know, little…

  • 12:50:14

    NNAMDINo, no. I was saying Ward Sanford, not what. But…

  • 12:50:16

    GENIEOh, okay.

  • 12:50:18

    SANFORDYes. That's a good question because sometimes this is described as an underground sea and then people start thinking about Jules Verne and the "Journey to the Center of the Earth." But that's not what we're talking about. It's just water that's trapped in the sediment. And that sediment was actually along the coast, but if you think about it being along the coast during that 100 million years ago, it's that ocean water sitting there on coastline that has intruded into those sediments. So that the water in the sediments was directly connected to the ocean at that time.

  • 12:50:52

    SANFORDThere are fossils in this formation. This formation extends all the way from D.C., up Maryland, all the way southeast of the Chesapeake. And in fact they do find, for example, different dinosaur fossils throughout that formation because that was the time period that existed.

  • 12:51:09

    NNAMDIWhen you mention the size of the formation -- and thank you for your call, Genie -- you may have answered the question of Jerry, in Rockville, Md. But I will let Jerry ask the question. Jerry, you're on the air. Go ahead, please.

  • 12:51:20

    JERRYYes, thank you. I was just wondering how big is this so-called underground sea. Can you give some idea with modern comparisons? Like is it as big as the Chesapeake? Is it smaller, is it about the size of Lake Superior or whatever?

  • 12:51:48


  • 12:51:48

    SANFORDYes. That's a good question. A number of people have asked me that question after I did this and I hadn’t actually tried to measure it, but I have since then. And so if you take the area of sediment that's in the crater and the amount of thickness that this salt water exists in, and you kind of run the numbers, I came up with a number originally that was about 10 cubic kilometers. Now people don't relate to that very easily so I converted that into gallons. And that was about three trillion gallons. That sounds like a real large number, but for comparison then, the Chesapeake Bay itself is about 18 trillion gallons. So this is somewhat smaller than the Chesapeake, but still fairly substantial amount of water.

  • 12:52:31

    NNAMDIWe got an email from Majhed, who asked, "Did that impact possibly create the Chesapeake Bay itself?"

  • 12:52:39

    SANFORDSo that's another good question because perhaps very indirectly. Before we were talking about how these sediments were very loose and so they tended to compact over time. And we can actually see that in the layers of sediment that deposited above it because those sediments are thicker in the center of the crater because the crater was subsiding always in the center of the crater. So over time, when the rivers came toward the coast to flow out, they always flow out where the typography in the land surface is the lowest. Well, since the crater is always compacting, that always tends to be the area where the land is the lowest. And so it's not surprising at all now to see that the Chesapeake Bay and the ancient rivers that flowed through there were flowing in that place.

  • 12:53:22

    NELMSSo perhaps the location of the Chesapeake Bay is related to the location of the crater, although the crater itself didn't create the Bay.

  • 12:53:33

    NNAMDIDavid Nelms, we got a tweet from Eddie Water Below Water "Is there anything we can do with this discovery to assist the health of the Chesapeake Bay and its wildlife?" Do you know, David Nelms?

  • 12:53:43

    NELMSWell, most of what Ward and I have been talking about are hundreds of feet below the Bay. The one kind of implication that you can get is when you all were talking about subsidence. There is sea level rise occurring in the area, possibly due to land subsidence and other factors. And if that's happening then that can actually have implications to the ecology, historic resources, urban areas and stuff like that. So the discovery of this old water is interesting, but there's other factors that are going on that are affecting, let's say, the higher up in the system where the Chesapeake Bay actually is.

  • 12:54:43

    NNAMDIWard Sanford, this, by the way, is the second biggest impact crater discovered in the world. Where is the biggest crater formed by an asteroid?

  • 12:54:52

    SANFORDIf you look up the list now online, where the biggest craters are, I think this one ranks about tenth. And this one was actually formed about the same time as one over in Russia. And some people often think maybe it was the same asteroid that split up, but maybe not. But then as you go up in size, one of the very largest ones was in Canada, near Sudbury, where there's actually a lot of nickel mine today that's related to the original asteroid impact. I think the very largest one is in South Africa.

  • 12:55:28

    NNAMDIIt's my understanding that this was a specific project that was funded by an international consortium. So is there funding for more study and what would scientists like to research next?

  • 12:55:39

    SANFORDYeah, so this project costs well over a million dollars. And the USGS couldn't invest that money itself, but we were able to partner with the International Continental Drilling Program, who put more than half of the funds. And one of the things we did while we were drilling, we left the casing in the ground down to about 3,500 feet so that if we ever wanted to come back we wouldn't have to start again at the land surface. And so we could go back and drill even deeper if the money was available and the interest was available to do that.

  • 12:56:15

    NNAMDIYou are both part of the U.S. Geological Survey, an agency that a lot of people in Washington are not intimately familiar with. Talk a little bit about what the agency does.

  • 12:56:26

    SANFORDYes. So I mentioned a little bit at the beginning, but basically, our mission is to collect scientific data around the country, of different types, and to report that information so that we can help communities, state agencies, other federal agencies understand and better manage their finite resources, whether those be water or energy or minerals. And also help mitigate hazards, such as floods, earthquakes and volcanoes. So we cover quite a wide range of Earth science that's in the service of our citizens.

  • 12:57:09

    NNAMDIAnd David Nelms, you might want to describe for our listeners exactly what you do as a groundwater specialist for Virginia with the U.S. Geological Survey.

  • 12:57:17

    NELMSWell, we -- our main focus here, out of Richmond, is maintaining cooperative surface water and groundwater networks with the Department of Environmental Quality. We do studies with -- like Ward said -- other federal agencies, states. In this particular area we've done a lot of work with the Hampton Roads planning district and the DEQ here in Virginia. Our main thing is really monitoring the resource and then we do the interpretive studies to get an idea of what's going on in particular areas.

  • 12:58:00

    NNAMDIDavid Nelms, a groundwater specialist for Virginia, with the U.S. Geological Survey. David, thank you for joining us.

  • 12:58:06

    NELMSThank you, Kojo.

  • 12:58:07

    NNAMDIWard Sanford is a hydrologist with the U.S. Geological Survey. He's the lead scientist studying the hydrology of the Chesapeake Bay impact crater. Ward, thank you for joining us.

  • 12:58:15

    SANFORDThank you, Kojo.

  • 12:58:16

    NNAMDIAnd thank you all for listening. I'm Kojo Nnamdi.

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