WEBVTT

00:00:00.367 --> 00:00:01.889
Hi, everybody. Welcome back.

00:00:01.890 --> 00:00:03.449
Today we're covering the content

00:00:03.450 --> 00:00:06.314
that is in Chapter 25
of your textbook,

00:00:06.314 --> 00:00:10.170
and this chapter largely covers
some broad patterns

00:00:10.170 --> 00:00:13.679
with regard to the history of life
on the planet.

00:00:13.679 --> 00:00:16.806
When we were together last time,
we were looking at mechanisms

00:00:16.806 --> 00:00:18.690
that could promote speciation,
right?

00:00:18.690 --> 00:00:21.720
We talked
about allopatric speciation

00:00:21.720 --> 00:00:24.333
and sympatric speciation.

00:00:24.333 --> 00:00:25.629
Today, we're going to look at,

00:00:25.629 --> 00:00:29.010
again, some broad-scale events
that occurred

00:00:29.010 --> 00:00:31.370
over the history of life
on the planet

00:00:31.370 --> 00:00:33.935
that include things
like mass extinctions,

00:00:33.935 --> 00:00:37.895
and the phenomenon
of what we call adaptive radiation

00:00:37.895 --> 00:00:41.973
where we see many,
many species

00:00:41.973 --> 00:00:44.225
show up in-- in the fossil record.

00:00:44.225 --> 00:00:47.138
And yeah, a lot of what we know
with regard to what

00:00:47.138 --> 00:00:50.730
we're going to talk about today
comes from an exploration of

00:00:50.730 --> 00:00:53.369
and interpretation
of that fossil record.

00:00:53.370 --> 00:00:54.881
Starting
with this slide right here:

00:00:54.881 --> 00:00:59.849
this is a amazing photo
of a skeleton of a whale

00:00:59.850 --> 00:01:03.280
that was discovered
in the Sahara Desert.

00:01:03.280 --> 00:01:05.540
So, you might be wondering,
well, how did that happen?

00:01:05.540 --> 00:01:07.760
Researchers were--
were knowing where to look

00:01:07.760 --> 00:01:11.662
when they were--
when they were trying to figure out

00:01:11.662 --> 00:01:16.479
what are the origins
of marine mammals, for example.

00:01:16.479 --> 00:01:20.447
And so, due to conversations
with geologists about,

00:01:20.447 --> 00:01:23.156
you know,
where we might find fossils

00:01:23.156 --> 00:01:27.998
of-- of particular creatures
from a particular time

00:01:27.998 --> 00:01:29.980
in the history of life on Earth,

00:01:29.980 --> 00:01:32.614
and other patterns of--
of events that--

00:01:32.614 --> 00:01:35.974
that led researchers to predict

00:01:35.974 --> 00:01:38.750
that they
might actually find whale bones

00:01:38.750 --> 00:01:40.959
in the--
in the desert of the Sahara.

00:01:40.959 --> 00:01:42.293
And, in fact, they did.

00:01:42.293 --> 00:01:46.110
So, that's just one example
of some of the work

00:01:46.110 --> 00:01:48.749
that paleontologists do.

00:01:48.750 --> 00:01:53.789
Paleontology is the study
of the fossil record.

00:01:53.790 --> 00:01:56.609
So, yeah, let's go ahead
and get started

00:01:56.610 --> 00:01:58.920
building on the work that--
that we have learned

00:01:58.920 --> 00:02:01.328
from paleontologists today.

00:02:04.893 --> 00:02:07.706
So, again, when we
use the word macroevolution

00:02:07.706 --> 00:02:10.761
now we're really talking
about broad patterns of evolution

00:02:10.761 --> 00:02:12.878
that--
that are above the species level.

00:02:12.878 --> 00:02:15.117
So, we're looking at groups
of organisms.

00:02:15.117 --> 00:02:19.532
And when we look in the fossil record,
we do see some trends.

00:02:19.532 --> 00:02:21.352
You know, we see the emergence,
for example,

00:02:21.352 --> 00:02:23.112
of terrestrial vertebrates.

00:02:23.112 --> 00:02:25.615
We see the emergence
of other groups of species as well,

00:02:25.615 --> 00:02:27.257
that I'm going to share
with you today.

00:02:27.257 --> 00:02:30.553
We also see
that mass extinctions occurred.

00:02:30.553 --> 00:02:31.982
And then there's been, you know,

00:02:31.982 --> 00:02:34.436
there's been...

00:02:34.436 --> 00:02:35.836
you know, that has affected

00:02:35.836 --> 00:02:39.360
the evolutionary trajectory
of other species.

00:02:39.360 --> 00:02:41.158
So, we'll talk about that today.

00:02:41.158 --> 00:02:43.704
And then we'll focus
on some key adaptations

00:02:43.704 --> 00:02:45.149
such as flight, for example.

00:02:45.149 --> 00:02:47.428
So, when these new adaptations
arise,

00:02:47.428 --> 00:02:50.650
it allows for what we
call "adaptive radiation".

00:02:50.650 --> 00:02:52.702
I'll talk about that today
as well.

00:02:52.702 --> 00:02:56.972
The possibility
for many new species

00:02:56.972 --> 00:03:01.773
to emerge
over a relatively short period of time,

00:03:01.773 --> 00:03:03.300
and I'm talking geologic time.

00:03:03.300 --> 00:03:06.073
So, you know, short is relative here
in this conversation today.

00:03:06.073 --> 00:03:11.351
But, yeah, when you
have a novel character that arises,

00:03:11.351 --> 00:03:13.200
such as the ability to fly,

00:03:13.200 --> 00:03:15.320
that promotes the possibility

00:03:15.320 --> 00:03:18.023
for the--

00:03:18.023 --> 00:03:21.239
for a species
that has that particular character

00:03:21.239 --> 00:03:24.980
to diverge into many other species

00:03:24.980 --> 00:03:28.875
as they occupy new habitats
that are available to them

00:03:28.875 --> 00:03:31.104
because of that character
that emerged.

00:03:31.104 --> 00:03:35.320
So, yeah, we'll talk about each
of these in detail today.

00:03:37.747 --> 00:03:39.574
All right,
if we're going to have a conversation

00:03:39.574 --> 00:03:41.241
about the history of life
on Earth,

00:03:41.241 --> 00:03:43.881
we might as well start
at the very beginning.

00:03:43.881 --> 00:03:46.718
So--
So, one of our big questions is

00:03:46.718 --> 00:03:48.338
what is the origin of life?

00:03:48.338 --> 00:03:51.311
How did life ever get started
on planet Earth, right?

00:03:51.311 --> 00:03:55.931
And so, I'm going to share
with you some evidence

00:03:55.931 --> 00:03:57.939
that supports the idea

00:03:57.939 --> 00:04:01.552
that the origin of life

00:04:01.552 --> 00:04:04.118
occurred
via these sequential steps

00:04:04.118 --> 00:04:05.557
that you see in my slide here.

00:04:05.557 --> 00:04:07.575
So, it makes the most sense to us,

00:04:07.575 --> 00:04:09.653
and the data support this idea,

00:04:09.653 --> 00:04:11.659
that the first thing
that probably happened

00:04:11.659 --> 00:04:14.718
was number one here,
abiotic synthesis.

00:04:14.718 --> 00:04:17.959
Abiotic meaning non-living, right?

00:04:17.959 --> 00:04:22.454
Abiotic synthesis
of very small organic molecules,

00:04:22.454 --> 00:04:24.694
probably monomers of molecules.

00:04:24.694 --> 00:04:26.643
And then, finally, polymers.

00:04:26.643 --> 00:04:28.414
The joining of those together

00:04:28.414 --> 00:04:31.683
to make those polymers
probably occurred.

00:04:31.683 --> 00:04:36.163
And then, at some point, those--

00:04:36.163 --> 00:04:40.805
those molecules
were probably captured inside

00:04:40.805 --> 00:04:44.588
what we colloquially
call, "protocells," right.

00:04:44.588 --> 00:04:48.616
Proto- meaning first, these--
these precursors to modern cells.

00:04:48.616 --> 00:04:51.149
And then lastly,

00:04:51.149 --> 00:04:54.418
there is evidence
to suggest the origin

00:04:54.418 --> 00:04:57.880
of self-replicating molecules,

00:04:57.880 --> 00:04:59.534
similar to what we see today,
right?

00:04:59.534 --> 00:05:03.506
Self-replicating DNA and RNA.

00:05:03.506 --> 00:05:05.286
All right, let's take a look
at each one of these

00:05:05.286 --> 00:05:07.433
in detail today.

00:05:09.460 --> 00:05:11.691
So, one of the first things
that would have to happen,

00:05:11.691 --> 00:05:13.527
according to
that sequence of events

00:05:13.527 --> 00:05:14.959
that I shared with you previously

00:05:14.959 --> 00:05:17.501
is the abiotic synthesis

00:05:17.501 --> 00:05:20.994
of organic molecules.

00:05:20.994 --> 00:05:25.624
And researchers
in the 1950s were curious

00:05:25.624 --> 00:05:29.052
if that--
if they could get that to occur.

00:05:29.052 --> 00:05:32.700
and, you know, like, the conversations
at the time were

00:05:32.700 --> 00:05:37.169
well, what
did planet Earth's atmosphere

00:05:37.170 --> 00:05:39.321
look like at the time?

00:05:39.321 --> 00:05:40.320
Let me back up a minute.

00:05:40.320 --> 00:05:44.059
We think that the planet formed
about 4.6 billion years ago,

00:05:44.059 --> 00:05:46.619
but for
that first half a billion years,

00:05:46.619 --> 00:05:50.548
so from 4.6 billion years ago
to 4 billion years ago

00:05:50.548 --> 00:05:53.412
the planet
was probably not conducive

00:05:53.412 --> 00:05:56.183
to life ever forming
on the planet.

00:05:56.183 --> 00:05:58.380
There was--
it was constantly being bombarded

00:05:58.380 --> 00:06:03.150
by rocks and debris,
and it was a very hot environment.

00:06:03.150 --> 00:06:05.909
But about 4 point-- billion years ago,

00:06:05.910 --> 00:06:08.249
4 billion years ago,

00:06:08.249 --> 00:06:11.329
the planet cooled off,
the seas formed,

00:06:11.329 --> 00:06:15.247
and the environment was--

00:06:15.247 --> 00:06:18.044
the atmosphere, we don't know
exactly what it looked like,

00:06:18.044 --> 00:06:21.809
but we have some indication

00:06:21.809 --> 00:06:25.841
that there was methane
in the atmosphere,

00:06:25.841 --> 00:06:27.855
and there was ammonia
in the atmosphere,

00:06:27.855 --> 00:06:30.602
and there's hydrogen gas
in the atmosphere.

00:06:30.602 --> 00:06:34.299
And, whether or not it
was a-- a reducing environment

00:06:34.299 --> 00:06:37.200
or an oxidizing environment.

00:06:37.200 --> 00:06:39.505
Not sure.

00:06:39.505 --> 00:06:41.868
That refers to whether--

00:06:41.868 --> 00:06:45.989
you know, today we're living
in an oxidizing atmosphere, right?

00:06:45.989 --> 00:06:50.700
There's oxygen gas in our atmosphere
that will readily oxidize

00:06:50.700 --> 00:06:52.124
other compounds, right--

00:06:52.124 --> 00:06:54.867
steal electrons away from--
from other compounds.

00:06:54.867 --> 00:06:57.460
There was some indication recently

00:06:57.460 --> 00:06:59.929
that the environment was,
in contrast to that,

00:06:59.929 --> 00:07:03.827
a reducing environment full--
full of hydrogen gas,

00:07:03.827 --> 00:07:05.485
like you see here, H2,

00:07:05.485 --> 00:07:07.678
that would donate electrons
to compounds.

00:07:07.678 --> 00:07:10.881
So, regardless of that,

00:07:10.881 --> 00:07:13.605
this experiment right here
shows you an apparatus

00:07:13.605 --> 00:07:16.289
that was set up by a grad student

00:07:16.290 --> 00:07:18.719
from the University of Chicago
in 1953.

00:07:18.720 --> 00:07:20.159
His name was Stanley Miller.

00:07:20.160 --> 00:07:24.479
He and his--
his advisor worked on this project

00:07:24.480 --> 00:07:28.200
where they--
they attempted to simulate

00:07:28.200 --> 00:07:32.635
what they thought was the atmospheric
and oceanic conditions

00:07:32.635 --> 00:07:36.339
on the planet 4 billion years ago,

00:07:36.339 --> 00:07:40.243
to see if they could
get the abiotic synthesis

00:07:40.243 --> 00:07:41.850
of organic molecules.

00:07:41.850 --> 00:07:43.938
So, what you see in this apparatus

00:07:43.938 --> 00:07:45.904
is a container

00:07:45.904 --> 00:07:50.649
that might simulate the ocean.

00:07:50.649 --> 00:07:54.648
And, you know, we know
from volcanic activity in the ocean

00:07:54.648 --> 00:07:57.656
that there are areas where it's--
it's very hot.

00:07:57.656 --> 00:07:59.381
So, they-- they simulated that,

00:07:59.381 --> 00:08:02.696
you know,
providing thermal energy.

00:08:02.696 --> 00:08:04.618
And then, you know,
some of that water

00:08:04.618 --> 00:08:06.745
would, of course, evaporate.

00:08:06.745 --> 00:08:09.020
And this part
of the chamber, here,

00:08:09.020 --> 00:08:10.840
is kind of representing

00:08:10.840 --> 00:08:12.587
what we think
were atmospheric conditions.

00:08:12.587 --> 00:08:16.266
Here's methane, here's ammonia,
here's hydrogen gas.

00:08:16.266 --> 00:08:21.443
He simulated lightning

00:08:21.443 --> 00:08:23.312
with these electrodes here,

00:08:23.312 --> 00:08:25.268
again, providing energy.

00:08:25.268 --> 00:08:27.528
And then,
as that water vapor cooled--

00:08:27.528 --> 00:08:29.197
here's a condenser here.

00:08:29.197 --> 00:08:32.273
input cold--
cold water to cool it off

00:08:32.273 --> 00:08:34.963
to simulate
a cooler atmosphere.

00:08:34.963 --> 00:08:36.661
And then as that water condensed,

00:08:36.661 --> 00:08:39.237
he sampled it from time to time.

00:08:39.237 --> 00:08:42.377
And, honestly,
his graduate advisor

00:08:42.377 --> 00:08:45.336
actually thought
that there was no way that they

00:08:45.336 --> 00:08:49.486
were going to get any kind
of organic monomers anytime soon.

00:08:49.486 --> 00:08:50.984
You know, we thought that,
you know,

00:08:50.984 --> 00:08:54.376
if this happened
on the planet 4 billion years ago,

00:08:54.376 --> 00:08:56.228
how many million years did it take

00:08:56.228 --> 00:09:00.081
to get synthesis
of these organic molecules?

00:09:00.081 --> 00:09:02.541
But, lo and behold,
they actually got results

00:09:02.541 --> 00:09:04.240
in a matter of months.

00:09:04.240 --> 00:09:06.170
Three or four months later,

00:09:06.170 --> 00:09:07.900
they found in their sample,

00:09:07.900 --> 00:09:10.770
when they sampled it
for chemical analysis,

00:09:10.770 --> 00:09:14.160
they found amino acids,
amazingly enough.

00:09:14.160 --> 00:09:17.580
So, this did represent,

00:09:17.580 --> 00:09:21.960
you know, the phenomenon
that abiotic synthesis

00:09:21.960 --> 00:09:25.470
of organic molecules
can indeed occur.

00:09:25.470 --> 00:09:27.030
This was an exciting moment

00:09:27.030 --> 00:09:31.740
because it set the stage for--

00:09:31.740 --> 00:09:33.450
you know,
it set the stage chemically

00:09:33.450 --> 00:09:36.274
for the conditions for life.

00:09:38.430 --> 00:09:40.960
Another burning question,
so to speak,

00:09:40.960 --> 00:09:45.749
that we have is, well,
where did life originate on the planet?

00:09:45.749 --> 00:09:50.284
A lot of interested--
a lot of interest is being paid

00:09:50.284 --> 00:09:54.060
to these alkaline vents
that are in the deep sea.

00:09:54.060 --> 00:09:57.199
Here's a picture of one of these vents
in the slide here.

00:09:57.200 --> 00:10:00.649
These vents release water
with a very high pH;

00:10:00.650 --> 00:10:03.159
9, 10, 11.

00:10:03.160 --> 00:10:05.379
So, they're considered
alkaline vents.

00:10:05.380 --> 00:10:08.799
And also very warm water,
40 to 90 degrees C.

00:10:08.800 --> 00:10:10.629
And the conditions in these vents

00:10:10.630 --> 00:10:13.419
were probably very likely suitable

00:10:13.420 --> 00:10:16.359
for the formation of some
of these organic compounds.

00:10:16.360 --> 00:10:19.659
And, indeed,
researchers have looked at the surface

00:10:19.660 --> 00:10:22.239
of the structures
that formed these vents

00:10:22.240 --> 00:10:25.929
and found organic molecules attached
to those vents.

00:10:25.930 --> 00:10:29.109
So, maybe this
is where life arose.

00:10:29.110 --> 00:10:32.679
Other people are very interested
in looking at meteorites.

00:10:32.680 --> 00:10:36.579
Meteorites may have been
another source of organic molecules.

00:10:36.580 --> 00:10:38.889
For example,
the fragments of a meteorite

00:10:38.890 --> 00:10:40.809
called the Murchison meteorite,

00:10:40.810 --> 00:10:43.719
has been discovered
to contain more than 80 amino acids

00:10:43.720 --> 00:10:45.339
and other key organic molecules,

00:10:45.340 --> 00:10:49.239
including lipids, some sugars,
also some nitrogenous bases.

00:10:49.240 --> 00:10:53.379
So, maybe these are the--
maybe we can--

00:10:53.380 --> 00:10:55.689
maybe we can consider that that is

00:10:55.690 --> 00:10:58.329
where we got
these first organic molecules

00:10:58.330 --> 00:11:03.320
is from the meteorites
that have bombarded the planet.