The Fossil Record

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historical documents of our of our time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


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


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


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


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


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