Learn about the science behind the current exploration of the solar system in this free class. Use principles from physics, chemistry, biology, and geology to understand the latest from Mars, comprehend the outer solar system, ponder planets outside our solar system, and search for habitability in our neighborhood and beyond. This course is generally taught at an advanced level assuming a prior knowledge of undergraduate math and physics, but the majority of the concepts and lectures can be understood without these prerequisites. The quizzes and final exam are designed to make you think critically about the material you have learned rather than to simply make you memorize facts. The class is expected to be challenging but rewarding.
Lecture 4.07: Mars -- Microbial hitchhikers
Loading...
Из курса от партнера Caltech
The Science of the Solar System
310 оценки
Из урока
Unit 4: Life in the solar system (week 1)
Познакомьтесь с преподавателями
Mike BrownProfessor
Planetary Astronomy
In this lecture, I'm going to spin you a story, that is so plausible
that it's easy to feel like it, it almost has to be true.
We'll see what the story is and, we can decide
at the end if we think it really is true.
A couple of really interesting things that have happened in the last decade with
regard to life on Mars, life, on
Earth in extreme environments, and, interplanetary conditions.
One, is that as we discussed way back in unit one, there's
good evidence that Mars started out at least four times, maybe they
were intermittent times, maybe it was an extended period of times, but
where it was, warmer, and wetter in some places maybe predominantly subsurface.
But maybe, there was certainly places, not
just maybe, but there's certainly places on the
surface, where there were things that looked like,
habitable environments, not inhabited environments, but habitable environments.
Another thing that we've learned in the last couple of decades that if you go pick
up meteorites in Antarctica, occasionally you'll get these
very special ones that come from the moon.
And we get ones that come from Vesta.
And, we even get ones that come from Mars.
Materials are transferring back and forth between Mars
and the Earth, Earth and Mars, all the time.
How does that happen?
Well, imagine giant impact comes in and smashes Mars.
Ejecta goes up into the sky, and some of it actually
goes up, and escapes Mars orbit and rattles around the inner
solar system for awhile, eventually finds itself on an Earth crossing
path, hits the Earth's atmosphere, lands in Antarctica, we pick it up.
You probably remember, almost 15 years ago now when there was this huge announcement
that a Martian meteorite had been found
with, evidence for microbial life inside of it.
And, in case you haven't gotten the picture, in the intervening 15 years.
Pretty much, nobody believed that that was
actually evidence for, Martian life inside that rock.
But, it sparked the interest in studying those Martian
rocks, just to learn what we could about them.
And one of the, I think, really interesting
things about, that Martian rock that was found, was
that it retained much of the magnetism that
it had, when it left the surface of Mars.
Now, when you take something that has, a
remnant, magnetic field like we know about Mars.
If you take something like that and you heat it up, the magnetic field that that
material have will slowly decay away, as all
of the, magnetic little dipoles inside there, realign randomly.
So the fact that this, this Martian meteorite, still had,
a remnant magnetic field, meant that it never got very hot.
It never got very hot, and it was ejected into space in an impact.
That's a little bit surprising.
I, I would have guessed, many people would
have guessed that, yes, you can eject stuff
into, into space, but it's only going to be
molten and solidifying as it gets into space.
But no, unmelted chunks, in fact, substantially unheated chunks,
of the surface, of the planet get ejected into space.
And when that happens, they can eventually land on a different planet.
That's one more thing we've learned in the last
couple decades, or maybe we knew this all along.
Which is, life is persistent.
Microbial life is persistent.
Anyone who's ever tried to disinfect their kitchen,
and keep it clean, knows that this is true.
You can, spray as much bleach as you want all
over it, but eventually the little buggers will come back.
Last couple lectures, we talked about, life in all sorts of environments.
And, one of the environments that we've
tested, microbes, and is the environment in space.
We have left, microbes exposed in space for years in
conditions that are, the rad, there should be radiation damage.
They, of course, have no nutrients, no oxygen.
Brought them back down, and they were easily revived.
Not all of them.
But if there are, a particular class of radiation resistant bacteria that,
that can survive in space for as long as we've left them there.
We now have enough pieces to put together, the entire puzzle.
What if, early on in the history of the Earth, Earth were hit
by a large, meteor and chunks of the Earth flew off into space.
On those chunks of Earth perhaps, would have been microbes.
Not just perhaps.
If you picked up a chunk of the Earth,
anywhere around here right now, you would definitely have microbes.
Those microbes, some of them, could survive the rigors of space.
And they would land places.
Where would they land?
Well, maybe they'd land on Venus.
What happens?
They're fried to death.
It's too hot.
Where would they land?
Well, maybe they would land in the sun.
That's not so good either, but
occasionally, they would inevitably land on, Mars.
And remember, this is early on.
They would land on Mars when it was warm, and it was wet.
And what would they do?
Well, I have to tell you, if you took a rock, with microbes on
it, and you put it in a warm and wet environment on the Earth.
You'd get a lot of microbes.
It's hard to imagine that landing on Mars in this environment would not
lead to, a flourishing of a microbial community in the spot where it landed.
It's equally difficult to imagine that, once it gets
established, that it is, it is impossible to eradicate.
Life is hard to get rid of.
It finds these niches, it stays in these niches.
And you can't get rid of it.
If this process ever happened, if microbes transferred from Earth to Mars, it
would be very easy to imagine, that they would still be there today somewhere.
Deep under ground, hot springs, extreme environments, not on the surface.
The surface, even though, we now know it's not
necessarily, sterile, the surface is still a harsh, environment.
So, if I were a microbe today I would be, somewhere underground.
Did this really happen?
Well, yes.
I can tell you some of the parts of the story, definitely happened.
Rocks that were blasted off the Earth, landed on Mars.
Rocks that got blasted off the Earth, probably had microbes on them.
Rocks that got blasted off the Earth but landed
on Mars probably still had living microbes on them.
It's really hard to imagine, a solar scenario in which that doesn't happen.
This leads me, and has led me, you can find me in different places around being
interviewed giving my opinion on this, to say that there must, be life on Mars.
It is harder to imagine that there's not life on
Mars, that there, than that there is life on Mars.
Now, this doesn't mean that life formed on Mars.
I'm just saying that, life has been contaminated, that
Earth has contaminated Mars with life, over billions of years.
And that it's very hard to escape that conclusion.
Although, there is an alternative way of looking at it.
The alternative way of looking at it is that, with, with the thick atmosphere of
the Earth, it's actually a little bit hard to eject the rocks off the Earth.
It's not impossible, but it's hard.
It's a little easier the other way around.
What if.
Mars is a more, hospitable place early on in its warmer and wetter period.
Earth might have been a little too cold at that point.
What if, a rock got blasted off from Mars that didn't
have microbes kind of like that, claim in 15 years ago?
What if it did have microbes, what if it landed on the, Earth,
and what if it found, a hospitable place to develop, on the Earth?
What if.
In fact, we go back and we look for microbes on Mars, and we find them.
And, in fact, we're really just returning to the place from which we came.
Okay, it's a crazy idea but, it's actually not that crazy of an idea.
How would you know?
Well, I, I would say that, if you go to Mars and you find microbes.
When you go to Mars, and you do find microbes.
What will they be like?
If they evolved independently on Mars than on Earth, then, we shouldn't
expect them to be any, like those on the Earth at all.
But if they really were blasted off the Earth, or, they blasted off of
Mars and we evolved from, Martian microbes,
when we get there, they will look familiar.
By look familiar, I mean they will have, same sorts of
DNA, RNA that, that we have that our life is based on.
Hard for me to imagine that two places would evolve,
that sort of, complexity, exactly the same way two separate times.
If you do find it, what is it going to tell us about life?
What is it going to tell us about Mars?
Well, interestingly, less than we might have thought at first.
If we find life on Mars, and that life resembles ours enough to be
convinced that it's a contamination event it
doesn't tell us about the evolution of life.
It doesn't tell us how easy it is for life to form on different places.
What it really tells us about [SOUND] is the resilience of life.
It tells us about, how hard it is
to eradicate life once it gets started somewhere.
And how easy it is to spread, not just throughout our own planet.
But perhaps, throughout the solar system.
Is it a crazy idea?
Yeah, it's a totally crazy idea.
It's hard to, dispute most of the legs of the argument, though.
It's hard to dispute that, somewhere on Mars, one of
these microbes, or the descendants of one of these microbes that
transported across space, billions of years ago is, is still there,
growing deep underground waiting for us to go track it down.
Ознакомьтесь с нашим каталогом
Присоединяйтесь бесплатно и получайте персонализированные рекомендации, обновления и предложения.
Coursera делает лучшее в мире образование доступным каждому, предлагая онлайн-курсы от ведущих университетов и организаций.
© Coursera Inc., 2019 Все права защищены.
