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The Rise of Oxygen: Evolution of Earth's Atmosphere

Video transcript
The video is 7 minutes and 5 seconds long.
Produced by the American Museum of Natural History, March 2004.

Video begins here.

Visual: Early Earth in space.

Speaker: Grant Young, Department of Earth Sciences, University of Western Ontario

When most people think about the planet, they think of it as it is. But when you study geology, you realize that the early Earth was not at all like it is at the present time. 

Visual: Cars travel down a highway, scientists in the car examine road map. Geologists remove equipment from trunk of car.

What gets geologists up in the morning, is the possibility of determining how the earth got to be as it is now. 

Visual: Clouds roll by in the sky.

The appearance of oxygen in the atmosphere is extremely pivotal in terms of how the planet developed, in particular in relation to life.

Visual: Waves roll on to the beach at sunset.

Once oxygen built up to the point that there was an ozone layer, then life could come out of the sea and come onto land because it was protected by the shield from ultraviolet rays from the sun, which are deadly, which can destroy the body of the organism. Oxygen is one of the things that renders our planet pretty unique in the solar system, and possibly in the universe.

Visual: Green leaves frame a patch of open sky. A geologist hammers at a rock, and another examines it closely.

Speaker: Alan J. Kaufman, Department of Geology, University of Maryland

Visual: Alan J. Kaufman sits in his office. Geologists walk up mountain face and hammer and break up rocks.

I’ve often wished that I had a time machine to go back and collect an ancient bit of atmosphere. But we can’t. All we can do is collect rocks that were formed under that atmosphere. So we go into ancient mountain ranges and we collect rocks, and we tease them apart to try to understand processes that tell us something about that ancient atmosphere.

Visual: A geologist takes notes. Another counts ridges in a rock face.

Visual: A river valley

Speaker: Grant Young

The Huronian Super Group is a thick accumulation of mainly sedimentary rocks. At its thickest point, it is about six to seven miles. It’s located at the south edge of the Canadian shield. By radiometric dating we know it’s between 2.47 billion years and about 2.2 billion years.

Visual: Grant Young sits on top of mountain. Other geologists walk up mountain face. Close ups of rock formations.

The Huronian Group is particularly exciting and interesting because, by chance, these rocks were laid down at a period when the atmosphere underwent a transition from containing, we think, no free oxygen, to containing at least some free oxygen.

Visual: Car races past on road. Alan Kaufman examines rocks with magnifying glass.

In order to investigate the atmosphere, we look at minerals in the rocks that react to the presence of oxygen.

Visual: Alan Kaufman in office

Speaker: Alan Kaufman

While we were in the field, we looked at various levels of the Huronian stratigraphy.

Visual: Alan Kaufman describes rocks to Grant Young

What you got here is, uh, sandier layers and muddier layers here. The mud is almost purple in color indicating that, a high iron content. But even the sands are also oxidized, they have this pinkish or reddish color due to hematite.

Visual: Grant Young explaining to Alan Kaufman. Another researcher looks on.

Speaker: Grant Young

So we think it’s very shallow marine, very shallow amount of water above the sediment when it was laid down, therefore a very close contact with the atmosphere. And the atmosphere at this time would have contained at least some oxygen. And so we get this red coloration.

Visual: Alan Kaufman photographs rock face.

Speaker: Grant Young

That red color’s a very good clue because it tells us that there was this reaction with oxygen.

Visual: Grant Young sits on top of mountain

It’s a very simple kind of test, but it, but it does give us at least the first order idea as to whether there was free oxygen and whether there wasn’t. 

Visual: Alan Kaufman labels rock sample with marker. Another researcher takes notes.

Speaker: Alan Kaufman

This will be sample KY03-5.

Visual: Alan Kaufman places rock sample in bag.

The rocks that we collected from various levels in the Huronian stratigraphy we’ll bring back to the laboratory.

Visual: University of Maryland Department of Geology signage on department door. A researcher takes the rock sample from a cabinet, and places it in grinding equipment. Another researcher works with chemistry equipment, and a small gas bubble forms in a test tube.

We’ll chip them with hammers. We’ll crush them in grinders and eventually the powders we’ll extract with various chemicals to pull out sulfur, because it’s sulfur that’s telling us something, we believe, about the ancient atmosphere.

Visual: Animation of volcano spewing yellow sulfur dioxide gas.

Most of the sulfur in the atmosphere comes from volcanic explosions, and that sends a gas called sulfur dioxide high into the stratosphere.

Visual: Animation of the sun emitting ultra-violet radiation.

In the presence of UV radiation, sulfur dioxide will interact with ozone to form a certain compound of sulfur that gives us a signature that we can read in the rocks.

Visual: Animation of sulfur-infused rain raining into a body of water.

However, in early Earth because there was no oxygen there was no ozone. And without the ozone there’s no reaction and there’s no signature in the rocks.

Visual: In a laboratory, a scientist attends to geochemistry apparatus.

And it’s those ancient rocks that we’re now bringing back to the laboratory to study that ancient atmosphere.

Visual: The scientist extracts a tiny air bubble from a pipette. Another scientist sits at a small scale and weighs a small amount of rock powder.

Speaker: James Farquar, Department of Geology, University of Maryland

To better understand what the sulfur signature meant, we went out and decided to analyze a variety of samples from Australia, Africa, Greenland, North America, South America and Asia.

Visual: A scientist attends to a large machine. James Farquar in his office.

And the conclusions are that the change from a large signature to a much smaller signature of about two and a half to 2.45 billion years ago is a result of a large change in atmospheric oxygen content, from levels 100,000 times less than present to levels within about 100 times of present levels.

Visual: Scientists gather around computer monitors and apparatus to examine data

Speaker: Alan Kaufman

The most exciting thing to me about this research is that it quantifies amounts of oxygen in the atmosphere.

Visual: Alan Kaufman in laboratory, examining data on computer monitor.

Before we just had this qualitative sense of, well, it was low here, it must have risen here. But the sulfur signatures that we’re seeing allow us to actually get at numbers.

Visual: Grant Young hammering at rock face. Another researcher carries rock samples, Alan Kaufman hammers at rocks.

The study of the ancient atmosphere does tell us something about the evolution of the life on this planet.

Visual: Alan Kaufman examines rock sample with a magnifying glass. Researchers walk along road under a looming rock face.

We have an intense desire to know where we came from, and that knowledge drives us to understand the earliest biology, the earliest atmosphere, what is the origin of life.

Visual: The researchers continue hammering the rock face, taking notes, and walking up the mountain.

And those are the driving forces that send us into the field to study these truly ancient rocks.

 

Video ends here.

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