Well, this is one of the nicest
ways I've spent a Tuesday morning in a while — just sitting in
the woods looking at rocks. Hey there! So, this is a new kind of video for
me. I am super excited about it. I even broke out the fancy bow shirt. And I think you're
going to learn a lot, and I hope you enjoy it. So kick back, relax, and let's jump in. Hey there! Right now, I'm in Houghton, Michigan —
specifically, I'm on the campus of Michigan Tech University, and I am here to see a boulder
that is kind of dramatically out of place. I first saw this thing when I was here back in
May. And while it totally piqued my curiosity, I had no idea what kind of
adventure I was about to go on. Hello, old friend. So, this boulder doesn't look like much, but
what caught my attention the first time I saw it wasn't the rock itself, but the sign next to it.
According to the sign, this boulder was collected from near Marquette, which is a city about 70
miles from here as the crow flies. But that's not where this thing started. In reality, the
material that makes up a lot of this boulder was blasted over to Marquette at supersonic
speeds from Sudbury, Ontario, some 300 miles away. Turns out, about 1.8 billion years ago,
there was an enormous meteorite impact near Sudbury — one so large, it blasted
debris as far as modern day Minnesota. And also, it might have changed the
composition of the nearby oceans. I had never heard of this thing, so I immediately
got online and started researching — except, in trying to read up on this topic, I quickly
realized that I was getting out of my depth. There was enough context and back
story that I risked getting the facts seriously wrong if I tried to dive in on my own. So I got some help. Meet Dr. Bill Cannon. He's a Scientist
Emeritus with the U.S. Geological Survey and might be one of the coolest people I've ever met. Back in May, I kept seeing his name pop up in
papers about the Sudbury Impact, so I reached out and asked if he'd maybe be willing to do
a video call to answer a few of my questions. Turns out, he was going to be in Marquette in
September. So a few months after that initial email, we met up at this little, unassuming
roadside park, about 15 minutes outside the city. And I learned so much. Like, here's
something you need to know about Dr. Cannon. When I say he's an expert in Marquette geology,
that's almost an understatement. Check it out. [Alexis] Bill, how are you?
How are you doing this morning? [Bil] I'm fine. It's a
cool, somewhat damp morning. But we're used to that kind
of thing around here, so... [A] I feel like, in the very short
amount of time, I've talked to you, I just get the impression that, like... Do
you know more about geology in Marquette than anyone or am I just hyping you up too much? [B] I'm probably well up the list... because
I actually started working here 54 years ago. [A] Yeah! [B] And I've done many other things; I don't
want to apply I've been here for 54 years. But Marquette and the Lake Superior area in
general have been one of the focuses on my career. So, I've... yeah. I know... How
would I say it? Quite a lot. More than most people about
the geology here, so... So, Bill knows his stuff. And among other
things, I got to chat with him about how our understanding of the Sudbury Impact
has changed in the 54 years he's been studying this area. But first, here's some
of the backstory he helped me understand. So, about 1.8 billion years ago, there wasn't
any big life on Earth. Most things were tiny, like phytoplankton. These organisms were
hanging out in seas around the planet, and some of them were producing
oxygen through photosynthesis. Overall, it was just a cool time in Earth history, and the planet was getting closer and closer
to the place we recognize today. But then, one day, a rock came screaming in from
space. And it wasn't just any rock. This one was the size of a small city. [B] A good, good, reasonable assumption
is that the impacting body was between 10 and 15 kilometers in diameter.
[A] Wow. [B] Which is a big, big hunk of rock. [A] Yeah. [B] And
of course, again, another important factor in the amount of energy transmitted
into the Earth is how fast it was moving. Because the amount of energy in an
object is proportional to its mass times, its velocity squared. And the
velocity is the thing we know the least about. So you can understand that
there's a big, big range of estimates. The crater itself has been estimated on the
small side to be 150 kilometers diameter. And on the large side, 250. So, it's reasonable to
think about it as something like a 200 kilometer diameter hole blasted in the ground, and they
excavated down to perhaps 30 or 35 kilometers. [A] Wow. Now, today, you won't see, like, a
giant pit at Sudbury. There's been a lot of erosion and other activity over
the last 1.8 billion years. But regardless, that former crater isn't the only
thing this impact left behind. It also flooded the surrounding area with debris, so much so that it formed a new rock layer more
than 130 feet thick, nearly 300 miles away. But before we get into that, what really
struck me about this story was the fact that for a long time, geologists didn't
think there was an impact here. Subarea is a major nickel mining district.
So by the 1960s, people had been doing geological work there for a century. But
even then, they just thought there was some weird volcanic rock there. That is until
a scientist named Bob Dietz came along. Today, Dietz is more well-known for his
work in oceanography and plate tectonics. But in the early 1960s, he published
a paper with this wild idea that those rocks at Sudbury were thanks to an impact.
He based his hypothesis on the existence of shatter cones in some of the rocks, which he
interpreted as evidence for a meteorite impact. And well, let's just say that
idea was not received super well. When you first started in this area.
What was the state of knowledge like? [B] Well, that was... I started here in
1967. This is almost my 54th anniversary, just a few days ago. [A] All right. [B]
And in terms of the Sudbury Impact, it was a very new, very controversial idea at
that time. Hardly anybody believed it. People have been studying the geology of Sudbury for literally a century because it's a
major mining district. And an American oceanographer named Bob Dietz, after
spending a few days at Sudbury, suggested that this was probably a meteor impact
based on some unique features that he saw there. And he was viewed as a heretic — just absolutely
out of, out of his mind. But pretty quickly, some other people began to find other evidence
that, yeah, maybe this was an impact. And over all that time, you know, 50 years or more, it's
become almost universally accepted that much of the geology at Sudbury, including the major nickel
deposits were created by this giant impact event In fact, it's interesting that that the city of
Sudbury there, because of the nickel deposits, and the nickel deposits are there because of
the Sudbury impact. Kind of an interesting illustration of how events in
the way back geologic past, can still have an effect on what's going on today. Now, I mentioned that Bill and I met up at this
little roadside park outside of Marquette, and that wasn't just for kicks. This roadside
park is also home to the McLure site, which is the best place in Michigan to see
the wreckage the Southbury impact left behind. And what I was curious about was
how geologists knew what they were looking at here in the first place.
But, of course, Bill had me covered. [B] This was one of the latter ones that we
had recognized, although it was mapped in the early '60s. In fact, I first saw the site with a
colleague in 1967. [A] All right. [B] And he had mapped it, and he showed me this funny breccia
and we agreed: That's a funny breccia, alright. Actually, some colleagues in Canada had
recognized the layer up there near Thunder Bay, and they showed us what it
looked like. And we immediately thought, "Oh, yeah, we know
where it is in Michigan." When we first looked at it, we were not very
certain that it really was ejecta. [A] Sure. [B] But the sort of the smoking gun of identifying,
proving something as a meteor ejecta something called shocked quartz. And this is a sort
of sand grains of quartz, a common mineral, that has been... received, such a strong
shockwave that it's made changes in the crystallographic structure that is
quite easily to see under a microscope. If you don't find that, the skeptics
will never believe that you have a meteor impact. But that's critical to find.
And we, we did eventually find it here. And then it was it was a slam dunk that this was
really part of the ejecta material from Sudbury. And then, of course, came my
favorite part of the morning. [A] Well, on that note,
wanna go look at some rocks? [B] Let's look at rock. [A] All right. [B] It's
what I do. [A] All right, into the woods we go. [B] That's probably the... the best piece to see features in. You wanna
scramble over there, and...? [A] Yeah. I feel... part of me, I'm just like, "It's a rock, I can sit on it," but there's a part of me
that's like, "But it's a significant rock!" [B, laughing] That's all right. [A] Well, this is one of the nicest
ways I've spent a Tuesday morning in a while — just sitting in the woods
looking at rocks. What are we looking at? [B] Okay, well, we'll take a closer look at
some of the material that makes up this layer of impact-related rocks. And there's a general term
called ejecta for these kind of rocks. It simply means material that's been ejected forcefully
out of the crater by the, by the impact blast. So in here, we can see... we've heard of this and also a general term is breccia. We can see these
large angular fragments of lighter-colored rock. And these are most likely derived from the rock
layer immediately beneath this ejecta material. This material came over it ripped up some
of that material and incorporated into into this. [A] Wow. [B] Hard to see on this,
but you can see some little indentations, pits all over this. And they are little
fragments of what was glassy material. And this was material that was not just physically
broken, expelled from the crater, but was heated so much by the impact energy that it melted
and it came out of as little particles of basically lava. And they have,
again, blown 500 kilometers to here. And they'll make up a good deal of the finer
grade material on here. So this is quite typical of what the rock here at McClure looks like. There are many different ways in which you can form an ejecta layer. And this is one that we
interpret to be what we call a ground surge. That means that the solid rocks that are blown from the crater come on ballistic
arcs at supersonic velocities. And when they hit the Earth — if you throw
a rock today, it doesn't hit and stop. It hits and skips and moves on by its own
momentum. And that's what our interpretation is of this. This was a great mass of
rock coming on ballistic arcs, hitting the Earth at supersonic velocities, and then
kind of screaming across the Earth's surface and tearing up everything that it came in
contact with until it finally slowed down and settled out in a layer that
here is about 40 meters thick. So it's a very thick layer.
And it seems to be all just one event that's just... Right now,
you had 40 meters of new rock here. [A] Yeah, and that would have been a fast
process, right? Like a Wednesday... you've got what was it, banded iron
formation was the rock layer here? [B] Right. [A] Yeah, Wednesday. You've got banded iron
formation. And then what, Thursday? Friday...? [B] The first probably takes... this would
have arrived only minutes after the impact. [A] Oh, well, then, okay! [B] You know, it's coming out at some kilometers
per second, so there's not that many kilometers between here and Sudbury.
So it gets here in a hurry, and settles out in a hurry.
So it's perhaps only minutes. This kind of blew my mind,
just thinking about how fast this region of the Earth changed. Like
the day before the impact, the sediments that were being laid down here created a
rock layer called banded iron formation. It's kind of stripey, and it formed in the seas
or oceans. Bill shows me some in the next clip. But then, this impact comes
along and suddenly — no more banded iron formation. This rock
never forms in this region again. So what happened? It seems like something
about the composition of the ocean drastically changed — definitely in this
region, and possibly on a global scale. Maybe it was some kind of extinction event
where a bunch of phytoplankton disappeared, or maybe it was something else
— we just don't know yet. Oh, and also we haven't even
talked about the earthquake. [B] So as we look at a rock face like this, we're
seeing the oldest rocks here getting younger, younger, younger as we go up. These rocks here,
that you can sort of see a layer structure in, is the top of a band of iron formation. Bit of a close up, not real clear. But you can see
this lighter greenish layer is a chert layer. And then these other units are more iron rich units.
[A] Oh, okay, yeah. [B] So these are called banded iron formations because there are bands of
cherty rock, iron rock, cherty rock, iron rock. These were the last layers of iron
formation that were being deposited before the impact event. As we look at this
material here, we can see that there are... pieces of chert, these lighter bands... but they're
not continuous layers and they're not in place. They've been broken apart and jumbled around a
bit. And our interpretation of this is that this breaking apart was created first by the enormous
earthquake that was set off by the severe impact. By some estimates, it could have
been a magnitude 11 earthquake, which is greater than any
earthquake you can create on Earth. So when the earthquake arrived here, it
actually broke apart some of this iron formation into small fragments and kind of jostled
them around. They are stacked up with open spaces. And then when the ejecta arrived, it actually sort
of filtered down in and filled in these spaces. And then as we go this way, it's successively
younger. We get less chert, although there's still quite a bit. Up here, for instance, we
can again see these angular fragments, which are pretty clearly derived from this material
here, but they're a little more transported. They are now floating in this
matrix of glassy ejecta material. So you've got this story where a
rock comes screaming in from space, hits what's now Ontario, and creates a
whole new rock layer in Marquette, Michigan and beyond. And along the way, it might have also,
you know, changed the composition of the oceans. One question I had for Bill is what geologists
are still trying to learn from this site. And partly, he mentioned that they're
now trying to use this Sunbury layer to better understand the iron deposits
around Michigan's Upper Peninsula. But also, there's this. [B] And I think a bigger question, and I'm a
little disappointed that nobody has followed up on this... Is there really a mass extinction that
has changed...? Or what happened that changed the way the sediment in the ocean was depositing
the day before and the day after the impact? That's a really big change in what the ocean was
doing, and we don't have a very good explanation for that yet. [A] Sure. [B] I think there's a very fruitful area for research on that.
Cool. Open for anybody that wants to do that. [A] Open for anybody who
wants to do that, he says. So if you're looking for a
thesis idea, there you go. Now, I learned so much from Bill, but one last
question I love to ask people as we're wrapping up is that, if somebody takes away one thing from
this conversation, what should that thing be? So, as we wind down the
story of the Sudbury impact, I'll leave you with one more clip —
one that's not just about the rocks, but it's also about the ordinary incredible
people who've helped us understand them. [B] Oh, I think... you have to be open to a
totally new idea. You know, people thought they understood this for a long time and they
were, you know, it was totally, totally wrong. So, be open to that, and don't get too
focused in on traditional interpretations. If you didn't have a bit of an open mind, you
know, we would have just gone past this. And the... Actually, the people that discover this,
that's a little interesting side story, in Thunder Bay. They were two retired high school teachers,
who had no geologic experience whatsoever. Greg Brumpton and Bill Addison were their names.
But they had a lot of curiosity, and they had read about the Chicxulub impact. And they realized that
in Thunder Bay, there's a situation where there's a rock unit that is full of algal stromatolites,
and it's got a black slate right above it. So they theorized, maybe this was related to the
Sudbury Impact. And they spent about ten years of their own time trying to find this,
learning more about geology, and finally found it and proved that it was [from] the impact. So that was really the first discovery. And
that's what led to, you know, ourselves and other people being able to find this around
the Lake Superior region. And that's a pretty remarkable story of those two individuals
that stuck with us for ten years. [A] Cool! That's great. Well, Bill, thank you again so much. I feel
like I have learned so much. I hope people learn cool things from watching this.
I'm just really grateful for your time. [A] Well, it was a pleasure doing
it. It's always nice to pass on some of our information in a way that is not
just in highly technical papers that most people aren't going to see. And will learn what's
here and the have some appreciation for it. [A] Yeah! Sory of my life. Thanks for joining me for this adventure.
If you liked this video. I'd be honored if you were willing to share it with a friend or
on social media. This was a big thing for me, and I would love for more people
to get to learn from Dr. Cannon. In the meantime, thanks again
for being here and also a huge special thanks to the folks who support my
work on Patreon, on who genuinely made this whole new kind of video possible. One
way or another, I'll see you next time.
