00:00:00
yo what's up in this video we're going
00:00:03
to have a look at early Evolution so
00:00:05
thank you for coming back so let's have
00:00:07
a look at what happened shortly after
00:00:09
abiogenesis which we met in the last
00:00:11
video and let's look at a period when
00:00:14
life was getting a foothold on Earth so
00:00:17
if there's one thing I can tell you
00:00:18
about this time period is that there are
00:00:20
lots and lots of Fairly open questions
00:00:22
that remain much like those questions
00:00:24
that we saw when we were looking at a
00:00:26
biogenesis and the different theories by
00:00:28
which that may have originated so things
00:00:30
that I can tell you for sure are the
00:00:33
life nowaday uses RNA shown on the left
00:00:36
hand side of this image here and DNA on
00:00:40
the right hand side of this image as
00:00:41
informational molecules these are long
00:00:44
molecules and as I said they are
00:00:47
generally informational they store
00:00:48
information for living
00:00:50
things what happened immediately after a
00:00:54
biogenesis is still very poorly known
00:00:57
but what we think may have happened is
00:01:00
that longer and um increasing numbers of
00:01:03
molecules were created through the
00:01:06
evolution of early
00:01:08
life now um we think that uh simpler
00:01:13
molecules than RNA that's shown here may
00:01:15
have been around first for example there
00:01:18
is a thing called TNA this is uh 30's
00:01:22
nucleic acid or PNA peptide nucle
00:01:25
nucleic acid another form of long long
00:01:27
molecule but with a different kind of
00:01:29
backbone may have existed before
00:01:34
rned the evidence for that is is lacking
00:01:37
um we don't have rocks from this time
00:01:39
period or indeed any remnants of uh the
00:01:42
biochemistry of the things that were
00:01:43
alive in this period to test that idea
00:01:45
but it kind of as a first principle
00:01:48
makes sense that we may want to start
00:01:49
off with a simpler molecule than
00:01:53
RNA after that however most people do
00:01:56
agree that there was a period um in
00:01:59
which life was all RNA based it used
00:02:02
this molecule uh shown on the left here
00:02:06
which was we call the RNA world so RNA
00:02:09
is a kind of like an allinone molecule
00:02:12
it's it's generally single stranded has
00:02:14
one backbone as opposed to DNA which has
00:02:17
two and as well as storing information
00:02:21
it can catalyze reactions there are
00:02:23
things called rymes that catalyze
00:02:26
reactions and this means that rnas have
00:02:30
the capacity to carry out a wide range
00:02:33
of important biochemical functions and
00:02:35
they would have been a very good
00:02:37
candidate for the earlier informational
00:02:40
molecules um before the Advent of DNA
00:02:44
during this time um we think as well as
00:02:48
having the evolution of RNA after the
00:02:50
origin of life we would have seen the
00:02:52
origin of cells to house and prot
00:02:55
protect genetic
00:02:57
molecules at some point or also there
00:03:00
must have been a switch towards DNA as
00:03:04
opposed to RNA and that kind of actually
00:03:07
does make a bit again of first principal
00:03:09
sense RNA is relatively unstable
00:03:13
compared to DNA for example uh the M you
00:03:16
know viruses tend to use RNA and there
00:03:19
could even be a hangover of the RNA
00:03:21
world one of the reasons you and I um
00:03:24
get colds many years and indeed why
00:03:27
covid is kind of moving across the world
00:03:29
still going into new forms is because
00:03:31
RNA is relatively unstable so viruses
00:03:34
mutate relatively quickly that can help
00:03:37
you uh survive if you're a virus that
00:03:40
takes advantage I suppose of other um
00:03:44
cells that do your application for you
00:03:46
but if you want a
00:03:47
longstore um repository of your genetic
00:03:50
information maybe that's not so good and
00:03:52
so DNA is actually a better solution to
00:03:55
storing your genetic
00:03:57
information so that must happened at
00:04:01
some point after abiogenesis of
00:04:04
course so by this uh point in kind of
00:04:09
your your reading and your education you
00:04:10
may well have come across this idea that
00:04:12
all life is related and we can place it
00:04:15
onto a evolutionary tree and this is one
00:04:18
example of such an evolutionary tree
00:04:21
otherwise known as a
00:04:23
cladogram so this is a cogram that shows
00:04:26
the relationship between all different
00:04:29
forms of of life just arranged into a
00:04:31
circle to make it a bit more compressed
00:04:33
and make make it so I can fit it onto a
00:04:35
single slide um this shows the
00:04:38
relationships between all major groups
00:04:40
of organisms that are alive on Earth
00:04:42
today if you think about this um kind of
00:04:47
idea of a tree and implication of that
00:04:50
and the theory of evolution and
00:04:52
hierarchical nesting and branching of
00:04:54
forms is that at some point there must
00:04:56
have been a population of organisms from
00:04:59
which everything that is alive today
00:05:01
descends that's marked by the star on
00:05:05
this clayr here and this is a thing that
00:05:08
is called the last Universal common
00:05:10
ancestor which is often abbreviated to
00:05:12
Luca as shown here I'm going to be
00:05:14
saying Luca um for the rest of this
00:05:17
video because it just makes life a lot
00:05:19
easier we can tell by looking at what
00:05:23
all life shares some elements of the bio
00:05:26
biochemistry of Luca so for for example
00:05:30
we can say that it must have had
00:05:32
ribosomes to make protein it probably
00:05:34
had DNA to store its genetic information
00:05:38
and it had chromosome something that
00:05:39
we'll get on to
00:05:41
later other details such as what kind of
00:05:44
organism it might have been and other
00:05:46
elements of its physiology are slightly
00:05:48
harder to get at but actually this is an
00:05:50
area of really active research people
00:05:53
are using the shared genetic Heritage of
00:05:56
all life at the moment to rebuild a kind
00:05:59
of a
00:06:00
an idea of the repertoire of different
00:06:02
genes Luca might have had and then you
00:06:05
are using that to say something about
00:06:07
how it metabolized and so that's a
00:06:09
really interesting and exciting area at
00:06:12
the moment and if you want to explore
00:06:14
this um Tree of Life further you can do
00:06:16
so at this URL here which I will link to
00:06:20
um below this video so you can actually
00:06:23
start explor the inter relationships
00:06:25
between these groups
00:06:32
so if we're thinking about life um in
00:06:36
this tree likee framework and we're
00:06:37
thinking about what happened after this
00:06:40
last Universal common ancestor we can
00:06:43
say that there are three fairly
00:06:45
fundamental splits in the tree of life
00:06:48
the pro cariot that's a word that I put
00:06:51
on the the the bottom here the procar is
00:06:55
a shorthand term for two of those three
00:06:58
um uh spits those two two of those
00:07:01
groups that um represent an early
00:07:04
branching in the tree of life and those
00:07:06
proc carats are members of the groups
00:07:09
the bacteria and the archa these are
00:07:12
organisms that look like what you can
00:07:15
see give or take on this slide
00:07:18
here um 10,000 species of pro cariot
00:07:22
have been described and these are
00:07:25
organisms that split by binary fish and
00:07:27
they just kind of generally pop po a
00:07:30
clone they are normally smaller than 10
00:07:33
microns in size um this is a a kind of a
00:07:37
very simplified diagram showing many of
00:07:41
the um elements of the architecture of
00:07:43
their cells that they share their cells
00:07:46
lack a nucleus or any form of internal
00:07:49
membrane bound structure those are
00:07:52
things that we call organel in organisms
00:07:55
that have them they the um Pro cariot
00:07:59
these ARA and the bacteria um contain in
00:08:02
their cytoplasm in the middle of their
00:08:03
cell uh a single Loop of DNA
00:08:09
and the differences between those two
00:08:12
groups of proar the ARA and the bacteria
00:08:14
um generally revolve around the
00:08:16
chemistry of their cell wall that
00:08:19
surrounds the cell and the methods by
00:08:21
which they synthesize proteins from
00:08:24
their DNA that process that I talked
00:08:26
about a couple of videos back now the AR
00:08:30
include the
00:08:31
methanogenic um archan the those that
00:08:34
metabolize methane in anoxic conditions
00:08:38
and for example the bacteria include
00:08:40
photosynthesizing cyano
00:08:42
bacteria so that's a a very very brief
00:08:46
overview of the pro carots for you so
00:08:51
it's then um very likely that the
00:08:55
earliest traces of life on Earth we will
00:08:58
see in the fossil record probably
00:09:00
represent a pro cariot grade of
00:09:03
organization because the other group of
00:09:05
organisms that includes fungi and
00:09:07
animals for example we think uh results
00:09:10
from uh Evolution based on Pro carots
00:09:13
and of the different procar
00:09:16
groups and there is a fair amount of
00:09:19
debatable evidence for traces of life
00:09:23
from early Earth so a lot of these will
00:09:26
try and use uh geochemistry of rocks to
00:09:28
unravel when life may have appeared for
00:09:31
example that will often include um isot
00:09:34
isotope ratios of carbon in early rocks
00:09:38
that are carbon rich and there are even
00:09:41
papers that kind of talk about potential
00:09:43
fossils all the way back to 4.2 billion
00:09:47
years ago I would say that all of those
00:09:50
need to be very carefully considered and
00:09:53
more um competing um potential pieces of
00:09:59
evidence for early over life keep on
00:10:01
appearing and in all of these there is a
00:10:04
rich ongoing debate about the strengths
00:10:07
and the weaknesses of the different
00:10:09
forms of evidence for early life on
00:10:11
Earth um I don't have time sadly in this
00:10:15
lecture to give you chapter and verse on
00:10:17
all of that so I thought I would finish
00:10:20
this video by introducing um these
00:10:23
3.4 billion year old um fossils from a
00:10:27
place called strell pool in um in
00:10:30
Australia which I think is arguably the
00:10:33
best supported evidence fossil evidence
00:10:36
we have for early life well you can see
00:10:39
examples um photographs of the
00:10:43
structures that are found in
00:10:46
uh uh silicon dioxide Rock from early
00:10:50
Earth at the top here and in this
00:10:54
paper all the papers that I have
00:10:56
reference the bottom here the authors
00:10:58
even to conduct 3D reconstructions to
00:11:01
allow us to understand the morphology of
00:11:03
these structures slightly better and I
00:11:07
believe that these teams of researchers
00:11:10
make a convincing case based on both the
00:11:12
morphology the shape of these structures
00:11:16
and their chemistry to suggest that
00:11:19
these May well be the uh reliable early
00:11:23
traces of a pro cariot type organism and
00:11:27
the arguments from chemistry surround
00:11:30
not only chemistry that may reflect um
00:11:33
their original makeup but help but also
00:11:37
reflect arguments regarding how they may
00:11:40
have been preserved in the environment
00:11:42
in which they were
00:11:44
living so those are if the um these
00:11:48
authors are correct those are indigenous
00:11:51
microfossils preserved within a beach
00:11:54
rock um dripstone fabric so these could
00:11:58
be traced the amongst the earliest
00:12:00
traces of life on Earth that were
00:12:03
actually preserved in situ from a really
00:12:05
ancient Beach and I think that's really
00:12:06
really cool and they're 3.4 billion
00:12:09
years old so that's still quite old and
00:12:12
a really nice example of potential
00:12:15
fossils of early life on
00:12:17
Earth and that brings me to the end of
00:12:20
this video so I will see you very
00:12:22
shortly in the next one take care
