[APPLAUSE]
FRANCIS A MACDONALD: All right.
Trudging up here
in my snow boots,
I'm really excited to
introduce Mark Richards, who
is the Professor of Earth
and Planetary Sciences
at University of
California Berkeley.
Professor Richards's research is
focused on understanding really
large-scale dynamic processes
of the interior of the Earth
and other planets and how
those processes really
affect geological phenomena that
are observable at the Earth's
surface, so that is he
combines physical theory
with geological observations
to test hypotheses
about the nature of the Earth
and how the Earth works.
And Mark-- he's best known
for his work on how thermal
anomalies deep in the
interior of the Earth,
that they result in mantle
plumes, which come up
to the surface and create
these large igneous
provinces and hot spots.
You can think about Hawaii,
or the Galapagos, or the topic
of today's lecture, which
is a Paleo example, which
are the Deccan Traps, a large
igneous province in India.
Professor Richards, he earned
his BS in engineering science
from University of Texas in
1977 and his PhD in geophysics
from Caltech in
1986-- my alma mater.
He joined the University
of Oregon faculty in 1987.
And 1989, moved to UC
Berkeley where he's held
many, many leadership roles.
And I'll bring out
a couple of these
because these are impressive
considering the science
that he's currently doing.
From '97 to '99 he
served as the Chair
of their Earth and Planetary
Science Department.
And then from 2002
to 2014, he was
the Dean of the Mathematical
and Physical Sciences.
And from 2006 to 2014,
he was the Executive Dean
for the College of
Letters and Sciences.
Now during that time,
he tripled the amount
of fundraising for
the colleges, and he
spearheaded integration
of different disciplines
to create an innovative,
"big ideas" courses
for undergraduates and made
significant contributions
to the increase in minority
representation in STEM fields.
Now keep this "big
ideas" concept in mind.
Despite all these duties that
he was doing at UC Berkeley,
Mark has managed to
continue his research
and come up with
his own big idea.
And particularly, his
big idea that he's
going to talk about
today is a new idea
on how and why the
dinosaurs went extinct
65 million years ago.
And this is such a big
idea, that The New York
Times decided to cover
it in Sunday's Opinion.
So instead of me
going into it, I'm
going to let Mark go into it.
And I'm happy to introduce Mark.
Let's welcome him.
[APPLAUSE]
MARK RICHARDS: OK.
So we start here.
The subject of the
Cretaceous-Tertiary mass
extinction is the subject of an
infinite debate and interest.
And now this is not
working, so I'll use this.
There we go.
And this is-- of
course, we lost T. rex.
This is one of the
largest mass extinction
events of the Phanerozoic era,
the last 600 million years
or so.
Wiped out about 70% of species--
marine and terrestrial--
and killed the
non-avian dinosaurs.
Of course, the
birds are dinosaurs,
and they managed to fly
through this unscathed.
And most interestingly
and probably the reason
for fascination, is
that it led to this.
This is a diagram.
I'm not a paleontologist,
so disclaimer here.
But this is a diagram of
the explosion indicating
the explosion of
mammalian species
at the Cretaceous-Paleogene
boundary.
The formal boundary is known
as Cretaceous-Paleogene, not
actually Cretaceous-Tertiary.
So here's the impact.
Here is the boundary.
And these little
critters, furry things
called mammals that
were crawling around
under rocks and stones,
suddenly blossomed when
you got rid of the dinosaurs.
And that's why we're here.
And so the ecological
niches were opened up,
and intelligent life evolved.
And if not for whatever
happened 66 million years ago,
intelligent life
probably would still
be waiting to bloom
on this planet.
So it's an interesting event.
And 66 million years
is the wink of an eye
in the 4.5-billion-year
geological history
of the planet, so it was
actually quite recent.
I mean, these
critters that died off
had arms, and legs, and brains,
and eyes, and stuff like that.
They weren't all that
genetically different from us.
In 1977, Walter Alvarez, a
young geologist at Berkeley,
brought this rock--
literally this rock--
to his father, the famous
Nobel Laureate Luis Alvarez,
at Berkeley.
And he had a question.
This is in a hand sample that's
much smaller than this picture,
of course, the
Cretaceous-Tertiary boundary.
These are the Cretaceous
limestones here
from Gubbio, Italy.
These are Cretaceous
limestones that are pink.
And if you look closely at this,
you can see these little dots.
These are foraminifera, little
critters that live in the sea.
And these are large enough
to be seen by the naked eye.
Whereas, the foraminifera
that survived
the Cretaceous-Tertiary
boundary are
too small to be seen because
the big ones all died off.
In fact, most of them died off
and replaced by other species.
This is a very abrupt
boundary, seemingly so,
in the paleontological record.
What Walter wanted to know--
there's this boundary.
It was called the boundary clay.
That's a few centimeters
thick at this location.
How much time was represented
by this boundary clay?
Now this turns out to be a
profound question geologically
speaking.
And especially 37 years ago,
when plate tectonics was
relatively young and what
are called the uniformitarian
ideas of Charles Lyell's
great treatise in geology
from the 19th century
were holding great sway.
And the idea of catastrophes
in the geological record
were very taboo.
And it's very
interesting to be saying
this in the land
the Stephen Gould,
of course, who modified that
view considerably as well.
But there was, needless to
say, the idea to be tested
was how much time elapsed here.
Was this a day?
Thousands of years?
Or even millions of years?
And Walter thought
that his father Luis
might have some whiz bang
physical method for figuring
out how much time there was.
And he did.
He decided to look at the
platinum group elements
because they come
in with cosmic dust
at a relatively regular rate
and thought that if they could
figure out how much the
abundances the platinum group
elements were, then they
might be able to figure out
how much time had elapsed here.
Now you all know that-- most
of you know the punchline.
What was discovered was that one
of those elements they examined
by neutron activation
analysis turned out
to be an enormous
spike of iridium that
could not be accounted for
by any terrestrial cause.
And so they invoked the
famous Alvarez hypothesis
of 1980, which is probably
the most cited paper
in the entire
geological literature.
And of course, if you
ask any of your children
what killed the
dinosaurs, they will
say a big rock fell
from the sky, a meteor,
and killed the dinosaurs
because meteorites
bring iridium and
other rare elements
that we don't normally find.
The fly in this ointment is
that at about the same time,
66 million years ago, the
Earth was experiencing
one of the largest sequences
of volcanic eruptions
in the Phanerozoic era,
the last 600 million years.
And that's called the
Deccan Traps in western
and northwestern India.
Now when I say large,
let me be specific.
The amount of lava
that was erupted
over a period of
approximately a million years
was enough to cover the state of
California two kilometers deep
or the lower 48 states
of the United States
about 200 meters deep.
And you can imagine that along
with that lava, as illustrated
by these photos from this
unpronounceable volcano
in Iceland recently, comes a
lot of effusion of noxious gases
into the atmosphere,
particularly carbon
dioxide and sulfur, which
gets aerosolized into sulfates
in the atmosphere and does
all sorts of nasty things
to the environment.
So the problem that has
been with us for so long
is what, of course, really
killed the dinosaurs.
Now the most accepted
theory is the impact theory.
There are a lot of reasons for
that, which I will not go into.
But there has been a contingent,
a very vocal contingent,
contending that volcanism
is the primary culprit.
Now I want to put a
disclaimer out right now
for this full-packed audience.
And you can all go home
if you're disappointed.
I don't know what really
killed the dinosaurs.
And the fact that I can say
that and be very best friends
with Walter Alvarez at
Berkeley should tell you
something, which is this is
a very, very rich story that
has a long way to go.
And it's moving very,
very fast right now.
And what you're going to
see is a work in progress
that we are very excited about.
In fact, I'm going to tell
you up front that there
are a couple of-- especially
one extremely technical slide
that I'm going to
put in front of you.
And the reason for that is that
it's just now being published,
and there has been no time
to develop the Reader's
Digest condensed artist's
conception version of some
of these materials.
And I'll do my best to explain
them you in a fashion that
doesn't put you to sleep.
All of these co-authors,
including Walter Alvarez,
are very distinguished
scientists in their own realm--
Steve Self being perhaps most
distinguished volcanologists
I know, Paul Renne, perhaps
the best geochronologist
on the planet, and Jan
Smit, who is really
the co-discoverer of the
Cretaceous-Tertiary Impact
published in the same year.
It should really be known as
the Alvarez-Smit hypothesis
properly.
And Sally Gibson, who
is a distinguished
geochemist at Cambridge.
Every one of these
co-authors are
people who have tried to
prove the outrageous idea I'm
going to tell you about wrong.
And in every case, the evidence
that they brought to bear,
which was considerable, ended
up either being consistent with
or supporting the
hypothesis that I'm
going to suggest to you.
So when you're a scientist,
the more outrageous your idea
and the more outrageous
your hypothesis,
the harder you are obligated
to try to show that it's wrong.
This is something that separates
science, perhaps, from religion
that people don't
understand so well
some time is that in science,
when we have an idea,
or a doctrine, or a
theory, or something
that becomes accepted,
the best thing
you can do in science,
often, is show
that the other fellow is wrong.
And the best thing
you can do when
you have a new idea is
to-- that you should do--
is try to find everything
that's wrong with it.
We are trained skeptics.
That doesn't mean we don't have
some optimism in our bones.
But this is really a
story, in many ways--
although I'm going to flash
through an enormous amount
of territory technically
without explaining in detail.
An awful lot of
this story is trying
to find evidence that either
supports or, better yet,
refutes an outrageous idea.
So then, I'm going
to show you the two
slides of this entire
presentation where I'm actually
an expert on the subject.
And this is the first one.
In 1989, the year
I came to Berkeley
and met Walter Alvarez,
I published this paper,
which is my most cited
paper, as a theory
for how, as Frances
mentioned, large igneous
provinces in hotspot tracks.
So like Deccan Traps is
a large igneous province.
Hawaiian-Emperor chain
is a hotspot track.
I published a theory
about how that works.
And these are the
older observations,
but this is from
the original paper.
And germane to this
study is that here we
have the Kerguelen hotspot,
which is currently active.
And there's a track
going back in time
along this trail of
volcanoes that get
older and older-- excuse
me, I'm on the wrong track.
There's the Reunion
hotspot track.
If we go back along this
trail, along this trail,
back to 66 million years ago,
when the Indian subcontinent
was actually sitting
above this hotspot,
and you had this
enormous outburst of lava
called the Deccan Traps
that covers this area.
There are many other
such pairs, the Galapagos
with the Caribbean Plateau,
the Yellowstone hotspot
and the Columbia River Basalts
of the northwestern United
States, et cetera.
And the explanation for that
that is still widely accepted
but might still be
wrong is that these
result from hot thermal
plumes in the mantle
in this following fashion.
This is literally a shadowgraph
shining a projector light
through the side of
a vat of corn syrup
that's being heated from below.
And corn syrup has a
strongly temperatured event
at viscosity.
It gets more runny
when you heat it up.
And the form of upwellings,
plumes, like in a bowl of soup,
you get from that are these
large, bulbous heads that
are followed by these
conduits that feed them
from this hot boundary layer
down here where you're heating.
And so the theory
is that the heads
form these big splotches
of large igneous provinces
that come out very fast.
And the tails form
these nice hotspot
tracks like here and along
the Kerguelen Ninetyeast
Ridge and the Tristan
de Cunha hotspot
track in Hawaii, which
isn't on here for reasons
I won't go into.
Now here's where it
gets really thick.
Get ready to suspend disbelief.
This is a stock
diagram showing what
are called the big five mass
extinctions of the Phanerozoic,
not including the one
that we're inducing
right now, in the Holocene.
These are, for example, here,
at the Cretaceous-Tertiary
boundary, about 50% of
the [INAUDIBLE] families
disappeared as indicated by
this little thing diminishing.
There is an extension at the
Triassic-Jurassic boundary
about 200 million years ago.
The largest extinction of all is
the Permian-Triassic extinction
at 250.
And then the end Ordovician
and the Devonian,
which I won't talk about today.
Here's the problem.
Of the three mass
extinctions that
have occurred since
250 million years ago,
they are all very
precisely associated
with large flood basalt
volcanism, large igneous
provinces, like the Deccan
Traps for K-T boundary,
the Central Atlantic
magmatic province
at the Triassic-Jurassic
boundary,
and the Siberian Traps at
the Permo-Triasic boundary.
So they outlier is
the Chicxulub Crater
or the K-T impact at K-T time.
There is no evidence
that is widely
subscribed to for impact at
any of these other boundaries.
It gets worse.
The Permian-Triassic
boundary was recently shown,
understood to be double
boundary with a peak
here at the end of the Middle
Permian or Guadalupian period,
and then the bigger peak
at the end of the Permian.
And the Emeishan Traps
eruptions in China
were 260 million years
ago at this little peak.
And then the Siberian
Traps are here.
So actually, the last four
mass extinction events
for which we have
the best record
are all associated with massive
volcanism on the planet.
And only this guy, the
Cretaceous-Tertiary boundary,
is associated with
mass extinction.
You can kind of see Charles
Lyell rolling in his grave
here because this is
really confounding.
How could this possibly happen?
You could not make up a greater
geological quandary than this.
And it's basically been with
us for 3 and 1/2 decades.
And a lot of people had
just plain given up.
Well, we didn't give up.
I've had lunch almost
weekly with Walter Alvarez
for 25 years.
And whatever else
we're discussing,
it always comes
back around to this.
God dammit, we're going
to have to figure out
what happened sometime before
we retire because it's just too
good a problem to let go.
Well, let's see.
This isn't advance.
OK.
In 1991, Alan Hildebrand
was doing his PhD thesis
and rediscovered what
Panex geologists in Mexico
had known about
since the '50s, which
is there is a large impact
structure here spanning
the north coast of Yucatan,
which has subsequently become
known as the Chicxulub Crater.
It's about 200
kilometers in diameter.
And it was known to be at
about Cretaceous-Tertiary time,
about 65 million years
ago, but not exactly.
And there are all sorts
of tsunami deposits
around the Gulf of
Mexico that actually
led Alan Hildebrand to start
looking for this to begin with.
In 1991, Walter
Alvarez, here, who
had since become good
friends with Jan Smit,
the co-discoverer of the
evidence for the impact,
visited a locality
near Mimbral, Mexico
and found an enormous
tsunami deposit
that was right at the
Cretaceous-Tertiary boundary
in this exposed section.
And that really was
convincing evidence
enough for many people,
and subsequently,
very high precision
radiometric dating
using the argon-argon
method has actually
shown that the
ejecta blanket around
the globe from the
Cretaceous-Tertiary impact,
from the Chicxulub impact,
matches within 30,000 years
precision the actual
biostratagraphically defined
extension boundary,
which is really
an astonishing accomplishment.
And so Walter
published this book
which if you haven't
read it, you should.
Because it's one of the finest
pieces of science writing
you will ever find-- T.
Rex and the Crater of Doom.
And one might have
thought that this would be
the end of the story in 1991.
But for the reasons I've
just shown you, obviously,
it's really not.
And unlike things such as the
question of global warming,
this really constitutes a
genuine scientific controversy
even today.
This is a quote from
paper published in 2010
by Schulte and 39 co-authors.
The end of this says,
"lead us to conclude
that the Chicxulub impact
triggered the mass extinction."
And this is a quote
from Keller et al.
in the same issue of Science
with five co-authors saying,
"Deccan database indicates
a long-term, multi-causal
scenario and is inconsistent
with the model proposed
by Schulte et al."
Now in science, we don't
count bodies or witnesses
because we don't vote on
whether things are right or not.
We go out and try to figure
out what actually happens.
And in this case, in what
I'm going to offer you today
is a possible reconciliation
of these views
that two years ago I would
have laughed at if somebody
had suggested it to me.
So flash forward into how I
got back into this business.
How I got back into
this business was
I took my family on a diving
excursion to Cozumel, Mexico.
And in that process-- this is
my son here having a good time.
I'm sure he would
be really unhappy
if knew I was showing
you this slide,
but I'm 3,000 miles away.
I can get away with that.
We took a bus excursion
to Chichen Itza,
the great Mayan civilization,
great city in Yucatan.
And they built these
magnificent pyramids.
This is actually one
of the smaller ones.
This is one of the bigger ones.
And the reason they were able
to construct this civilization
where there is marvelous
limestone sinkholes--
the impact, by the way,
hit limestone, which
is another part of this story.
But these limestones sinkholes--
these are steps here.
So you get an idea of the scale.
These gorgeous,
freshwater sources
allowed people to establish
civilization in this area.
Now here's an interesting map.
It's a little blurry here,
but the white dots-- this
is Chichen Itza here.
This is the north
coast of Yucatan.
And the white dots
here are the locations
of these cenotes These
sinkholes are called cenotes.
And Walter had showed
me this diagram just
before I left on vacation
because, you know,
I was going to Yucatan.
I had to go talk to
Walter about Yucatan.
And he pointed out
that these cenotes
are excluded by this
ring here, which
is the edge of the gravitational
anomaly of the Chicxulub
impact in Yucatan.
So I was impressed with the
fact that the shattered rock
in here, for the most part,
can't support these sinkholes.
And I came back
to my hotel room.
And I had about as close to
what you would call an epiphany
as you get in this business.
And so I want to
tell you I literally
sat up bolt straight in my
bed at 3:00 in the morning,
got out my computer while
my family was asleep,
and started searching the
literature for something that I
will show you in a minute.
So the previous
summer before, I had
gone on a rafting trip
with Leif Karlstrom, who
was a graduate student of
mine and Michael Manga's
at UC Berkeley.
Leif happens to be one of
the finest bluegrass fiddle
players on the West Coast and
a brilliant graduate student.
And he'd be telling
me about something
like that he and
Michael Manga and others
have been doing a lot
of work on the observed
triggering of volcanoes
by earthquakes,
which is a widespread phenomenon
and very well documented.
And here's the diagram.
Here's the first of one
those technical diagrams,
which I will try to take the
time to explain to you here.
This is a result of that work.
On the bottom axis here,
is earthquake magnitude,
so this is a modest sized
earthquake, a 5 or a 6.
These are very large
earthquakes, magnitude 8 and 9.
And on this diagram
is a log plot,
so we have 10 kilometers, 100
kilometers, 1,000 kilometers,
10,000 kilometers distance
away from earthquakes.
And these blue and
red dots represent
triggered eruptions, volcanic
eruptions, by earthquakes.
So the very largest earthquakes,
for example, magnitude 9
earthquakes like the
one in Tohoku, Japan,
are known to trigger
volcanoes for distances
up to a number of
100 of kilometers,
700 or 800 kilometers possibly.
But actually, the distance is a
little bit smaller for reasons
I won't go into.
But there's an energy threshold.
And these contours
gives an energy
threshold for the
triggering of volcanoes
by earthquakes as a function
of magnitude and epicentral
distance.
And these contours-- this
is 0.1 joules-- that's
a measure of energy--
per cubic meter.
So this is an energy
density of 0.112 and 100.
And the basic threshold is
something like 0.1 to 1 joules
per cubic meter required
for earthquakes to cause
incipient volcanoes, that is
volcanoes that might be sitting
around gaining enough umph
to erupt to actually go off.
And this is now a
well-documented phenomenon.
Chicxulub, the Chicxulub
impact was approximately
a magnitude 11
earthquake, which is
kind of like having a magnitude
9 earthquake everywhere
on the planet, if you
can get the idea, which
is an event unprecedented,
of course, in human history
and may be unprecedented
other than this
for the entire Phanerozoic era.
Because this is the largest--
the Chicxulub impact
is the largest impact we
have in the last billion
years of Earth's history
that we know about.
If you scale this
plot-- and I admit
that that is a stretch because
the physics here is unknown.
If you scale the Chicxulub
impact at magnitude 11,
you find that the
energy densities
are sufficient to
trigger volcanoes out
to 10,000 kilometers, which
means effectively globally,
that the entire volcanic
system, including
the mid-ocean ridges, arc
volcanoes, and the Deccan Traps
were susceptible to being
thrown into an unusual phase
of eruption by the
Chicxulub impact.
Now I told you something
that maybe you've forgotten.
But the Deccan Traps
volcanism was already
underway for at
least a million years
before the impact occurred.
We know that very well
from the geochronology.
So the impact could not
have caused the volcanism
as a fundamental cause, but I'm
going to get to it in a minute
a model for how this might have
happened for a volcanic system
that was already under way.
Here's another key
piece of information
that imminent
volcanologist Stephen
Self brought to my attention
a little over a year ago.
And he pointed out that
there's the Deccan Traps
and there's the Deccan Traps.
This is a map of the
Deccan Traps volcanic area
and in northwestern India.
This is the city of Mumbai here.
For most of the history
of the Deccan Traps,
the lava flows were restricted
to an area about this size.
This is one of the lava
flow formations called
the Thakurvadi, which actually
didn't constitute a major flood
basalt event at all.
And then within this sequence
of eruptions and, it turns out,
probably very suddenly, there
were these enormous eruptions
that I will refer to as the
Ambenali and Mahabaleshwar
flows, or alternatively
as the Wai subgroup flows,
that covered an area about
the size of France or Texas
in probably only 100
or 200,000 years.
Some of those
flows were so large
that they went down the
Krishna paleovalley,
and flowed into the Bay of
Bengal on the east of India,
flowing at least 1,000
kilometers and maybe 1,500
kilometers from their source.
If you can imagine single lava
flows 10,000 cubic kilometers
in volume and flowing
from here to wherever
1,000 kilometers from
here-- I don't know,
Chicago or whatever.
That's an impressive current.
Now I'm going to show you
another technical slide,
but this one is comprehensible,
so stay with me.
This is called a
stratigraphic section
in geology, where we
put time on the bottom.
Time goes from bottom to top.
This is old down here
and young up here.
And the Deccan basalt
group of formations,
which is about 3 and 1/2
kilometers thick in aggregate
of lava flows, is divided up
into the Kalsubai, Lonavala,
and the Wai subgroups,
which are subdivided
into these formations, which
I will not pronounce to you
or it would take most of
the rest of my lecture.
Now these lava flows are
indicated by their thickness
in situ, where they're
mapped stratigraphically.
So this amount of
time here represents
approximately a million years.
But it turns out that
those immense lava
flows that I was talking
about, these huge flows,
were restricted to just
mainly these two formations
and a little bit of this, so
really, Poladpur, Ambenali,
and Mahabaleshwar with the
big act being Ambenali.
And these are called
the Wai subgroup flows.
And the volumes-- the
shading is a little faded
by the lighting here-- but if
you scale the volume of flows
by the area times the
thickness of the formations,
everything that happened up
through the Bushe Formation
in the Lonavala subgroup was
relatively small in volume.
And the total
volume here is only
a couple hundred thousand
cubic kilometers,
which is small compared to
large flood basalt events.
70% of the volume
of these eruptions
occurred within approximately
these three formations.
Now here's the kicker.
A group of paleontologists,
including [INAUDIBLE]
and others, showed in 2011
that if you go and look
at drill cores-- you
people can't see this.
Over here, in the Bay of
Bengal, where these lava flows
cap Cretaceous sediments,
that those lava
flows come in exactly at the
Cretaceous-Tertiary boundary.
So we've gone from a small
problem to a huge problem.
The small problem
is-- well, number one,
why does the K-T boundary have
an impact and a flood basalt?
Given that the flood
basalts typically--
they're main phase of eruptions
only last 1 to 2 million years,
what are the chances that the
largest Phanerozoic crater
we have happened during
that period of time?
But now it's a lot worse because
the amount of time separating
the K-T boundary and the
onset of these three huge lava
sequences is probably
less than 100,000 years.
And the chances
of that happening
at random,
geologically speaking,
are about 0, or
actually, 1 in 100.
But, you know, we
can round off to 0.
And we know that the
Chicxulub impact did not
cause the volcanism because
it was well underway here
as a general event
long before the impact.
And of course we know
that the volcanism
didn't cause the impact.
That would be really
quite unthinkable.
But the hypothesis
is as follows--
this is an image of one of those
big, hot blobs of corn syrup
but scaled to the thermal
convection in the Earth's
mantle of hot stuff
from the core mantle
boundary or the
lower mantle region
coming up and making a big
pancake underneath the earth's
crust and lithosphere.
And this stuff cooks a while.
It forms into
veins and channels.
It sits at the crust
mantle boundary here
we call Moho and drops out some
heavy minerals as it cools.
And then it erupts the Deccan
Traps or a large igneous
province.
This is the canonical--
or this is the paradigm
for how large igneous provinces
form according to this plume
head and tail theory.
Now imagine this.
You've got this region here.
It's about 50 to
100 kilometers thick
and about 1,000 kilometers wide.
It is saturated with
partial melt, that
is if you add a small
amount of partial melt
or you make that melt become a
little bit more interconnected,
it's going to come
squirting out.
And that's basically what
causes periodic eruptions.
You hit the Earth with
a magnitude 11 or larger
earthquake.
You pass Rayleigh
waves, or surface waves,
through this region that
have meters of displacement,
and you get some kind of
physical effect probably
that may be something
like liquefaction of sand
when you have
earthquakes, which we do,
in the San Francisco Bay Area.
It's not difficult to imagine
that perturbing a system
this massive with this
large a disturbance
might result in
something anomalous.
And so our idea is that
these extraordinary lava
flows within the Deccan Traps
were triggered by this event.
Now to give you a good analogy
for how to think about this,
this isn't that
unusual in nature.
This is a photograph
from the San Francisco
earthquake in 1906.
And anybody who knows much about
the San Francisco earthquake
knows that it was only about
a 7.8 magnitude earthquake.
It wasn't that huge.
It was very destructive.
It destroyed most of the
city of San Francisco.
But the main reason it destroyed
the city of San Francisco
was because of the fires and not
from the strong ground motion.
So that's what I would call
a major secondary effect.
And of course, for
the Deccan Traps,
the secondary affect-- the
question you want to ask then,
was it the impact
and the fallout
from the impact that
killed the dinosaurs
or was it the volcanism that
caused the extinction boundary?
Because we know
that volcanism is
associated with the other three
major extinction boundaries
since 250 million years ago.
Now I'm going to warn you
before I put up the next slide.
This is a horrendously
complicated slide.
It represents a huge amount
of geological information
all at once, and
I don't want you
to get dizzy when you see it.
But the reason I'm
going to show it to you
is that I'm going
to come back to it
at the end of the talk with some
new data that will be much more
comprehensible.
But I want to give
you a flavor for what
it is that we've been up to.
There are people
in this room that
know more about some
of this than I do,
so I will excuse myself.
But here again, we see this
stack of Deccan formations.
You'll recognize these names.
OK.
And there are three different
data sets represented here.
And I'm going to tell
you what they say
without explaining them to you.
This data set here says that
at the Bushe-Poladpur boundary
or the onset of
the Wai subgroup,
the chemistry as reflected
in isotopes of neodymium
and strontium tells you that
this stuff is coming right out
of the mantle with no time
to interact with the crust.
These diagrams over here on
the right show that at the time
these eruptions were initiated,
the stress system governing
the fractures in the
crust that were feeding
these eruptions became randomly
oriented, which means that they
probably resulted from huge
magma overpressure in the crust
rather than regional
processes of extension that
may have been going on when
these formations were happening
down here.
All of this indicates
that effectively someone
turned on the hose
from the mantle very,
very quickly with this partial
melt flood literally coming out
from an ongoing set of
eruptions that had otherwise
been percolating along
at a rather modest rate.
In the middle column--
I'm going to ask
you to strain your
eyes-- what we have here
is time on this axis
up here from 64,
say to 70 million years.
This dash line falls
along the K-T boundary.
We know that's at
66 million years.
And these are the age
ranges as determined
by previously published
radiometric ages
on these formations.
The thing you should take away
from this is this is horrible.
These ages had huge error
bars, and they're worthless.
They tell you almost
nothing with precision
of what we need to know about
what happened in this lava
stack relative to
the K-T boundary.
Because we know, in
fact, all these lavas
came out within a million
years of this boundary,
certainly between 65 and 67.
And these are all over the map.
So the essential
scientific problem
and challenge of trying to nail
down what actually happened
at the K-T boundary, what
killed the dinosaurs, what's
the relationship between
the impact and the volcanism
comes down to primarily
uranium-lead and argon-argon
geochronology with
mass spectrometers.
So time for a road trip.
The sampling of the Deccan
Traps have been very haphazard
in the past.
And so this is Mumbai Harbor.
My colleagues, Steve Self, Paul
Renne, geochronologist, myself,
and Paul's student,
Courtney Sprain
took a trip to India last March.
And we had a lot of fun.
Our first visit was to-- anybody
ever been to Elephanta Island
in Mumbai Harbor?
It's a national park.
And the reason it's
a national park
is that the medieval Hindus
carved these lovely stone
temples into the lava
flows of the Deccan Traps.
And here is Steve Self,
the volcanologist.
This tourist is looking
at Vishnu over here.
Steve is looking at the
lava flow crust tops.
These are actually
lava flow tops.
And there's a lava
flow top right here
that goes through Vishnu's mouth
and comes right through here.
And you can see the structure
of these individual lava
flows just beautifully.
Now that wasn't the main show.
The main show was the Deccan
Traps, the large sequences
that you see, that dominate
this entire landscape
in northeastern India.
They're called
the Western Ghats.
Ghats is a Hindu term
referring to steps
leading up to the Hindu
temples of medieval times.
And you can see that
these lava flows--
these are individual lava
flows that are, of course,
colossal in extent
and thickness.
They lead to a
step-like topography.
Has anybody ever traveled
in this region of India?
Now you know what it was
that you were looking at.
Yeah.
So it's very entertaining to
travel on these extremely steep
mountain roads with every
conceivable kind of vehicle
coming at you.
This is a very hazardous
form of field geology.
And I just never
cease to be amazed
at the ingenuity of Indians
and the various vehicles
that they manage to navigate
the various roads with.
And we always had the friendly
combination temple and chai
stop to keep us awake
during our field travels.
These are the famous
strawberry arrangements
of the town of Mahabaleshwar
for which the Mahabaleshwar
Formation is named.
And it's just a lovely,
lovely part of India.
And we had a wonderful time.
These are the langur monkeys
with the Deccan Traps behind.
And perhaps these
monkeys are saying,
you know, if it weren't
for these rocks behind me,
you might be looking down
the throat of a T. rex
at this point.
But getting down to business, we
were there to look at the rocks
and sample them.
This is about 20
meters tall, I believe.
And this is a single lava flow.
Some of these lava flows reach
thicknesses of 50 to 70 meters.
This is in the Ambenali
Formation, these huge sheets
of lava that spread across the
entire Indian subcontinent.
And this is called
sigmoidal joining.
This forms as fractures
after the lava is cooling.
And of course, what
we were really there
for was to sample the rocks.
This is Paul Renne,
geochronologist
swinging his very large rock
hammer at these poor rocks
and trying to get samples
that were specifically
tailored in nature to doing
high precision geochronology.
And this is Paul looking
at another formation that
turned out to be really run.
And this is another
shaggy dog story coming.
This is called a red bull.
It's a term that the
Indians use to describe
soil horizons,
that is weathering
horizons between lava flows.
So this is an upper lava flow.
And down here below,
which you can't see,
is another lava flow.
So the time interval between
these massive lava flows
is probably substantial,
perhaps of order 5,000
to 10,000 years separating
each individual lava flow.
And these weathering
horizons are
very interesting for
a variety of reasons
because they do give you
some sense of time elapsed.
So this is [INAUDIBLE],
one of the people
who went in the field
with us as well,
holding a much less macho
hammer here next to one
of these red bulls.
It wasn't actually red.
But this is still a weathering
horizon between two major lava
flows.
Now this particular
contact happens
to be at the boundary that is
the lower boundary of the Wai
subgroup lava flows, the
lava flows that come out
and cover a good bit of India.
Or it's called the boundary
between the Bushe Formation
and the Poladpur Formation.
And I looked out across
the horizon the other way,
literally from where I was
standing taking that picture,
and I noticed
something interesting.
And that is that the entire
landscape from this point
is dominated by these horizontal
bench structures, or terraces,
that correspond to the same
topographical level for as far
as the eye can see.
And this is what it looks like.
Oh, this picture's
a little fuzzy.
I'm going to show you a
better image in a minute.
This is standing up on
top of the Ambenali flows,
the largest lava flows
known on the planet,
looking down at these terraces.
There's one terrace horizon,
another terrace horizon,
and one back here
that you can hardly
see because the
picture's little blurry.
This is a very clear day in this
part of India unfortunately.
It turns out that this is
a bit of a smoking gun.
It's a bad joke, actually.
But it turns out that these
terraces are very, very
interesting, more interesting
than I would ever imagine.
I came back to Berkeley
after this field trip,
and I showed these photos
to Walter Alvarez saying,
Walter, what the heck is this?
He said, I don't have any idea.
Let's get on Google
Earth and have a look.
Google Earth turns out to be,
of course, a real research tool
these days.
And this is a view
using satellite images
and the tilting up perspective
capability of Google Earth
that Walter showed me.
And this is effectively standing
pretty much in the same spot.
And again, you see
these terraces.
These are agricultural
terraces built
on the topographic
terraces going
as far as the eye
can see, dominating
this part of the landscape.
About two days later-- and I was
literally out in the backyard
throwing footballs
with my son, which
is kind of a sacred thing to
do for those of you who've
done that.
And Walter calls me up.
Actually, my wife comes out
and says, Mark, Walter Alvarez
is on the phone.
And I said, well, can
I call him back later?
I'm playing football with Noah.
And Sarah goes back in.
And then she comes
back out and says,
no, Walter says he needs
to talk to you now.
And so I go, and
I talk to Walter.
And Walter says, Mark, there's
something I need to show you.
And I said, well, can
I come over tomorrow?
He said, no, you need
to come over right now.
Now when you're
working on problems
that involve the K-T
boundary and Walter Alvarez
calls you up on a Sunday
afternoon and says,
you need to come
over right now, you
need to come over right now.
And this is what
he had to show me.
He was looking at
aerial photos again
through Google
Earth to the north
several hundred kilometers
from the site that I just
showed you, seeing the
same terraces dominating
the landscape.
And this has never
been published or noted
in the literature
that we're aware of.
And it's kind of amazing.
But he said, Mark,
look carefully at this.
Look and see what you see.
How good a geologist
are you really?
I said, Walter,
I'm a geophysicist.
You know?
Give me a break.
He said, look at
these fractures.
Now these are fractures that
occur below the terrace level,
and they're pervasive
throughout the landscape
until you hit this
terrace level here.
They stop.
Now this is the next
image he showed me.
He said, look, on this high-res
image from Bing Images,
you can really see
these fractures.
And these terraces
from above that
are labeled PB-- that's for
Poladpur-Bushe boundary--
do not have these fractures.
The fractures stop
stratigraphically
at that level.
And then he said, look
at this fault over here.
Here's a close up of that fault.
That fault runs right up through
all these other fractures,
through these lower
formations, and it
stops dead at the
Bushe-Poladpur boundary.
Now what does this
mean to a geologist?
It means to geologist
that there's missing time.
Because stratigraphically,
what had to have happened
is that these fractures
and faults had
to have taken place
and then the lava
flows came in on top of them.
Something really
significant happened here.
Well, that just adds to the mix.
We know that the stress
system changed at this point.
We know that the geochemistry
changed at this point.
We know that the
volume of eruption,
or the rate of effusion,
increased by, perhaps,
an order of magnitude.
And now we know
that there was also
a break in time, which suggests
that the Deccan Traps were kind
of yawning and saying,
well, maybe we're done,
and then something happened.
We still don't know
exactly what this means.
But it means that
there is a major break
in the character of what
happened in the Deccan Traps
at this point.
So Walter's wife, Millie,
snapped this photo of me,
which I will always treasure.
And I have to say that
it made me very happy
that 25 years ago, when
I came to Berkeley,
I very decidedly
did not take sides
in this volcanic
versus impact debate.
Because Walter and I have
remained great friends
through all of this as a result.
But back to the real business.
These are the sample bags
that Paul Renne and I
were bringing back from the
Deccan Traps and Kanchan
Pande's lab at the Indian
Institute of Technology.
Now if you've ever tried
to ship 600 pounds of rock
from Mumbai to the United
States in the post 9/11 era,
it took a lot of creativity
on Kanchan Pande's part
to figure out how we were
going to justify this.
But we did get the rocks back.
And the purpose
of these rocks is
to do very high resolution
mass spectrometry geochronology
looking at the potassium-argon
decay scheme, which
can give such high precision.
And now, I'm going to show
you the initial results
of that work, which literally
are only two weeks old.
First of all, this is back
to this horrendous figure
that I promised you I
was going to explain.
And now I'm going to
pare it down to size
so your eyes are hopefully used
to this stratigraphic column.
Time starts here.
It goes up this way.
This is about a million
years elapsed time.
The big event starts here at
the bottom of the Wai subgroup
flows, the Poladpur,
the Ambenali,
and the Mahabaleshwar.
Blair Schoene, and Gerta
Keller, and Sam Bowring
at MIT and Princeton just
published a paper in Science
with these two dots
that are actually
a little bit larger than the
actual error bars of precision
on the measurements of
uranium-thorium dates
on minerals called zircons
that are in the red bulls
and the soils between these
lava flows for the Mahabaleshwar
and the Ambenali formation.
These are just discernibly
older than the K-T boundary.
Just after.
Paul Renne's recent dates--
now, this green dot down here
is probably problematic.
And I'm not going
to discuss that,
but it's not to
trusted at this point.
And neither is this red one here
that Paul Renne just produced.
But these are very good ages
that Paul Renne's lab just
produced in the lower formations
because these are the first two
dates that have come out.
Now the hypothesis that
we've been suggesting
is that this boundary
between the Poladpur
and the Bushe, that
terrace-forming boundary where
all hell breaks loose
in the geochemistry,
and the tectonic signal,
and the amount of lava
should fall right, of
course, at the K-T boundary
at 66 million years.
And this is something
I would never
do with this scant of
data in a published work,
but since this is
a public forum,
you're tempted to draw
a line through these.
And if you draw a line
through those data,
it looks pretty darn good.
And we just found this
out a couple weeks ago.
So what have we learned?
I would call this a
hypothesis of reconciliation.
And again, I want to repeat
what I said at the beginning.
Everything I've told you
may turn out to be wrong.
And that would be OK with me
because the way that science
is supposed to work is
that when you go out
to test these ideas with
a higher precision lens,
you find out what
really happened.
And so far, since
that hasn't been done,
we're going to understand
this a lot better
no matter what the actual
causative relationships might
be.
And that's a beautiful thing.
But it's a hypotheses
of reconciliation
with no alternative.
There is-- I know of no
other suggested alternative
explanation for why the
very largest eruptions
within the Deccan Traps by a
long shot, the K-T extinction
boundary, and the
Chicxulub impact
should all have occurred within
100,000 years of each other.
So I'm going to go
with it for now.
If this coincidence is
difficult to dismiss,
if seismic waves from
Chicxulub impact--
it is likely that
they were large enough
to trigger volcanism worldwide.
And that leads to all sorts of
other things we can go look at.
For example, the
mid-ocean ridge system
should also have been triggered
into extraordinary activity
at the time.
The signal from that may
be difficult to detect,
but I never cease to be
amazed in this journey so far.
And we haven't tried that yet.
If, of course, the Chicxulub
impact triggered the largest
Deccan Traps eruptions,
then clearly,
the Deccan Traps
may have contributed
to the extinction itself
in addition to the impact.
Now my paleontologist
friends tell me
that no known taxa in the
paleontological record
disappeared after
the iridium anomaly.
So I'm very skeptical still.
I remain very skeptical-- I
want to be clear about this--
of the idea that anything
other than the impact
was the main causative agent
of the K-T extinctions.
But I'm a geophysicist, and if
a magnitude 11 impact triggered
the largest volcanic
eruptions that we
know of in the last
250 million years,
that's a pretty cool
geophysical event.
And that's going to
lead to a lot of work
no matter what
its relation might
be to the extinction boundary.
And the punchline
here is that the best
kind of hypothesis or theory
is one that you can test.
It turns out that
this hypothesis
is one that's probably a
lot easier to prove wrong
than it is to prove right.
If we found another smoking
gun like an extraordinary pulse
of activity at the mid-ocean
ridges or arc volcanoes
or something else that we
haven't thought of yet, fine.
But we haven't
thought of that yet.
But if, for example, we showed
that, in fact, this major phase
of volcanism actually started
before the impact, then
that would through a lot
of water on the idea.
So far, the geochronology
looks like it actually
isn't perfectly in line
with what we have predicted.
So it's a little epilogue
here just to kind of drive
the point home at
just how much fun
you can have when
you're a scientist.
On our last day at the Indian
Institute of Technology
in Mumbai, Kanchan Pande
went to his file cabinet
and dragged out this
manuscript that kind of
had the appearance of
finding the Dead Sea
Scrolls although it was
only published in 1986.
And it's a well-known paper
by a group from Beane et al.
who did the chemical
stratigraphy
of the Deccan Traps.
And he pointed out to
me a simple sentence
that you will not
understand, but which
I will translate for you.
In this paper, it says, "On
the southern end of the Western
Ghats south of
Mahad--" which is where
we were working
in Mahabaleshwar--
"analyzed samples of drill
core from [INAUDIBLE]."
The reference is an
unpublished PhD thesis
of John Mahoney in 1984.
"Placed the base of
the Bushe Formation
at 450 meters below sea level."
What this means is that
there are drill cores that
go through the Bushe-Poladpur
boundary that are probably
sitting around in
warehouses in India.
And in fact, we are in contact
with one of the hydrologists
who works with these cores.
He's a volcanologist
turned hydrologist
at the University of Pune.
A year ago, if somebody had told
me that we might know within
a meter or two where are the
actual K-T impact iridium
anomaly might be within the
3,500-meter stack of the Deccan
Traps I would have
laughed at that idea.
But now, at that terrace
level, within a few meters
plus or minus, is our best bet
for where that might be found.
And so we are going to soon
be on a hunt for the archives
of the hydrological agencies
in this region of India
to try to find intact
core samples that
can be run for analysis and
see if that would get me
another smoking gun or at
least a very strong indicator
of exactly where
the impact occurred
in this massive stack of lavas.
So this is a fun field
to be involved in.
If I have left you
with the impression
that we know the answer
to this question,
I have failed utterly.
But I hope I've left
you with the impression
that this is a grand adventure,
that a great deal of humility
is called for, but
that in next few years,
we're going to make
a lot of progress.
Thank you very much.
[APPLAUSE]
So I think I'm allowed
to answer questions.
Yes, sir?
AUDIENCE: [INAUDIBLE] Between
five and three years ago, I
started teaching a
course and looked
into this question of what
killed off the dinosaurs.
It occurred to me
that the Deccan Traps
are almost antipodal--
MARK RICHARDS: They're not.
AUDIENCE: --to Chicxulub.
Not quite, but close,
and tracing back
65 million years ago
wasn't exact either.
But it occurred to me, still,
that the seismic energy created
by that impact would have
gone around the globe
and concentrated
near the Deccan Traps
and perhaps set off the
Deccan Traps at that point.
MARK RICHARDS: Well, that theory
was actually published very
shortly after the evidence--
AUDIENCE: I didn't
finish my question.
MARK RICHARDS: Oh, excuse me.
AUDIENCE: Sorry to
be so long-winded.
MARK RICHARDS: OK.
AUDIENCE: But anyway, I
was intrigued by this,
so I went to some
geophysicist friends.
And they said, oh, that
was thought of long ago
and it was worked
out mathematically.
There's no question that
that couldn't have worked.
So I was wondering--
because I didn't follow up--
who wrote that paper?
And what holes there might be.
MARK RICHARDS: Yeah, yeah.
Well, no.
It's a very good question.
And it helps me clarify
some of the subtlety of this
because there is a
history to this problem.
Shortly after the
evidence for the impact
was discovered in 1980, it was
proposed by a number of people
that perhaps the
antipodal-- when
you have a seismic wave,
an earthquake on one
side of the planet,
the waves travel
around the planet, the surface
waves and the body waves,
and they coalesce at the
antipode 180 degrees away.
And you get a maximum amplitude
in the far field from that.
So because we knew that the
Deccan Traps were going off
roughly at the same
time of the impact,
people said, oh, Deccan Traps.
Maybe they were antipodal
to the impact site.
Because we didn't know
where the impact site was.
When the impact
site was discovered,
it was discovered 130 degrees
away from the reconstruction
for the Deccan, which is
well within the error bars.
It is clear that it was
not at the antipode.
So that idea went away.
And furthermore, the people
who do cratering studies
and looked at the
energy said, that
is not nearly enough
energy even if you did
have antipodal focusing
to melt the mantle
to produce that amount of lava.
The difference
between our hypothesis
is therefore two-fold.
One is you don't have
to be at the antipode.
And secondly, you don't
need that much energy.
[INTERPOSING VOICES]
Because all you have
to do is trigger
the melt that's already there.
And to change, effectively,
the permeability of the system
not that much to
create instabilities
and channelization of melt
to get this outpouring.
And that's what--
it's odd to me.
Other people may have
thought of this idea,
but it hasn't been
published before.
When I came up with this
thought, the first thing I did
is say, OK, somebody
else has done this.
I scramble, look
through the literature.
But this seems to escaped
people as a causative mechanism.
So it's a very,
very good question.
Yeah?
AUDIENCE: As a
result of all this,
what made the
dinosaurs [INAUDIBLE]
starvation or darkness
around the Earth with no sun?
MARK RICHARDS: Well.
This is where I get repeat again
that I'm not a paleontologist
and there's a lot of
controversy about this.
Unfortunately, the impact
scenario and volcanism scenario
do some of the same things.
The Chicxulub impact
hit a carbonate shelf,
which releases a lot of
carbon dioxide and sulfur
into the atmosphere.
The killer agent with
the Siberian Traps
is thought to be because that
mantle plume volcanism came
through a carbonate and
evaporite stack of 1,000 meters
or so of sediments
that were very
carbonate and sulfide laden.
And so launching sulfur
into the atmosphere
create sulfate aerosols, the
acid rain, global cooling
event.
But it gets out of the
atmosphere pretty quickly even
if you get it into the
stratosphere, which
is hard enough.
Carbon dioxide,
on the other hand,
has several hundred year
cycle, maybe 1,000 year cycle,
for getting it out.
And so you could
see a one-two punch
with global cooling
followed by a longer
period of global warming.
There's has been endless
speculation on the-- people
obviously pay a lot of
attention to the pattern
of species extinctions.
For example, those
foraminifera that I showed you
in that original rock
from Walter Alvarez,
those are planktic foraminifera.
They live in the shallow water.
The benthic foraminifera that
lived at the base of the ocean
hardly noticed the K-T boundary.
So there is a lot
of work on this.
And I could try to repeat some
of the arguments I've heard.
And I would simply be
creating the opportunity
to lead you astray.
There's a vast literature,
and it's unsolved.
It's unresolved problem.
Yeah?
AUDIENCE: In the
stratigraphic diagram
you showed, the line [INAUDIBLE]
points, is the interesting part
that it's almost vertical?
MARK RICHARDS: No,
the interesting part
is it goes through
that blue star, which
is where we would predict--
AUDIENCE: I'm sorry.
I don't understand
the point to it.
MARK RICHARDS: Yeah.
OK.
Good.
I'm sure that
other people didn't
understand that point as well.
The hypothesis is
that at the time
that this Wai subgroup,
this outburst of lava,
came as a result of the K-T
impact at 66 million years.
So the intersection of this
contact boundary and K-T time
is this blue star.
So the prediction
is that if you were
to get-- when we get the dates
for all these other formations,
that they will presumably
fall on a line roughly
through this point, so
that this stuff is younger,
and this stuff is
just a little younger,
and this stuff is just
a little bit older
than the K-T boundary.
So I am almost sorry I
drew that line on there.
Like I said, I would never
publish something like that.
But I wanted, basically, to try
to illustrate what, obviously,
I didn't explain very well.
So thank you for
asking the question.
Yeah?
AUDIENCE: I have two
examples of earthquakes
being caused by perhaps
non-antipodal explosive events.
One recently occuring
[INAUDIBLE], which they say
was a result of
fracking, [INAUDIBLE].
That in the fracking process,
they do these explosions
to [INAUDIBLE] correlation
between [INAUDIBLE] picking up
several hundreds miles
away, not [INAUDIBLE].
And then the other [INAUDIBLE]
is bombing in Baghdad,.
There was a relatively
minor earthquake
that occurred along the
Appalachian Trail that
started on [INAUDIBLE]
and went all the way
down the Appalachian
Trail, about 3.2 magnitude.
[INAUDIBLE] backed up and hit
Canada and the [INAUDIBLE]
MARK RICHARDS: OK.
I will make a very
strong statement,
which is the energy of
the bombing of Baghdad
could not have induced
earthquakes around the globe.
There are many, many other
events larger and closer that
would have done it instead.
So that's probably not your--
AUDIENCE: Well, to me,
there's a correlation.
MARK RICHARDS:
Well, correlations
are things we have to be
very careful with in geology
because we tend to find
things we're looking for.
Somebody else?
Yeah?
AUDIENCE: I read a few years
ago about [INAUDIBLE] craters
around the Permian-Triassic
extinction.
Any comment or any--
MARK RICHARDS: I don't know of
any large craters at that time.
AUDIENCE: OK.
I think there was
information published
in Science. [INAUDIBLE] but they
were dated to roughly that time
period.
MARK RICHARDS: There have been
some published suggestions
of what are called microtektites
in the Permian-Triassic
section.
They have been hotly contested.
I don't know of any large
craters, certainly not
anything like as
large as Chicxulub
associated with
Permian-Triassic time.
Yes, sir?
AUDIENCE: Can you say a
little more why you're
dismissing the 2.2 [INAUDIBLE]?
MARK RICHARDS: Yeah, Paul
doesn't like this date
very much.
And I'm not sure exactly
why, but I tend to trust him.
This date is on what is called
a melt segregation feature.
And it's hard to
understand how it also
contains zircons that have
Precambrian ages in them
as well.
It's hard to understand how
you drag Precambrian zircons up
in a large lava flow
without dissolving them
and preserve them.
And so this may be a
sill or an intrusion
that comes after the fact.
And so this age
maybe a little young.
But I think Sam Bowring
and Blair Schoene may
argue with me on that point.
And so I'm just a little bit--
I'm not discounting this age.
It may actually be right.
And if it's right, it
doesn't disprove anything
because there's a
lot more to go here.
But that's why I'm a little
cautious about that one.
Yeah?
[INTERPOSING VOICES]
Go ahead.
AUDIENCE: Vincent
Courtillot, I noticed,
was the co-author
with you in 1989.
MARK RICHARDS: Yes.
AUDIENCE: And I know that
through a number of years now,
he has been pushing the idea
that the Deccan Traps were
the real cause of
the extinction.
MARK RICHARDS: Yes.
AUDIENCE: And as I
recall the argument, one
of the things he had
to establish in order
to make that a reasonable
hypothesis, because he had
the gases released
doing the killing,
that is from the
Deccan Traps, that it
has to be released in a
short enough period of time.
And the difficulty was
in making estimates
of the time period
of those eruptions
with a small enough error
bar, like tens of thousands
of years.
MARK RICHARDS: Yes, yes.
AUDIENCE: And he wasn't
anywhere near that.
MARK RICHARDS: That's correct.
AUDIENCE: What is
his status now,
and how does he react
to your [INAUDIBLE].
MARK RICHARDS: Well, Vincent
Courtillot was a good friend.
And I disagree with him
vehemently about the evidence
that he cites for-- you
know, he's trying to suggest,
for example, that these
entire formations might
have been erupted in
a few thousand years.
And the fact that there
are well-developed soil
horizons between individual
flows pretty much
makes a nonstarter.
What he is correct about is
that from Mahabaleshwar time
to Jawhar time
represents probably
an order of 600,000
or 700,000 years.
As you say, that's not
nearly quick enough
to do the environmental
damage that he's after.
Yes, sir?
AUDIENCE: Are zircons
ubiquitous in these formations,
so you'll be able to
gets dates [INAUDIBLE]
MARK RICHARDS: I'm the
wrong person to ask.
You generally don't
find good ones
in lava flows, which is why
the argon-argon method-- if you
actually want to know
how old the lava flow is,
it's good to use
argon-argon methods.
The zircons from
these two dots are
zircons that are deposited in
the soil horizons between lava
flows.
And there's an inference.
In fact, there's a
whole spectrum of ages.
And you just take
whatever the youngest one
is, is the maximum possible
age for that formation.
So it's good to have both.
It will be good to have
both of these data sets.
And we have three
to five samples
for each one of
these formations.
They're going to be a lot
of red dots on this diagram.
And the width of
this dot right here
is the two-sigma
precision of the method.
And so it's going to improve
vastly in the next six months.
And we might be right.
We might be wrong.
Yeah?
AUDIENCE: Is there
no correlation
between known meteorite impact
[INAUDIBLE] recorded history
and increased volcanism?
MARK RICHARDS: Oh,
people have looked--
the question is, is there a
correlation between impact
crater occurrence and
large-scale volcanism.
And that has been
looked for extensively.
And there's no correlation
that I know of.
And that is from the people
who would like to find one.
AUDIENCE: So for this
hypothesis to work,
it would have to be something--
just because it's unusally
large--
MARK RICHARDS: This
is a one off event.
AUDIENCE: Right.
MARK RICHARDS: Yeah.
AUDIENCE: So like
the one in Arizona--
MARK RICHARDS:
There's no evidence
for impact at any other
major flood basalt event
that we know of.
AUDIENCE: OK.
PRESENTER: Well, thank
you all for coming.
We could ask him
questions all night,
but I want to take him
off to get some food.
[APPLAUSE]
