hi everyone it's mr. sin T and today I'd
like to kick around the idea of the
fossil record yeah I hope this
conversation will provide some interest
to you I think the fossil record first
thing I kind of want to say about it is
that it's been such an important source
of evidence for organisms changing on
the planet Earth it's it's remarkable
how it's been a chronology of the life
history of organisms not just recent
times but millions of years ago we're
able to go back sort of like looking at
the annual rings of a tree we're able to
go back in time old newspapers if you
will and sort of uncover some of the
great organisms that have lived in the
past that no longer lived today there
are sort of the the biological
historical documents of our of our time
and so one of the things that I want to
say about this is that the fossil record
in in terms of evolutionary biology is
both you know a process evolutionary
biology is a process in other words like
natural selection preferential
reproduction between different
variations and a population reproductive
success and then speciation in history
so all of this is combined and we can
see this occurring in the fossil record
it's pretty pretty awesome so I want to
start off by introducing you to or maybe
not introducing but reacquainting you
with this sort of fish called the
stickleback and it has these dorsal fins
that are kind of spiky which allow it to
you know not necessarily resist being
caught by a predator but predators don't
seem to enjoy getting poked by these
these fins but biologists have been
interested in these sticklebacks forces
for several decades and it's because you
can see here there's evidence that their
marine form of a stickleback mode
stickleback is it's capable sort of like
a salmon of
living in the salt water and the fresh
water and the marine version is heavily
armored with these plates which prevent
it from being you know tune up by like
toothed predators in the ocean but when
you look at freshwater versions of this
lake that have the freshwater versions
of this fish that have been isolated in
lakes for several thousands of years you
could see that they've given away their
heavy armor for being a little bit
faster and they have reduced dorsal fins
and so what's interesting is that
natural selection because the predator
and some of these natural lakes are
these dragon fly larvae that like to
hold on to those dorsal fins and so if
you're a stickleback fish and live in
the lake you have a better chance of
surviving a differential reproductive
success having more offspring if you
have reduced so we could see natural
selection in process occurring and
what's totally cool about this is that
it's led us to the understanding that
some of these sticklebacks in different
lakes are actually different species is
about 40 different species of you
depending on where you are if you're
studying these like for example some of
the lakes in Canada and around Vancouver
or if you're up in Alaska studying these
pretty pretty cool example of adaptive
radiation so the generation of whole new
species based on the fact that maybe
they don't you know they're isolated at
different legs but even if you bring
them together they don't reproduce with
one another behaviorally so they don't
really females don't choose to mate with
some of the males that are that are
different and a parents kind of
interesting so we can actually see the
the result of natural selection so
microevolution changing phenotype in a
in a population resulting in macro
evolution or this new species over time
and what's totally remarkable about this
and what this is what the the heart of
what this video is really about is that
we have evidence in the fossil record
of the stickleback fish that have been
preserved and we can see whatever
various traits that were considering we
can look at the dorsal fin and we can
look at the hind fin and actually see
how these changes in phenotype have been
occurring historically in the past as
well given the varying environmental
conditions that our earth is infamous
for and so the fossil record pretty cool
but you know Charles Darwin wasn't the
very first person to think that life
that's been changing over time sometimes
he's given that that credit other
naturalist were familiar with life has
been changing in the fossil record in
evolving Charles Darwin just gave us the
mechanism that is of natural selection
so the the fossil record is a record of
change and so this is an important
statement and so when you look at like
this is a great example of fossils here
in the Grand Canyon in Arizona in the
United States where you can see layers
and layers of sedimentary rock formed by
the erosion of this Canyon by the
Colorado River and what we see in the
fossil record is that fossil fish which
which are a little bit lower in the
fossil record predate land vertebrates
which are up here which then predate and
Vivian's which are up here and then next
followed by reptiles that are here and
then mammals that are up here so it's
like going back in time looking at
fossil records it's like layers upon
layers of sediment have preserved these
organisms and you can sort of go back
and look at the history of life changing
on the earth now just to acknowledge the
fact that a creationist perspective
might be that life was all created and
when one particular time and that is not
what the paleontologists actually
observed when they go back in the fossil
record just wanted to acknowledge that
and so the major goal of evolutionary
biology is to sort of reconstruct it's
like not necessarily it will be dramatic
as a crime scene where you're training
reconstruct the city the city the scene
from something that happened the past
but kind of like that you're going back
in time and searching and trying to
reconstruct what life was like before we
were around to observe it and select I
was mentioning the stickleback you could
look at things for example if you could
spine this in the fossil record you
could look at the fact whether or not it
had a complete pelvic area and and a
really pronounced hind fin or whether or
not it was reduced and then you can sort
of come to conclusions about what were
the environmental conditions favoring
that so it's going back and looking at
life's history through the fossil
records and why are we interested in
that for a variety of reasons but one of
them is systematics which is just this
biological study of the diversity of
life on this planet in an evolutionary
context and what I mean by that is
biologists like to look at different
species and try to understand their
relationship to one another so they're
they're Fulani in other words their
evolutionary history as a species as it
relates to another species so we could
say if we're staying with the
stickleback we could say that one
species of stickleback ceases one is
more closely related to species two than
it is three and that what we can draw
this phylogenetic tree and then see that
this lineage of species - in the species
one right in this area these fish were
the common ancestry - and ancestors to
both these species and then if you go
back in time this area right here these
fossils were perhaps the ancestors of
both three two and one so this is the
common ancestor so you can you can
create these phylogenetic trees if you
will to understand evolutionary history
through the fossils pretty cool and so
fossils just to establish what they are
they're basically preserved remnants or
impressions left by the organism in the
past and so as I mentioned before
they're sort of the historical documents
of biology and what's particularly cool
about fossils many things is that
they're ordered there's an ordered array
that appears in the sediments like for
example in a drive lake bed in Nevada
United States you can see that in
certain areas there's layers upon layers
of sediments of diatoms that have have
died in the past and have settled and
informed this the strata and you can
literally go back and look at this and
excavate at in this quarry if you will
and actually look at the time we'll talk
a little bit about how time is as
measured in terms of rock and in organic
molecules in the fossil but you can
literally go back in time and say that
at this particular of strata this is
what was happening it had a complete
hind fin and then and back here it had a
reduced hind fin so it's pretty awesome
and pretty powerful the fossil record
and again the the sediments this might
be a basic idea but basically the
sediments formed in water the silt
settled to the bottom and then when an
organism dies obviously it it settles to
the bottom and those deposits pile up
and compress older sediments and so you
can basically go back and these are the
oldest ones right here and these are the
newest ones okay up here so these are
the old sediments and new ones and
eventually rock will form and thus it's
called sedimentary rock and it's the
richest source of where we can find
fossils but there's other places where
you can find fossils and so these bodies
of dead organisms settled with the
sediments you know the truth is only a
tiny of the fraction of the organisms
actually I've become preserved as a
fossil and that again might be obvious
some of the soft tissues some of the fat
and the some of the muscle and things
like that are obviously going to
decompose the things that are a little
bit hard things that are like bony for
example are more likely to preserve and
so there are certain places that are
that are famous and there's actually
national
parks a favorite is Dinosaur National
Park here and kids is absolutely loved
and I think everyone the kid and
everyone loves a dinosaur and so
incredible
organisms that lived millions of years
ago and you can find them the hard parts
of them in other words the bones and
teeth and shell that remain preserved
for again millions of years pretty
awesome what's interesting is it's
sometime under the right conditions that
sometimes minerals will in dissolved in
the groundwater will actually seep into
the tissue of the dead organism and it
actually replaces some of the organic
material and it forms a cast and
fossilized the them and petrified them
in tune so you can actually see a bone
structure that is more rock than it is
bone from that organism and then other
cool examples even more rare are these
mineralized fossils that that retain
organic material and that they're
they're found in like in between the
layers of sandstone and shale like you'd
have to go in there and one of the great
sites is this burgess shale up in Canada
you go in there with your pick you're a
paleontologist and you're just
fracturing these like sheets of shale
and you can open them up and it's like
wow you can see these incredible
fossilized films if you will of
organisms that live back in the cambian
age remarkable kids see the eye and and
some of the tentacle structures and some
of the leg structures pretty pretty
impressive and so even more rare you can
find impressions of leaves which again
are kind of soft tissue and even some of
them are even slightly green Wow
containing a little bit of chlorophyll
but probably in terms of you know plants
you're looking more at like preserved
pollen which is kind of a little bit
more sturdy and will survive
decomposition and aggregation over time
another cool thing about fossils is
trace fossils you can actually find
footprints how interestingly is this or
burrowing sites
impressions left in the sediments by the
activity of animals so you know in what
what can a footprint tell you can tell
you a lot can tell you about I mean I'm
not an expert paleontologist by any
means but it can tell you about the gait
of the organism how fast it's capable of
that weight it can tell you a lot about
a particular organism and what it was
what it was doing and how it was how it
was hanging out what it would have it's
capable of it's pretty remarkable and
again even more remarkable is that
sometimes organisms can be preserved in
tree sap
in other words like crystallized in
amber and so these are really excellent
examples of fossils but these are not
decaying very much at all and even whole
organisms even down to fur can be
preserved if that organism died in a
really cold environment frozen in ice
like a classic example that would be a
woolly mammoth or a saber-tooth tiger
that died during an ice age and it's
totally preserved or in a real acidic
area like an acid bog where there where
the pH is so low that bacteria is not
are not decomposing very well or a tar
pit these kinds of unusual locations
where you can really get preserved bones
and partment teeth really like yeah
almost like it died did that and you
know that the day after and so
paleontologists talk about dating these
fossils paleontologists have a variety
of ways in which they can date them so
when it when an organism is trapped in a
sediment you can go back and it's sort
of frozen in time and it's obviously
relatively dated in context with other
fossils so fossils above it are
generally younger fossils below it or
generally older and that the younger
ones are sort of superimposed on the
older ones however you can get some
interesting things happening you can
have erosion taking place and so
portions of the rock may be missing but
palings
colleges again just like historians or
crime-scene investigators are quite
persistent in diligent and curious these
are the piece of the qualifications I I
suspect so the strata at one location
can be correlated in time like for
example this area six right here in this
area so different areas and you can sort
of see where the soil type is similar in
an area and this is called indexing
fossils when you when you when you look
at sites that are further away like that
and you're trying to figure out their
distribution and again obviously the
land is subject to erosion and different
physical means but you can sort of date
an area and say that you know this area
a right here which is the top layer is
actually over in relationship to
location one is actually you know the
fourth layer down in this area but you
can sort of index fossils based on their
their location within the strata and you
can compare and look at geological time
scale as you go back now this is when we
talk about time we're talking about a
long long periods of time like millions
of years and so usually you might be
familiar with a with a diagram like this
where we're going back millions of years
100 million 200 million 300 million 400
million years and so this is a vast
amount of time and so paleontologists
have grouped these big swaths of time
into into eras if you've heard that
expression before these periods are
grouped into area as and they're known
as the pre cambian area which is before
the cambian the Paleozoic area the
Mesozoic era and the Cenozoic area and
then you can go back and look at this
and sort of see it will be under these
conditions this is where the first
reptiles appear in the fossil record
this is where we see dinosaurs
diversifying this is the appearance of
the first primate and you can sort of
categorize these things in your study
again they could be rather elaborate I
like this diff
to read this but I understand that I
like the fact that you know these eras
are not necessarily the same timeframe
the pre cambian is a vast amount of time
ok
so hundreds of millions of years versus
these are a little bit smaller and
sometimes these these distinguishment
between era have to do with times of
mastix extinction like for example right
here between the cretaceous area it 65
million years ago was was a mass
extinction v large mass extinction which
eliminated most of the dinosaurs species
on the planet Earth right around the air
so that's kind of interesting and so how
do we date fossils we used radiometric
dating and so that's that usually the
method most used to determine the
absolute age of a fossil and that tracks
radioactivity and isotopes if you're
familiar with this isotopes are our
different species of a element and some
are radioactive which means that their
nucleus is decaying and emitting
radioactive particle and that means that
the isotope declines over time as
especially after they die and so a
radioactive decay is indicated often by
the transfer of one element to another
elements of a parent element to a
daughter element over time and it's
usually a long period of time and so we
usually consider the time it takes for
half of the parent to turn into the
daughter an example of this is carbon-14
paleontologists love the element
carbon-14 because it's a radioactive
isotope of carbon and why that one in
particular well you might know is that
carbon is is the basis of organic
molecules which are found in living
organisms and so real briefly on this is
that you get how does carbon-14 even
come into being well in the atmosphere
cosmic rays excited Neutron which then
caused the neutron to collide with a
nitrogen 14 at
which removes a proton creating
carbon-14
and so carbon-14 is radioactive I'll
dispel like this and so carbon-14 as you
may be familiar with carbon-14 is a
component of carbon dioxide carbon-14
but it's also there's also carbon-12 in
the atmosphere as well and there's a
ratio of these two and so plants or
other I say terrestrial plants but any
photosynthetic autotroph is taking up
carbon dioxide in the atmosphere in this
ratio and then of course animals or
heterotrophs are eating those plants and
so animals contain that same ratio in
all their organic material so all their
other muscle all their bones that any
molecule that has carbon has that same
exact ratio that was in the plant that
was in the atmosphere but this is kind
of obvious when the organism dies it's
no longer breathing and so this ratio
begins to change as the organism becomes
a fossil so carbon-12 is not radioactive
so it does not decay but carbon-14 since
it's radioactive
begins to decay and you could measure
the quantity of carbon-14 remaining in a
fossil and correlate that to the amount
that was present when the organism was
alive and and note the age of the fossil
okay and so carbon-14 decays back to
nitrogen 14 over time hopefully that was
clear so carbon-14 is present in all
living organisms in the same proportion
as in the atmosphere I mentioned that
but when an organism dies the 14 carbon
declines and it come it turns into
nitrogen-14 so how long does it take for
carbon-14 to decline
well again half half the time it takes
for it's like so in other words if you
had two grams and it became one gram of
carbon-14 how long did that take it
takes 5730 years
and so we could determine the amount in
the fossil relative to the one that it
would when it was alive and we can
figure out how old the organism is as a
result of that and so it's a clock
mechanism and basically every half-life
takes five thousand seven hundred and
thirty years and so every 1/2 so 1/2 to
1/4 to an eighth to a 16 fewer and fewer
carbon atoms but again five thousand
seven hundred and thirty-five thousand
seven hundred and thirty-five thousand
seven hundred and thirty until finally
you have the age of the fossil now
carbon-14 s are our fav for dating
fossils especially the relatively young
ones but radioactive isotopes for other
elements do exist and they have larger
and longer half-lives one of them is
uranium 238 it ready for this half-life
of 4.5 billion years even though that's
not present in living organisms it still
found in a significant level in volcanic
rock so this means that if an organism
for example is trapped in a layer of
volcanic rock we could date the the
radioactivity of uranium and deduce when
that organism may have died because if
it's sandwiched in between those two
layers and so I hope this was a an
interesting discussion not too dry on
the fossil record I it's it's again one
of the more important evidences that
organisms have been changing on this
planet Earth and so I hope you enjoyed
it thanks for watching