Video 2.4.2: The magnetic poles flip? You're kidding me, right?

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En provenance du cours de University of Manchester

Our Earth: Its Climate, History, and Processes

91 notes

University of Manchester

Our Earth: Its Climate, History, and Processes

91 notes

Develop a greater appreciation for how the air, water, land, and life formed and have interacted over the last 4.5 billion years.

À partir de la leçon

Formation, evolution, and processes of the solid Earth

Video 2.1.1: How did the Moon form? - Dr. Katherine Joy 14:43

Video 2.1.2: Why is the Moon important to life on earth? - Dr. Katherine Joy 3:04

Video 2.2: What came before plate tectonics?5:43

Video 2.3: How did plate tectonics get discovered?6:12

Video 2.4.1: The Earth's magnetic field7:42

Video 2.4.2: The magnetic poles flip? You're kidding me, right?6:36

Video 2.5: How earthquakes happen14:23

Video 2.6.1: What's inside the Earth?6:05

Video 2.6.2: How do we know about the insides of the Earth?6:09

Video 2.7: How do the plates move?3:38

Video 2.8: How does magma form?11:17

Video 2.9: How were the Himalaya formed?7:56

Video 2.10: Supercontinent Pangaea9:50

Video 2.11: The supercontinent cycle4:05

Rencontrer les enseignants

Prof. David M. Schultz
Professor of Synoptic Meteorology
School of Earth, Atmospheric and Environmental Sciences
Dr Rochelle Taylor
Postdoctoral Research Associate
School of Earth, Atmospheric & Environmental Sciences
Dr Jonathan Fairman
Postdoctoral Research Associate
School of Earth, Atmospheric and Environmental Sciences

Now, perhaps what may be surprising, to you because we live in

this period of relative stasis where the Earth's magnetic field,

has been undergoing very little changes on the scale of human life time, is that.

The earth magnetic field can sometimes reverse.

And what I mean by that, is that the south magnetic pole in the southern hemisphere,

becomes the North magnetic pole in the Southern hemisphere and

thus essentially compasses would, would point the other way.

So where is now we've built compasses to point towards,

the geographic north, after a reversal,

it would be pointing towards the geographic south, the north magnetic pole.

Now, we don't have to worry about this on the scale of a human lifetime.

The last time this happened was 780,000 years

ago when we had last reversed the polarity.

But you can see over geologic time this being the present time and

going back one, two million years that sometimes we're in normal polarity.

Sometimes we're in reverse polarity and this happens.

And it happens, a periodically you can't predict it and it seems to be consistent

with as you'll see a chaotic convective fluid inside the Earth.

And if we go back,

back 5 millions years we can see 24 reversals in the last 5 million years.

Again, now, with this larger perspective, you don't see any periodicity in here.

There's no characteristic time scale of these reversals.

And in fact, with in the last five million years,

we've been actually in a normal polarity for quite a bit of time.

In fact, the longest period.

Since 5 Million years ago.

To illustrate what that might look like, here is a graph

of magnetic field lines, from a simulation by Gary Glassmeyer and

Paul Roberts at in the University of California.

And what they showed.

First in 1995 was

how the Earth's magnetic field could be maintained, through computer simulations.

But then more importantly, how these reversals could happen.

And it was almost serendipitous.

They were trying to model the steadiness, of the Earth's magnetic field and

instead what they modeled.

and, and, and they did capture that but instead they also modeled

one of these reversals by accident and I think that

really illustrates that they were on to something here with their modeling.

So here you can the earths magnetic field lines going in to the earth and

then out of the earth and

of course these would join up out here at some distance from the earth.

And this is the simulation, that and Roberts produced.

Here, you can see the Earth's magnetic field, on the surface of the Earth,

with the inclination into the northern hemisphere, here.

And, out of the southern hemisphere, here.

Further down, in the outer core.

The surface of the Outer Core, you can see much more

much more detail, much more structure in the Earth's magnetic field.

And that's due to the convection going on there.

So if we put this into motion, we can see the convection occurring down here.

We see occasional bubbles of reverse polarity and

move up into the Northern hemisphere and then BOOM there we go.

We've reversed the polarity here of the Earth from where it used to sit

with the blue towards the North and the red towards the South.

And you can see it was quite a chaotic process.

Just like.

The bubbling of liquid, at the base of the core.

Now we can run that through, one more time.

Here we are with blue to the north.

As in normal polarity.

We can see the convection start to get going in the northern hemisphere.

Reds and yellows and oranges moving into the northern hemisphere.

And then boom.

We've reversed, the polarity.

And so, these reversals as I said,

are quite common in the geological record, and I'm going to

talk in the next lecture about how we are able to ascertain that process.

So, to summarize today lecture, the earths magnetic field is a result

of a convecting, conductive fluid within a rotating earth.

And we know that this layer, is the molten iron within the outer core.

We also recognize that the Earth's magnetic field,

has changed over geologic time.

And from the geologic perspective, it can change relatively abruptly.

These reversals may only take 1,000 or 2,000 years to happen.

And the third point, is that the Earth has undergone unpredictable and

aperiodic reversals.

We don't know how to predict them, as you can see from the simulation.

It just is a chaotic bubbling fluid inside the earth,

and as a result there's no real way to predict these things.

And the consequence of that is that they have no periodicity.

There was nothing that we can say,

after say, 500,000 years we can expect a reversal.

So, with that, thanks for attending.

And I'll talk to you in the next lecture.

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