2.7. Throwing Rocks at Earth: The Martian Meteorite

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From the course by University of Illinois at Urbana-Champaign

Emergence of Life

60 ratings

University of Illinois at Urbana-Champaign

Emergence of Life

60 ratings

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

From the lesson

Week 2 - The Tree of Life and Early Earth Environments

The advent of life on Earth came about as a result of a remarkable confluence of physical, chemical, and biological processes, all of which were intrinsically linked to rapidly changing early Earth environments. Within this context, cutting-edge approaches in molecular phylogeny by Professor Carl Woese revealed new understandings of the emergence of life and the possible distribution of life within the cosmos. All this and more will be explored in this week's lessons!

2.1. The Scientific Inquiry of Carl Woese8:00

2.2. The Place of Carl Woese in Evolutionary Biology8:24

2.3. Revolution of the Tree of Life7:41

2.4. Evolution of the Tree of Life6:42

2.5. How Did Life Emerge?5:25

2.6. The Genetic Code and Evolutionary Theory7:23

2.7. Throwing Rocks at Earth: The Martian Meteorite10:46

2.8. Microbial Mats and Stromatolites: Laying Down On the Job6:49

2.9. Oxygenation of the Atmosphere5:15

2.10. Snowball Earth; It Did Freeze Over!8:31

Meet the Instructors

Bruce W. Fouke, Ph.D.
Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology

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Mars has given us a lot of good things over the history of time.

Mars has given us, first of all, the ability to be fascinated about

a red planet that we actually can see with our naked eyes on some nights.

It's a place that has driven all kinds of science fiction fantasy and

invasion of the planet.

It was very important, of course, for

ancient cultures in its position within mythology and other aspects of culture.

Mars is a critical component of the human experience, but

something about Mars that we don't think about is how fundamental it's been for

driving forward our ability to understand a new

version of evolutionary biology in the context of a changing Earth.

And that fundamental capability of Mars

to change the way we think was driven by the following.

Every year, a huge amount of rock material, and

I'm measuring this in terms of tons.

So tons and tons of rock material on a yearly basis has been dislodged from Mars,

because of meteor impacts blasted into the solar system,

thrown into the pathway in which the Earth is spinning around the sun.

And every time the Earth goes through a dust-and-rock field

that was generated by debris being blasted off of Mars from meteor impacts,

every time the Earth goes through these clouds of dust and rock, that dust and

rock is collected into the atmosphere and falls to the Earth.

Now we know some of this from the space shuttle heat shields.

The heat shields have been analyzing, every time the space shuttle goes in and

out, it would collect rock and dust material.

And by analyzing the chemical composition

of the rock material that is collected from the heat shields,

Mars has a very distinct chemical signature from that of Earth.

So we have a fingerprint.

If we have a rock that came from Mars,

we can tell that distinctly from a rock that came from Earth.

Now what's really exciting about this

is that not only are the space shuttles great collectors of martian rock and dust.

But on a natural process, rock and dust hits the Earth,

it settles through the atmosphere, it hits the planet's surface.

And the rock and dust that hits the surface on the ice fields,

places like the Antarctic where we have 1.8 kilometers of ice that's just sitting

there on the poles, that ice field becomes the perfect trap for

collecting dust and rock that falls in from space and hits the planet.

Now at any one time, that dust and rock will hit the surface of the ice and

as more snow falls and more ice is formed, then that dust and

rock gets collected and trapped within the ice.

Now ice sheets like the Antarctic are really dynamic places, and by that I

mean that, in some places, they're forming and in some places they're melting.

And on a yearly basis, parts of the ice sheet are known to actually melt or

what we call ablate, go from one phase that's actually a solid ice phase

directly into a gas phase without becoming a fluid or water.

So parts of the ice sheet are changing and going from solid ice, into water vapor.

And in those places, the ice sheet deflates,

it actually decreases in mass, and anything that's trapped within the ice,

becomes sitting on the top of the ice as the ice slowly fades away and

becomes more compressed and dense underneath of it.

So you have the ice sheet then disappearing and its rock and

ash and particle load that is collected over the millennia,

is now sitting free on the surface because of that deflation of the ice.

Well, NASA's known this for a long time.

So, every year NASA scientists go up and they take snowmobiles.

And they collect all kinds of meteors that have hit the Earth.

Meteors are actively flying through space.

And meteorite is one of these meteors that has hit the planet and stopped moving.

So they go around the ice sheets and

collect meteorites off the surface of the Antarctic.

Those meteorites are put into massive collections that

are held at the Smithsonian or at NASA or at other places.

And they're held for future analysis by scientists because every year enough

are collected to overwhelm the scientific community.

There's a lot of material that needs to be looked at.

Well we got really lucky

because of a confluence of circumstance that came together.

One of those was that NASA had an ongoing research program in terms of looking at

meteorites that have hit the earth and then looking for

fossil evidence of what that life is.

Another one is that some of the right meteorites were actually collected, and so

there's a famous one that ended up being the rock sample,

the meteorite that changed the face of science and our ability to understand

evolutionary biology, and that's called the famous Martian meteorite.

The Martian meteorite was given a name.

It's ALH84001,

ALH84001.

If you google that number, you will be amazed at what you find.

That was the number given to that particular meteorite that

was collected in the year 1984, hence the number 84.

And it was collected from a part of the antarctic

ice sheet called the Alan Hills, ALH.

And the Alan Hills region of the ice sheet at that time in 1984,

there was a beautiful, potato-sized rock that was laying there, a meteorite.

And it was collected, given that catalog number, and then put into a collection.

Well a few years later,

a NASA scientist, especially out at NASA Ames Research Center out in California,

they started looking for fossil evidence of microbes within rock.

And it's not easy to do.

Microbes, their average diameter is one micron, these are small,

small creatures, and they have many

aspects of them that are hard to distinguish from non biological entities.

So telling the difference between a biological fossil and

a non biological fossil that's on the scale of one micron, is a major challenge.

So NASA scientists were looking carefully at these meteorites that were collected.

And the ALH 84001 turned out to be a piece of orthopyroxene.

Orthopyroxene is a form of igneous rock.

Igneous rocks you know about, more commonly, are things like granite.

People like to put them on their countertops.

Well, orthopyroxene is another form of igneous rock.

It's crystals that cool and grow together that come out of a molten mass of rock.

And this particular meteorite,

it was formed originally as a igneous rock on the planet Mars.

And then, while it was still on Mars, it formed,

became a solid rock, and it was fractured.

We don't know exactly the process that fractured it, but

some kind of strong geological process would've had

to have fractured the rock while it was still a component of the crust of Mars.

Now after the rock was fractured, waters started moving through the rock.

And as waters move through rock like that, often times they'll precipitate minerals.

So you can have elements that are dissolved in water and

if you flow the water over something,

change some of the physical chemical conditions, you can actually have those

elements go from being ions in the water to something that's solid.

Now you do this in reverse all the time.

If you want to put sugar into your coffee, you'll put sugar in and

then you'll stir it.

And it goes from a solid sugar clump into disappearing,

which means all the ions that make up the sugar go into the water.

So as these waters on Mars flowed through these fractures into the piece of

orthopyroxene, they precipitated a very important mineral,

the mineral calcite, calcium carbonate, CaCO3.

And Calcium Carbonate is really important to us because calcium carbonate is often

associated, not always, but is often associated with biological activity.

If something's living there and they do some kind of a process to keep themselves

alive, then one of the things that happens as a result is the water will

allow the ions to go from being dissolved to being a solid mineral.

So these solid rock minerals actually grow out of the water as the water flowed

through these cracks and they were trapped in the calcium carbonate, and

filled up this fracture in this igneous rock from Mars.

Now we have good and very excellent analogs for

this comparative environments on Earth where we see this happening all the time.

A very famous one is mammoth hot springs in Yellowstone National Park where

the waters come up to the surface of the Earth after being heated by

a super volcano.

They are full of ions that once the water is cool and

allows some of the gas to escape from those waters,

they precipitate calcium carbonate at incredible rates, very, very, very fast.

So we know from Earth environments that this can happen.

Well, all this process took place on Mars, but

then one thing happened a very long time period after that rock was formed.

Is that a meteor hit Mars, created a crater and

then blasted rock material into space.

Then that chunk of orthopyroxene, where the fracture filled with calcium carbonate

with potential microbial fossils in it, it traveled through the solar system.

It left the orbit of mars, went into orbit around the sun, and

as the earth came around, it entered the Earth's atmosphere and

then plunged to Earth in the Antarctic.

Then the funding agencies especially in the United States, but

also in other countries began making opportunities for

scientists to look carefully at what is a fossil

that is microbial in origin versus what is a fossil that is not microbial in origin.

And therefore, the famous martian meteorite opened the door for scientific

discovery to lay the boiler plate then for us to understand the genesis of life,

not only on planet Earth but also potentially on Mars.

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