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Hi, everybody. Welcome back.
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Today we're covering the content
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that is in Chapter 25
of your textbook,
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and this chapter largely covers
some broad patterns
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with regard to the history of life
on the planet.
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When we were together
last time,
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we were looking at mechanisms
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that could promote speciation,
right?
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We talked
about allopatric speciation
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and sympatric speciation.
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You know,
today we're going to look at, again,
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some broad-scale events
that occurred
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over the history of life
on the planet
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that include things
like mass extinction
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and the phenomenon
that we call adaptive radiation
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where we see many,
many species show up in--
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in the fossil record.
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And yeah, a lot of what we know,
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with regard to what
we're going to talk about today,
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comes from an exploration of
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and interpretation
of that fossil record,
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Starting
with this slide right here:
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this is a amazing photo
of a skeleton of a whale
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that was discovered
in the Sahara Desert.
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So, you might be wondering,
well, how did that happen?
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Researchers were--
were knowing where to look
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when they were--
when they were trying to figure out
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what are the origins
of marine mammals, for example.
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And so, due to conversations
with geologists about,
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you know,
where we might find fossils
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of-- of particular creatures
from a particular time
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in the history of life on Earth,
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and other patterns of--
of events that--
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that led researchers to predict
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that they
might actually find whale bones
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in the--
in the desert of the Sahara.
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And, in fact, they did.
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So, that's just one example
of some of the work
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that paleontologists do.
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Paleontology is the study
of the fossil record.
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So, yeah, let's go ahead
and get started
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building on the work that--
that we have learned
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from paleontologists today.
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So, again, when we
use the word macroevolution
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now we're really talking
about broad patterns of evolution
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that--
that are above the species level.
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So, we're looking at groups
of organisms.
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And when we look in the fossil record,
we do see some trends.
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You know, we see the emergence,
for example,
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of terrestrial vertebrates.
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We see the emergence
of other groups of species as well,
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that I'm going to share
with you today.
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We also see
that mass extinctions occurred.
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And then there's been, you know,
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there's been-- that has affected
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the evolutionary trajectory
of other species.
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So, we'll talk about that today.
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And then we'll focus
on some key adaptations
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such as flight, for example.
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So, when these new adaptations
arise,
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it allows for what we
call "adaptive radiation".
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I'll talk about that today
as well.
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The possibility
for many new species
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to emerge
over a relatively short period of time,
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and I'm talking geologic time.
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So, you know, short is relative here
in this conversation today.
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But, yeah, when you
have a novel character that arises,
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with the ability to fly,
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that promotes the possibility
for the--
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for a species
that has that particular character
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to diverge into many other species
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that include things
like mass extinctions,
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and the phenomenon
of what we call adaptive radiation.
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that the first thing that probably happened was number 1 here,
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Abiotic meaning non-living, right?
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Abiotic synthesis of very small organic molecules,
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probably monomers of molecules.
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Proto- meaning first, these-- these precursors to modern cells.
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All right, let's take a look at each one of these in detail today.
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according to that sequence of events
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that I shared with you previously
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is the abiotic synthesis of organic molecules.
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And researchers in the 1950s were curious
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well, what did planet Earth's atmosphere
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look like at the time? Let me back up a minute.
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We think that the planet formed about 4.6 billion years ago,
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There was-- it was constantly being bombarded
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by rocks and debris, and it was a very hot environment.
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But about 4 point-- billion years ago,
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4 billion years ago,
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So, regardless of that,
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this experiment right here shows you an apparatus
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that was set up by a grad student
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from the University of Chicago in 1953.
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His name was Stanley Miller.
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He and his-- his advisor worked on this project
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where they-- they attempted to simulate
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what they thought was the atmospheric and oceanic conditions
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up on the planet 4 billion years ago, to see if they could
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get the abiotic synthesis of organic molecules.
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as they occupy new habitats that are available to them
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because of that character that emerged.
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So, yeah, we'll talk about each of these in detail today.
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So, what you see in this apparatus
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is a container that might simulate the ocean.
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All right, if we're gonna have a conversation
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about the history of life on Earth,
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we might as well start at the very beginning.
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So-- So, one of our big questions is
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what is the origin of life?
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How did life ever get started on planet Earth, right?
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And so, I'm going to share with you some evidence
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that supports the idea that the origin of life
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occurred via these sequential steps that you see in my slide here.
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So, it makes the most sense to us,
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and the data support this idea,
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abiotic synthesis.
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And then, finally, polymers.
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The joining of those together
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to make those polymers probably occurred.
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And then, at some point, those--
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those molecules were probably captured inside
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what we colloquially call, "protocells," right?
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And then lastly,
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of self-replicating molecules,
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similar to what we see today, right,
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self-replicating DNA and RNA.
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if that-- if they could get that to occur.
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And, you know, the conversations at the time were,
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but for that first half a billion years,
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so from 4.6 billion years ago to 4 billion years ago
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the planet was probably not conducive
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to life ever forming on the planet.
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the planet cooled off, the seas formed,
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and the environment was--
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you know, the atmosphere, we don't know exactly
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what it looked like,
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but we have some indication
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that there was methane in the atmosphere,
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and there was ammonia in the atmosphere,
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and there was hydrogen gas in the atmosphere.
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And, whether or not it was a a reducing environment
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or an oxidizing environment.
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Not sure.
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That refers to whether--
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you know, today we're living in an oxidizing atmosphere, right?
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There's oxygen gas in our atmosphere that will readily oxidize
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other compounds, right--
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steal electrons away from-- from other compounds.
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There was some indication recently
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that the environment was, in contrast to that,
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a reducing environment full-- full of hydrogen gas,
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like you see here, h2,
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that would donate electrons to compounds.
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And, you know, we know from volcanic activity in the ocean
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in a matter of months.
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that there are areas where it's-- it's very hot.
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Three or four months later,
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So, they-- they simulated that,
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they found in their sample, when they sampled it for chemical analysis,
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you know, providing thermal energy.
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And then, you know, some of that water
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would, of course, evaporate.
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And this part of the chamber, here,
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they found amino acids, amazingly enough.
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is kind of representing what we think were atmospheric conditions.
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So, this did represent,
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Here's methane, here's ammonia, and here's hydrogen gas.
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you know, the phenomenon that abiotic synthesis
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He simulated lightning
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with these electrodes here.
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Again, providing energy.
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of organic molecules can indeed occur.
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And then, as that water vapor cooled--
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here's a condenser here.
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Input cold-- cold water to cool it off
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This was an exciting moment
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to simulate a cooler atmosphere.
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because it set the stage for--
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And then as that water condensed,
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he sampled it from time to time.
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And, honestly, his graduate advisor
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you know, set the stage chemically
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actually thought that there was no way
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for the conditions for life.
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that they were going to get any kind of
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Another burning question, so to speak,
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organic monomers anytime soon.
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You know, we thought that, you know,
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if this happened on the planet 4 million years ago,
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how many million years did it take
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that we have is, well, where did life originate on the planet?
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to get synthesis of these organic molecules?
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But, lo and behold, they actually got results
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A lot of interested-- a lot of interest is being paid
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to these alkaline vents that are in the deep sea.
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Here's a picture of one of these vents in the slide here.
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These vents release water with a very high pH;
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nine, ten, eleven.
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So, they're considered alkaline vents.
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And also very warm water, 40 to 90 degrees C.
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And the conditions in these vents
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were probably very likely suitable
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for the formation of some of these organic compounds.
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And, indeed, researchers have looked at the surface
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of the structures that formed these vents
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and found organic molecules attached to those vents.
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So, maybe this is where life arose.
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Other people are very interested in looking at meteorites.
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Meteorites may have been another source of organic molecules.
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For example, the fragments of a meteorite
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called the Murchison meteorite,
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has been discovered to contain more than 80 amino acids
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and other key organic molecules,
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including lipids, some sugars, also some nitrogenous bases.
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So, maybe these are the-- maybe we can--
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maybe we can consider that that is
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where we got these first organic molecules
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is from the meteorites that are bombarding the planet.