Expanding Earth Hypothesis


According to modern geologic understanding, Earth once had all its land area contained within a single supercontinent called Pangaea that sat one side of the globe surrounded by a single ocean.  Pangaea then broke into many pieces that drifted across the Earth’s surface and into the positions in which we see them now.

Pangaea ~200 million years ago showing today’s continents overlayed.

This is known as the plate tectonic theory.  It states that continents and surface land sit on ‘tectonic plates’ that drift over ocean areas.  As they do so, the plates push the ocean crust in front of them down into the molten area underneath in a process called subduction, and the seafloor expands behind them in a process called seafloor spreading.

There’s also a lesser known yet very interesting idea that holds the Earth was originally somewhat smaller and expanded to what it is now.  The basis for saying this is the observation that if one takes the dry landmasses (continental regions) and rearranges them onto a smaller sphere whose area is equal to the sum-area of those landmasses, the land appears to fit together like pieces of a jigsaw puzzle.

A good summary is given by this video:

A few liberties appear to be taken with morphing/distorting the land shapes but otherwise the fit is quite good.  It is also important that the landmasses are joined with adjacent landmasses that they could have drifted away from.

Below is my own arrangement attempt that doesn’t use morphing.  Click on the image to start the interactive presentation.

The concept of an expanding Earth has been around since the late 19th century but was officially abandoned in favour of plate tectonics in the 1960s.  Since then a few authors have continued to pursue the idea; each proposing differing mechanisms for how the expansion process might have occurred, or leaving left that aspect unanswered.  It will be object of this article to propose a different mechanism than theirs and add further thoughts.


Comparison of Theories

The plate-tectonics/Pangaea theory has its benefits.  It explains the observed current motion of plates and why the continents appear to join together across the Atlantic.  But it also has its problems.  For example, it doesn’t explain why all the land would be situated on one side of the globe, why it would break apart, or how the subducted land can be pushed into a liquid magma of higher density.

The Expanding Earth theory has similar benefits, with the upside that it doesn’t require the land to start on one side of the globe or for subduction to occur.  But has the obvious downside in that it requires the Earth to grow in size – which on the face of it makes no sense.

So it could be said both theories have their share of benefits and problems.  Overall however, the expanding theory appears to have more benefits and might be a better idea – providing, of course, that there was a way for the expansion to occur.


Continental vs. Oceanic crusts

So is it possible that the Earth could have greatly expanded, and if so, how?

An important clue lies in crust thicknesses.  The Earth’s crust varies in thickness but is typically 30-50km over land areas and 5-10km over ocean areas.  There is also a lack of a smooth transition between the two as the thickness changes suddenly at the edge of continental shelves.

Why the distinct difference?  If Earth were originally a ball of molten magma, as is our modern understanding, and its surface cooled, wouldn’t the crust be the same thickness all over?

A response to this might be that ocean crust is thinner because of the water.  But this makes no sense.  Firstly because you can’t have water sitting on hot magma.  If Earth had water at the time, it would be in the form of steam in a very thick and tall atmosphere.  Secondly, water would make the crust underneath cool faster, since it removes heat via convection, making the ocean crusts thicker.

So here is a possible timeline of events that accounts for the different thicknesses:

1.  The Earth started as a lump of molten magma, pulled into a sphere by gravity (where the magma came from is unimportant here).

2.  The surface gradually cooled, losing heat into space, and slowly hardened.  After many millions (or billions) of years, the surface hardened into a thin crust.  Let’s say it was 20km thick at that point.

3.  Something happened that caused the interior of Earth to expand.

4.  The crust cracked into many pieces like fragments of an egg shell.  Those pieces then floated on top of a giant ‘lava lake’.

5.  After a while the expansion process stopped.  The pieces continued floating about, sometimes colliding with other pieces.

6.  The exposed magma began to cool, forming a thin crust.  The land pieces continued to cool and thicken.

7.  The thin crust gradually thickened to around 10km thick and the land pieces thickened to 30km, and mostly stopped drifting.

8.  As temperatures cooled, the steam in the atmosphere condensed and fell, eventually settling into the thinner crust areas and forming the oceans.


“Something happened”?

The above timeline approximately matches the state of Earth as we see it now.  To make it more accurate, ocean crusts would need to be continually forming as the expansion occurred.  This would cause sections of the crusts to be of different ages; becoming younger farther away from continents.

The part we are missing is point 3 where “something happened” to cause the interior of Earth to expand.  What could possibly do that?

The answer to this is complicated and needs to be broken into several parts.  We’ll begin by looking at this density chart:

This shows the density of Earth as a function of radius.  Note that the interior (the core) has the highest density and the exterior (the crust) is the least dense.  There are said to be two reasons for this.  One is that the heavier elements have sunk downward, and the other is that the pressure is higher farther down, leading to greater compression.

The core has a density of 13.1 g/cm3 and is said to be made primarily of iron.  But iron’s density is only 7.8 g/cm3.  So this tells us the iron has been compressed somewhat.  Meanwhile the lower mantle (halfway down) has a density around 5.5 g/cm3 and is said to be mostly silicates.  But the density of silicates (and rock in general) is around 2.5 g/cm3.  So this too has been compressed.

It may seem odd to think of rocks being compressed but it needs to be pointed out that pressures down deep are much higher than what would be normally experienced.


Non-linear compression

The next thing to consider is that compression doesn’t occur in direct proportion to force.  For example, say we have a block of rubber that is 10cm tall.  We place a 1kg mass on it and notice it compresses by 1cm and is now 9cm tall.  We then put another 1kg on it (making the total 2kg) and notice it compresses another 1cm, making the height 8cm tall.

At this point we might conclude that each additional kg will reduce the height by a further cm.  But that couldn’t be true because otherwise 10kg would reduce the height to zero and 11kg would somehow make it negative.

Instead the amount of compression needs to become less and less.  E.g. 3kg might compress by 2.9cm (height=7.1), 5kg might compress by 4.5cm (height=5.5), 7kg by 5.8cm (height=4.2), etc.

So say we have 5kg sitting on top and the block’s height is 5.5cm.  If we add a further 2kg the height will reduce by 1.3cm (making the height 4.2cm).  But if we instead subtract 2kg, the height will increase by 1.6cm (making height 7.1cm).  So adding to an already compressed block yields a small amount of extra compression.  Whereas subtracting the same amount of mass yields a larger amount of expansion.  This is going to be important when looking at Earth.

As additional weight is placed on the rubber, further compression becomes less and less,
making this compression vs. force chart non-linear.


Pressure within a sphere

Next we’ll consider the pressures inside a sphere that results from gravity.  Suppose we have a sphere of uniform density.  It has a mass of one unit (M=1) and a radius of one unit (R=1)  The density works out to ρ=M/volume=3/(4*pi)=0.24, as shown:

What will the internal gravity function look like?  If we set Newton’s gravitational constant G=1 we get:

So gravity starts at zero at the core and goes to 1 at the surface.  What will the internal pressure function be?  Pressure is the sum of gravity times density for all the mass above a location.  It looks like this:

It’s an inverted parabola with a pressure of 0.24 at the core and zero at the surface.

Let’s suppose that this sphere is made of compressible materials and the radius it has is due to gravitational compression. That is to say, its radius would be somewhat larger if there was no gravity.

We are going to redistribute the material inside the sphere.  Suppose this sphere was made up of materials of different atomic weight.  We will bring heavier elements to the central region, and lighter elements to the outer, while keeping the radius the same.  Suppose that after doing so, the central region has double the original density and the outer has half the original density.  Since the total mass remains unchanged, the ‘boundary’ works out at to be at cube-root of 1/3= 0.69.

Comparing this to the previous situation, the gravity function (blue line) looks like this:

The red line is the previous gravity function and the density is shown in brown.  We can see gravity becomes double at the boundary and identical at the surface.  Now how does the pressure function look?

The pressure (blue) at the core has increased slightly compared to the previous (red) situation, while pressure in the outer part decreases largely.  This is most important!

Now what do you think will happen?  Refer back to the rubber block example.  Most likely the inner region will compress by a small amount and the outer part will expand by a larger amount.  This sets off a chain reaction...

1. As the outer region expands, this reduces both gravity and density in the outer region, leading to the outer region expanding further.  

2. As a result of the outer region expanding, pressure above the ‘core’ decreases.  This leads to the core region expanding slightly.

3. As a result of the core expanding, the total radius increases, which decreases gravity farther out.

4. This further decreases pressure in the outer region, allowing it to expand some more.

And so the process repeats itself over and over until the sphere has expanded to a somewhat larger size.


Comparisons to Earth

Does the above sound like Earth?  The inner core of Earth is said to be heavier metals, mostly iron, and the outer regions mostly silicates.  We can be reasonably sure it wasn’t that way originally.  Instead the heavier elements would have been uniformly distributed throughout the magma (assuming Earth was originally a molten magma ball).  Those elements would have sunk slowly inward.  As they did so, the whole pressure dynamic would change and the upper portions would begin expanding, followed by the inner portions, etc.

In short, the sinking of heavier elements to lower depths would cause Earth to expand.  These diagrams give an overview of the process:

Original Earth has heavy and light elements evenly mixed.  Its size is small due to very high pressure.  Outer surface cools to a solid crust.

Heavier elements, like iron, sink toward the centre.  This reduces pressure in the outer regions, causing them to expand, which then allows inner regions to expand.  Surface crusts are cracked and pieces float on newly-exposed magma.

Exposed magma cools yielding a thinner oceanic crust.  Edges remain hot and volcanic as expansion continues.

Earth ends up with a much larger diameter.  Atmospheric water condenses and flows into the oceanic areas.



It is possible that Earth once had a much smaller size due to gravitational compression of the elements that composed it.  As heaver elements sunk inward, this changed the interior pressure dynamics and caused the Earth to decompress/expand to its current size.


Previous Contents Next chapter

Copyright © 2018 Bernard Burchell, all rights reserved.