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Origins of Life

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Brief History of Earth 0:05
    • About 4.5 Billion Years Old
    • Started Off as a Fiery Ball of Hot Volcanic Activity
  • Atmospheric Gas of Early Earth 2:20
    • Gases Expelled Out of Volcanic Vents
    • Building Blocks to Organic Compounds
  • Miller-Urey Experiment (1953) 5:41
    • Stanley Miller and Harold Urey
    • Amino Acids Were Found in the Sterile Water Beneath
  • Protobionts 8:07
    • Ancestors of Cells as We Know Them
    • Lipid Bubbles with Organic Compounds Inside
  • Origin of DNA 12:07
    • First Cells
    • RNA Originally Coded for Protein
    • DNA Allows for Retention and a Checking for Errors
  • Oxygen Surge 14:57
    • Photosynthesis Changes Oxygen Gas in Atmosphere
    • Cells Absorb Solar Energy with Pigment and Could Make Sugars and Release Oxygen
  • Endosymbiotic Theory 18:22
    • First Eukaryote was Born
    • First Proposed by Lynn Margulis
  • Multicellular Origins 23:08
    • Cells That Kept Close Quarters and Stayed Attached Had Safety in Numbers
    • Hypothesis
  • Cambrian Explosion 26:22
    • Explosion of Species
    • Theory and Snowball Earth
  • Timeline of Major Events 32:00

Transcription: Origins of Life

Hi, welcome back to, this is the lesson on origins of life.0000

First, we are going to talk about where earth came from because that is where life as we know exists.0006

Brief history of earth, it is about 4.5 billion years old, I put a little approximation summation symbol there0012

because depending on what source you look in, what textbook, some may say 4.45 or 4.48, around that time.0018

About 4.5 billion years ago is the age of the earth.0027

Form from a coalescing matter into a spherical form.0032

I would not get into a lot of detail here, you can take an astronomy course, astrophysics course,0035

that can explain more details about that.0041

After the Big Bang, after the universe originated, you have a lot of matter coming together in different ways,0044

forming the galaxies, forming stars, as we know them.0052

For the earth, you just had this, what is natural for matter to do, coming together in a very spherical form.0056

At first, it was not the earth as we know it, it was not this blue planet with lush green life.0064

No, it started off as a fiery ball of hot pot volcanic activity.0070

Its early stages, as far as we know, just all kinds of magma coming up through the surface,0076

just very hot and full of volcanic activity.0084

Volcanic activity still exists today, I do not want you to think that it completely ended.0088

There are always volcanic activity happening in various places on earth.0093

We just do not hear about it all the time.0097

But if you look into it, there is still quite a lot of volcanic activity.0099

Back then, in earth’s early years, eventually you had enough cooling,0103

enough calming down of that frequency volcanic activity to have a crust.0110

There was not a crust at first but eventually the lava is cool enough to create it.0116

Once you have land, once you have something that is a little bit more stable and cooler,0120

you can then have some more steps leading towards life.0125

Like I said magma still exists underneath, plenty of it.0129

Volcanic activity is continuing worldwide.0133

Here is an image of that volcanic activity.0136

Speaking of volcanic activity, all of those eruptions, all of that spewing of gas from the earth's surface created an atmosphere.0142

Because of the earth’s gravitational pull, that contributed to a lot of gases hanging around.0152

We have this atmospheric layer, actually several layers, around the earth’s surface.0158

Compared to the earth itself, in terms of the earth’s diameter, the atmosphere is actually quite thin.0165

I have heard it is described as if you had a globe and you put some lacquer finish on the outside,0170

that is analogous to how thin the atmosphere is to the actual diameter of the earth itself.0176

But, the question is, what kind of gases do we usually have on earth’s surface?0182

The key to knowing about earth’s early gases, what came out of volcanic vents?0189

What came out from those volcanic eruptions?0194

If today, you were to go to where a volcano is actively erupting and you are using tools to measure what levels of0198

what gases do we have coming out from this volcanic activity, here is some of them, 0205

not all of them but you would find carbon dioxide, water vapor, nitrogen gas, hydrogen sulfide, methane, plenty of other ones.0211

I did not list them all here, there are actually a few other ones that I list on the next slide, 0222

when we talk about Stanley Miller and Harold Urey.0229

This little group of gases here does not support life.0233

The first atmosphere on earth, actually for a while, 0239

it would have not been able to support mundane animals that alone, most life forms on earth.0243

It would be toxic levels, none of the gases that support life.0248

Speaking of not supporting life, this is not actually earth’s breakdown of gases.0252

This is what we know as Mars atmosphere.0258

Check it out, almost all the gas is carbon dioxide.0263

You might think that plants can get by.0267

This is too much CO₂ level for a plant.0270

Argon, nitrogen, oxygen, carbon monoxide, carbon dioxide, would be the other ones0274

that you would find on earth's early atmosphere that is by itself, toxic.0278

Gases from this time contain the elements, the building blocks for organic compounds.0286

If you look at what you got here, we got carbon, oxygen, hydrogen, nitrogen, and sulfur.0292

Get some phosphorus in there, few other things, you have got all the building blocks you need to make cells, eventually.0301

Think about it, CH and O, that is in every organic compound or molecule.0308

Nitrogen, you would find in nucleic acids and proteins.0313

Sulfur, you definitely find in a particular amino acid, as well in proteins.0319

Those building blocks are there, just not in the right form, not in the right combinations yet.0324

How do you get from inorganic gases to organic compounds?0329

How do you get from gases that are not the building blocks of life to the building blocks of life?0335

The answer to that question from previous slide is Stanley Miller and Harold Urey’s experiment.0343

The Miller-Urey experiment from 1953, these two scientists demonstrated 0348

that you can get organic compounds from inorganic starting materials.0352

Here is how they demonstrated it.0357

They had a setup with gases, these are among them, from early earth, like what we talked about in the previous slide.0359

In a glass container, this little spherical container here, with electrodes attached to it so you could zap them.0366

And that is suppose to replicate lightning.0372

If you imagine having these gases in Earth’ early atmosphere,0375

getting enough water vapor up in the atmosphere, you can get lightning storms.0379

The theory was that, maybe over time, lightning zapping these gases could have made a lot of these elements0384

get mixed up in different combinations because of the electricity.0393

They wanted to demonstrate that it is possible.0397

They have a kind of replication of ocean here with water, heat source.0399

You are going to have that heat source from hydrothermal vents, from vents that heat the water.0405

There is lot of theories about how early cells may have come into being in these like hot pools in the ocean.0414

You have heat here, you get some water vapor coming up in here.0423

You create basically, kind of a little mini atmosphere there with lightning.0427

You got a condenser here, cool water wrapped around this particular tube.0432

That can encourage these gases to end up coming down into the liquid.0437

The interesting thing is after they zap these gases repeatedly, they found what was sterile water here,0443

just water with no organic compounds in it.0449

They found amino acids among other organic compounds.0453

They proved it is possible that if you zap these gases enough,0458

you can get them rearranging in interesting combinations like an amino acid or a simple sugar perhaps.0462

The amazing thing is they proved it, the year it happened in 1953 overshadowed by another very famous discovery,0468

the double helix structure of the DNA from Watson and Crick.0478

But I think that the Miller-Urey demonstration is equally as important.0482

Once you have got all these different organic compounds just floating around the ocean,0489

they demonstrated that they could end up there naturally.0494

How do you get to cells?0498

Protobionts, this is a nickname for the earliest cells, almost like the prototype for what became the cells as we know them today.0500

You can start with lipid bubbles.0511

If lipids could end up in the ocean and they could have because of the Harold Urey demonstration.0513

Imagine having some lipid bubble like this, because think about when you put lipids, like oils,0521

vegetable oil and olive oil in water, like in the ocean.0531

They do not mix very well because of the non polar-polar difference.0534

Lipids are non polar, water is a polar molecule.0538

They do not mix very well.0541

Lipids could have formed these little bubbles.0543

Guess what, the plasma membrane is a very lipidy structure, it is phospholipid bilayer.0545

That is part of what keeps else separate from the external environments.0550

If you have lipid bubbles floating around, maybe they could have encapsulated some molecules.0554

You can imagine having little amino acids in there, I’m exaggerating the sizes of these.0562

It has got amino acids.0572

How did it get from amino acids to proteins?0574

One of the explanations is they have done studies with clay.0577

Clay is a natural substance you can find in various parts of the soil, various parts on earth.0584

Clay is one of those substances that, if you put amino acids in water that has a clay layer,0591

something about the clay actually encourages amino acids to stick together and stay together.0597

It has a catalyst for making those initial peptide bonds between amino acids which is great.0602

If you put amino acids together, without that clay, they might stick together0610

but they will end up breaking apart, not too long thereafter.0615

Clay could have possibly encouraged the formation of some of these first proteins.0619

RNA would be the next step.0624

RNA ends up being a molecule that we know about today that code for an amino acid sequence.0626

If you look at the RNA lesson in this course, you can see that various kinds of RNA help make proteins.0633

They help get those amino acids together in a particular sequence.0640

RNA could have ended up in the cells, something ended up being compatible about sequences of bases matching certain amino acids.0645

The exact mechanism of that is not completely understood.0667

There are various theories that explain how do you get from having a little simple protein sequences in cells0670

to having RNA that can code for them and regenerate them.0676

I do no have all the answers to that.0681

One of the things that need to be connected from here to the next step is, how do you get DNA?0683

Without DNA, you cannot pass on that code effectively to the next generation.0690

You do not retain that code for making these different compounds.0695

No DNA organelles at first, therefore, no evolution.0701

These first cells would have existed, faded away, existed, faded away, almost like a trial and error.0705

It could have happened many times until you get to the point where you can retain that code and pass it on.0712

And then, evolution truly begins.0717

Once you have DNA, once you have proteins that can copy that DNA, that is the key.0720

The origin of DNA, how do we get there?0729

The very first cells that function similarly to what we see today, 0732

would have had RNA that actually does code for amino acid sequences, but no DNA yet.0736

To get the DNA, you definitely need that other side, you need that double stranded molecule.0743

Change the sugar a little bit, one of the bases becomes different, if you remember the differences between DNA and RNA.0749

Once RNA can give rise to that double stranded molecule, that can be replicated, it can be passed on to daughter cells.0755

RNA originally coded for protein, as far as we know.0763

There was no retention of that code.0766

By retention, I mean being able to preserve it, and a double stranded molecule is perfect for that.0769

Think about this, here is that point.0775

DNA allows for retention and a checking for errors because of attached compliments.0778

Think about this, if this green and red molecule is your double stranded DNA molecule.0782

The red would be your template strand, this goes back to transcription.0787

Here is that template strand and here are your bases.0797

The yellow, I will do this in black because it is hard to read yellow.0800

Here is your RNA, realize that all of these bases are green but that does not matter for this picture.0805

Think about this, if you can have DNA as a double stranded molecule, making RNA at a moments notice.0814

Just cranking RNA when needed and getting data out to other part of the cells to code for protein.0821

The brilliance of having DNA is, if that part or of this part, any of these nucleotides get damaged, there is a mutation that changes.0826

The brilliance of it is, if this changes, the other side has the appropriate compliment.0838

Since A and T go together and C and G go together as compliments, you know what belongs there.0844

When this gets changed, just look at the other side.0850

If both sides get changed, that would be a terrible mutation if both parts end up being wrong.0853

With sexually reproducing organisms, you can look at the other homologous chromosome and see that 0860

what should go there to have normal or wild type DNA that codes for the appropriate to molecules.0866

That is a brilliant thing about DNA and retention of the code.0873

With RNA, if you do not have any DNA in the cell and just RNA that gets damaged,0877

how does a cell know what should belong there to code for the appropriate protein.0882

They would not know.0887

DNA is a great way to retain that code, duplicating both side of the DNA0888

and passing that on is a way that evolution gets kicked started.0892

Oxygen surge, imagine for hundreds of millions of years you have got singled cell beings, 0899

some of them would be considered chemoautotrophs.0907

Autotroph meaning that they are self energizing, meaning making their own food but they are not using light.0914

Photoautotroph would be describing plants, moss, algae, various plant like organisms that actually do photosynthesis.0925

Chemoautotrophs is not using light, it is using gases and heat coming from hydrothermal vents to make sugars and lipids, and any other food source.0936

Chemoautotrophs probably existed early on, that relates to archaebacteria, this is way before eukaryotes, by the way.0949

We do not have mitochondria or chloroplasts, or nuclei yet.0958

We would have ribosomes, those are not membrane bound organelles.0963

Those are needed to synthesize proteins.0966

Chemoautotrophs probably would have got the process started.0970

Next up, you can have photoautrophy and eventually heterotrophy comes into play.0973

Once you have supplies of food being made, you can have other cells that end up consuming them from outside of themselves.0980

Heterotrophs like us that eat but not like us because we were talking single celled, ancestors of modern day bacteria here.0988

Anyways, in the first couple of billion years of worlds existence, there was little to no oxygen gas in the atmosphere.0996

Completely toxic, in terms of any modern day animal trying to be successful there.1003

How you get to the point where there is enough oxygen gas?1009

Now, our atmosphere, oxygen gas levels is over 20% of the gas volume, in terms of how much oxygen is there.1012

The dawn of photosynthesis really changed it.1022

Thanks to the ancestors of plants, once cells could absorb solar energy with pigment,1026

such as chlorophyll, they could make sugars and release O₂ as waste.1033

Because oxygen gas is a waste product of photosynthesis.1038

Lots of photosynthesis, for millions of years, would have had the surge of oxygen in the atmosphere.1042

And then, that would pave the way for aerobic respiration.1049

Without a significant amount of oxygen gas in the atmosphere, 1054

aerobic respiration would have been evolved as a worthwhile process that actually has benefits.1057

For aerobic respiration to take place, you need oxygen.1064

If the oxygen is not there, this would not have come into play as, this is the way to go,1067

this is how you get a lot of energy by using that oxygen.1071

Having oxygen gas in the atmosphere paves the way for what enables us to survive and the average animal to survive.1075

This image here is chlorophyll B, chlorophyll B is one of the few different types of chlorophyll.1083

Magnesium is a very important element in the formation of chlorophyll.1091

Thanks to this molecule, you can actually absorb solar energy.1095

How do you get to the point where you actually have eukaryotic beings, cells with membrane bound organelles,1104

a nucleus, mitochondria, chloroplasts, ER, golgi, etc, how do you get that?1111

For hundreds of millions of years, there are only prokaryotes,1117

this means before a nucleus, before the kernel meaning that nut looking structure of the nucleus.1121

Prokaryotes for so long before you finally get eukaryotes.1130

How do you get there?1136

There is the endosymbiotic theory, this is also known as endosymbiosis.1138

A symbiosis or a symbiotic relationship in biology is where two organisms have some kind of dependency on each other.1142

A lot of times we talk about that in a positive light, like mutualism or commensalism, has a positive factors to that.1151

Sometimes it is parasitism too, that is another different kind of symbiosis that has a negative for one side of it.1162

Symbiosis is this kind of relationship between two different species.1167

Endosymbiosis is telling us that something is inside.1172

It is a good description because here is what we think happened.1178

At some point, a smaller prokaryote was engulfed by a larger prokaryote.1181

Almost as if it is going to eat it via endocytosis.1187

Endocytosis was brought in the cell transport lesson.1192

Endocytosis is how a cell would swallow up or engulf a very large molecule, like a macromolecule or a smaller cell.1199

In this case, this cell that was engulfed, the smaller prokaryote was not consumed.1209

It stayed inside and allow to benefit for the small one and the large one to happen.1215

The first eukaryote was born by this.1222

Here is a little illustration of what could have happen.1225

The only problem I have with this is, we do not know for certain that 1227

this first eukaryote actually had a nucleus yet, it is possible they did.1231

I have heard different theories of where the nucleus could have come from.1238

You could have had an invagination or kind of pinching in of part of the plasma membrane 1242

that ended up wrapped around DNA and the nuclide region, to get that first nucleus.1247

There are other theories that actually suggest that, you could have had a cell either devoid of DNA1252

or DNA that did not end up in the nucleus but engulfing a cell inside of it,1261

much smaller cell that actually took the place of the genetic material.1267

There are a lot of different theories about how it could have happened.1271

There is your nucleus with your nucleoli.1275

Anyways, they think that an aerobic bacterium, an ancestor of modern day bacteria 1277

that actually did aerobic respiration, like a mitochondrion.1284

The mitochondrion helps to break down sugars with the help of oxygen to make a lot of ATP.1289

This bacterium was doing that on its own.1294

If it ends up inside of it, you can get the ancestor of mitochondria.1297

On the other hand, a cyanobacterium, meaning a bacterium that does photosynthesis, 1302

this would be an ancestor of blue green algae, could have come in.1309

If you are wondering, what about these little inner membranes,1313

these could have occurred also by a pinching in of pieces of the bacterial plasma membrane 1317

and having these little units that increase the surface area,1323

where you are going to have more reactions pertaining to aerobic respiration and photosynthesis.1326

When this comes in, it also was not consumed.1335

This cell, what you end up getting here, this is after many generations of evolution, of course.1338

What you end up getting here is the ancestor to our plant life because you got mitochondria and1344

you have got chloroplasts, what eventually to become chloroplasts.1350

If we are talking about the ancestor of animal cells, you have the same scenario but 1353

without the chloroplasts, you would have mitochondria.1358

Who suggested this?1363

This theory was first proposed in the 1970’s by Lynn Margulis.1365

Great theory and it is definitely a sound theory about how this could have happen.1370

Interesting fact about Lynn Margulis, she was married to Carl Sagan.1376

If you do not know about the great Carl Sagan, I highly suggest looking him up.1381

You got eukaryotic cells in the ocean, floating around, doing their thing, doing photosynthesis, 1390

eating molecules from outside of themselves.1396

How do you get to bunches of cells interacting together as one organism?1400

How do you get to multicellularity?1405

For multicellular origin, you could potentially have cells that kept close quarters and stayed attached,1408

safety in numbers and they can begin taking on various roles.1419

Here is one hypothesis, if you have a unicellular flagellated protists,1424

you will hear more about protists in the taxonomy lesson and the lesson on kingdom protista.1429

If you had a single celled eukaryote with a little flagella swimming around in the ocean, 1436

you could have a bunch like it that eventually come together as an aggregate, a group together.1442

All of them moving their little tails can move around this little group.1450

It is a safety in numbers kind of thing.1453

They are bigger and better, in the community of flagellated protists swimming around.1457

You could have the unspecialized flagellated cells form a hollow sphere.1463

The hollow sphere, if you are wondering what is the significance of that?1470

That eventually ends up helping to form layers between levels of tissue.1473

When you study about how an early embryological fold happens in animals, 1479

that pertains to having various layers inside of the body that is going to develop.1486

When we get into that later on in this course, you can find that out when we discuss about how animal body forms develop.1491

Specialized reproductive cells can form because that is how you end up getting the ability for this group of cells1503

to make more groups of cells that are together as one unit, as one organism.1510

This little area that is kind of colored in sort of a reddish purple.1515

That is the area where these cells start to take on the ability to do meiosis.1520

Because if they all have a certain chromosome number, 1527

all it takes is this doing some kind of division that results in that haploid number, that half the number that the other cells have.1529

All it takes is two ½, something would be analogous to sperm and egg, to combine to make a new whole.1538

A new diploid that then would divide to make another group of these.1545

Another step is, if they fold in to make tissues, this is the very kind of basic start to 1549

how you get layers of tissue whether it is diploblastic or a triploblastic.1558

You can learn about those later on, when we get to the basics of embryology pertaining to animal body forms.1565

To this could be a really reasonable hypothesis for how you get the original multicellular cells, multicellular organisms rather.1571

The Cambrian explosion, in terms of progression of complex life, 1584

we have talked about how you get from inorganic compounds or inorganic molecules to organic compounds, 1589

how you get to the first cells, how you get to eukaryotic cells, how you get to multicellular life?1596

In terms of the progression of complex life, they were just a few major steps up until 0.5 billion years ago.1603

Once you get was to 500,000,000 years ago, it is the same as 0.5 billion years, then you get a lot more major steps.1612

It is almost exponential how it got from the beginning of earth up until now,1619

with the amazing diversity of 100,000,000 species or more on earth.1624

During the Cambrian period, an explosion of species occurred.1630

The Cambrian explosion is not an actual boom like dynamite, it is not boom goes the dynamite here.1634

Its boom goes the species explosion.1640

Based on the fossil record, especially places like the Burgess shale, I will give you some examples down at the bottom here about that.1643

There are many other fossil sites but this is one of the more famous ones, where we discovered around 5,000,000 years ago, 1656

there all these fossilized early animals, the ancestors of all vertebrates, the ancestors of so much life today, 1663

that had some very interesting body forms pertaining to life up until this point.1674

And other body forms that just kind of disappeared, stuff that existed for a little bit, was not successful, did not have descendants.1680

You get some really weird things going on but the Cambrian explosion was such a huge contributor to biodiversity today.1689

How do you get from not much success with biodiversity to all of a sudden lot of species?1698

The theory is that earth was an extremely harsh place to live, just prior to this Cambrian period.1705

They even called it snowball earth.1710

There is enough geologic evidence to suggest that, if you look at earth back then, here is earth on its axis, spinning around.1713

If you look at earth way back then, supposedly, instead of it just having ice up here and a lot of ice down here, 1724

you had a lot more ice, a heck of a lot more ice like a really intense cool period for millions upon millions of years, that is snowball earth.1734

There was hardly any area for life, as we know it, to successfully exist.1748

It probably did mostly at the equator region where it was a little bit more tolerable, in terms of temperature.1754

Once this thaws out, once the earth then gradually transitions into a warmer period, it starts to thaw and the snowball melts.1762

And then it is like a sigh of relief for all these organisms that survived, like this is actually much more tolerable.1776

It paved the way for having a spreading out of organisms, greater rate of speciation.1785

Here is a couple of interesting examples from the Burgess shale.1794

This particular animal, freaky worm looking thing, this is one of the many body plans 1800

that has been discovered from that Cambrian period, in terms of fossil evidence.1806

This here, very famous fossilized form called a trilobite.1811

Trilobites came to being during this Cambrian period.1819

You can see it looks like it has the segmentation and basic body plan of something like a centipede or millipede.1824

This is one of the earliest arthropods.1833

Arthropods are the phylum of animals that includes all insects, arachnids, crustaceans, and the like.1843

Very early example of this thing that would have been patrolling around the ocean,1853

probably a filter feeder, definitely a sexual reproducing organism.1859

The ancestor of arthropods as we know it.1864

Another weird example is an organism whose genus name has been given is this, hallucigenia.1868

It has been called hallucigenia because the body plan is so weird, the fossilized remnants of this is so weird, 1875

it is almost like the viewer is hallucinating like how could this possibly be.1884

The image is something like this.1888

It has these legs coming in out of the bottom.1899

Here is the head end, the tail end, this little spike looking things.1901

As far as we know, this does not have any modern day descendants but it existed about ½ billion years ago.1905

It has fossilized remnants, look it up, if you like.1915

A timeline of major events, specially in the last ½ billion years.1921

Keep in mind that, if we were look at a timeline of earth, I’m just going to briefly show you this.1928

If here is the beginning, this is time zero - about 4½ billion years ago - and here is now.1933

If we were to mark the billions of years, here is a 4½, here is going to back about a billion years, 2 billion years,1944

3 billion years, 4 billion years, 4½, all of these you are going to see here is right in this little chunk, amazingly.1952

That is why I said that the progression of life to the complex that we know it today is very exponential, in the sense of the timing of it.1962

You would have had the first cells existing somewhere way back here.1971

You would have the first eukaryotic cells around this time.1977

It took a heck of a lot longer to finally get to the point where you have multicellularity being successful,1981

vertebrae ancestors as we know them today.1991

Here is about 500,000,000 years ago and that is where we are going to start out.1993

The first important kind of event I want to point out is about 443,000,000 years ago,1998

you have the first vertebrates, as far as we know.2013

Please keep in mind that this is all approximate.2017

Even if you look up these periods of time form the Cambrian, all the way up to the quaternary period,2021

these are just approximates.2028

These periods are contained within eras, you got these major eras.2032

We are now in the Paleozoic era.2036

Eventually, we will get to the Mesozoic where you see more dinosaurs and finally to the Cenozoic, modern era.2040

Eons have the era, eons are very long amounts of time.2046

Periods smaller, contained within them.2052

About almost 500,000,000 years ago, the first vertebrates.2056

About 416,000,000 years ago, this would be land plants.2060

Think about this, before this point in time, we have no evidence of plants on land.2067

For so long we have photosynthesis only happening in the ocean.2074

Today, it still happens mostly in the ocean.2077

Bony fishes is 359,000,000 years ago, I forgot the year in front of that one.2084

I will write it here, 359 you get bony fishes.2091

Before then, you had crabs, cartilaginous fishes, soft bone fishes, 2098

or organisms that were swimming around but did not have a skeleton.2104

299,000,000 years ago, amphibians, these are individuals that actually have that dual life2112

meaning born in the water as fishes are, but the ability to come on land for periods of time,2125

as modern day frogs can do and salamanders.2134

You got other amphibians that can be on land for a lot longer.2137

They do not dry out, they are not as dependent on water.2143

About 200,000,000 years ago, you have your first dinosaurs and mammals.2147

Now prior to then, you definitely have reptiles.2163

You definitely have reptiles coming into existence, that is how you get dinosaurs, that is how you get mammals.2166

There actually are transitional fossil forms from reptile to mammal 2174

that show you that there was a gradual transition until you finally get, now they are officially mammals separate from reptiles.2179

Dinosaurs and mammals coexisted, we know that know.2188

Dinosaurs definitely had their heyday prior to mammals.2192

Mammals at that time would have be much smaller.2195

Of course dinosaurs had some pretty big ones.2197

The first birds about 145,000,000 years ago.2201

I forgot to write the year here but I told you that is about 145, first birds came from reptiles as well.2207

In an earlier lesson I showed you an image of archaeopteryx, that was a transitional form between reptiles and modern day birds.2224

About 65,000,000 years ago, I’m going to tell you that based on a new story I read recently, this is probably much earlier.2235

I read recently that there were actually fossils of flower imprints found much older than this, 2244

closer to more like 100,000,000 years ago.2254

The flower fossil record has been pushed back recently.2260

Based on a textbook that I looked in this morning, the textbook is only two years old, 2263

said that about 65,000,000 years the first flowers existed.2270

We would have had plant life giving rise to other plant life via seeds prior to flowers2273

because you do have plants out there like cone bearing plants that make seeds without flowers.2279

Flowers is definitely a big step because once you have flowers, they are pretty and they got that nectar.2285

You are going to have pollinators taking advantage of that and flowering plants are really the most successful plant,2293

in terms of how widespread they are and how many species there are.2299

That is a big step in plant evolution.2303

About 34,000,000 years ago, I want to get tight coming up here.2306

About 34,000,000 years ago, mammalian orders meaning the different groups of mammals, 2311

you finally see examples of all of them or most of them.2319

Monkeys at about 23, you finally see monkeys.2324

Apes, 5.3 the fun of this is how tight it gets.2338

This just goes to show that the exponential factor I was explaining before.2344

The funny thing about this whole sequence, 2351

this numerical sequence from about 0.5 billion years ago up till now is that, this is not even to scale.2356

Think about this, if this is too much over 5 million years ago, 138 should not be right there, 2364

and 66 should not be right there, certainly 1.6 should not be there.2371

Whoever made this chart is jumping at different lengths of time to try to fit this in and2375

make it kind of an even spacing between the periods.2383

Putting all of this on this particular timeline to scale,2388

it would be almost impossible to show all these events right in that little span of time.2393

We are hugging this little area right next to now, present day.2398

5.3 we finally see apes.2404

I will tell you the last two because they are really hard to fit in.2409

Hominins meaning specifically that group that includes home habilis, homo erectus, homo ergaster, etc.,2414

you finally see them appearing right here prior to the quartenary.2423

And then us, 200,000 years ago, and then modern day looking homo sapiens closer to 50 to 30,000 years ago.2428

It is just amazing the dominoes that led from way back when in the Cambrian explosion, 2440

all the way up to this incredible diversity of life and drastic speciation that has led to life today, as we know it.2448

Thank you for watching