How Likely Is A Slippage Of The Earth's Crust?

[Coley]

How likely is a slippage of the Earth's crust? Is it thought to have happened in past ages? I understand that an increasing shift in the Van Allen belts has occurred over the last century and a half. Since the crust floats on the core, how far is the estimated shift necessary to cause such an event?

[CraigD]

Hi Coley – welcome to hypography! :)

 

How likely is a slippage of the Earth's crust? Is it thought to have happened in past ages?

The crust slips and shifts almost constantly. Most of the time, it’s unnoticed, but large and sudden enough shifts, we experience as earthquakes, about 270 of them a day. About 5 times that many are too faint for people to feel, but are detected by seismometers.

 

Though the crust is constantly, slowly, changing, not only slipping, but new crust forming and old being absorbed (via subduction), from what we can tell via science, the rate and violence of this hasn’t changed much in the last 3,800,000,000,000 years. From about 4,600,000,000,000 to 3,800,000,000,000 years ago, the Earth appears to have had some really rough times, especially around 4,500,000,000,000 years ago, when a collision of Earth and a moon-sized co-planet, Theia, is hypothesized to have formed the Moon.

 

Since the crust floats on the core ...

The Earth's crust doesn't float on the core, but on the layer between it and the core, the mantle. Between the mantle and the inner, solid core is an outer, liquid core, which is very important to the discussion that follows.

 

I understand that an increasing shift in the Van Allen belts has occurred over the last century and a half.

This is true, but appears to have nothing to do with shifts in the Earth’s crust.

 

The particle counts of the inner and outer Van Allen belts change in responses to various natural – mostly changes in the Sun’s output – and occasionally artificial – such as high-altitude nuclear weapon tests – causes. What keeps them in place – prevents them from just dissipating into space – is the Earth’s magnetic field.

 

The Earth’s magnetic field is believed to be caused, not by its crust, inner core, or mantle, but by convection in its liquid outer core

 

We know from the geological record that Earth’s magnetic field changes extremely over short (by geological standards) time periods, reversing polarity roughly every 100,000 to 1,000,000 years, and that for about 1,000 to 10,000 years around the time of the reversal, the Earth’s magnetic field is very weak. When the magnetic field is very weak, the Van Allen belts should nearly disappear. Between reversals, the magnetic field shifts around and varies in strength a lot – at present, the magnetic poles are moving about 50 km each year, and the strength of the field decreasing by about 1% every 10 years.

 

This trend may reverse, or continue, and a field reversal occur – at present, we don’t know enough about the outer core, and aren’t able to measure it in enough detail, to predict its future and the future of the magnetic field.

 

Reassuringly, along with the geomagnetic record, we also have the fossil record, which indicates that nothing too dramatic – no big die-offs, etc. – happens to plants and animals during pole reversals, so when the next one happens, any humans around on Earth will likely be OK.

 

Here are some wikipedia articles backing up the above: dynamo theory, earthquake, geomagnetic reversal, giant impact hypothesis, Hadean, structure of the Earth

[Coley]

Hey Mr. D,

 

I want to look up pole reversals and a few other things. I still have some questions, but I don't know enough to know how to ask them. I am scientist, but a biologist with a specialty in colonial photosynthetics. If you think of anything else let me know. I'll get back to you. Appreciate it. Thanks for the Howdy...that was nice.