Let’s say the way this planet works is an onion. There are many layers and they interact in ways far more complex than onion rings. Yet we have to start somewhere, and peeling back the layers of this onion can at least help us grasp the huge holes in our understanding.
Let’s start around the middle of the onion at the surface of the earth. A very significant transition takes place here between land and water on one side and air on the other. The water is confounding because it fills in low areas we might be inclined to call land if there were no water there. These low areas get quite deep and are so extensive that 70% of the planet is covered by ocean.
The ocean and the atmosphere have mirror image onion layers beginning with a mixed layer and progressing to stratified layers.
The lower image above is the ocean and the upper the atmosphere.
The Aristotelian elements, air and water have different properties, but at the interface and extending up ten kilometers in the atmosphere and down somewhat less than a kilometer down in the ocean are turbulent mixed layers. These mixed layers both transition, up and down respectively, to stratified layers that make our onion proud. The atmosphere has more layers and is more complex because gravity assures that cold materials go nowhere but down and warm materials go nowhere but up. The ocean below the “clines” is simple and incredibly stable because there is nowhere for it to go. It is constrained at the bottom by another Aristotelian element, earth.
There are generally two sorts of earth, continents and ocean basins.
This graphic by NASA shows the general layers of oceanic crust.
This graphic (credit unavailable) is a good general representation of the onion rings of sediments overlying the different sorts of igneous rocks (ocean and continental and their relative densities) and the mantle layer below. The oceanic crust is to the right and continental crust to the left.
Since we are downward bound from the middle of the onion, lets head for the center of the earth.
This graphic (credit Geopangea Research Group) is a good representation of the earth’s internal onion rings. Each layer is known from a change in velocity of seismic waves from earthquakes.
Problems with our understanding of the onion begin at the core. It has long been posited that convection within the outer core creates the earth’s magnetic field. A nice, easy answer, but it happens that Iron melts above its magnetic Curie point. Above the Curie point a material loses its magnetic properties.
Let’s just say we have no idea how the earth’s magnetic field is generated.
The seismic waves from earthquakes show us amazing things. Above the core/mantle boundary there are two very interesting extrusions.
To me they are doughboys. Credit Ritsema. One can think of them as Atlas holding up the earth. The important thing is they flatten out at the 660 km discontinuity like thunderheads hitting the stratosphere.
We have long been told that mantle convection causes the continents to move.
Childish conceptions like this. Credit unavailable.
The very same seismic waves that illuminate the doughboys show us this simply isn’t true.
The mantle is substantially stratified. Nothing anywhere near mid-ocean convection driving ocean floor spreading is in evidence.
These sections from Kutowski et al (2008) show that the ocean ridge system is in fact a shallow feature. It is readily apparent down to 100km but vanishes as a linear feature before the 660 discontinuity and is unrecognizable in the Perovskite at 1000 km in the lower mantle. At the core/mantle boundary at 2800 km all that remains is the doughboys.
If the doughboys are feeding the ridge system at all they are doing it through tiny venturi in the Perovskite and then spreading out as massive sills. Other offset venturi through the intervening layers and the Mohorovicic (MOHO) discontinuity would then need to feed the sinuous dead end rivers of the ocean ridge system.
Doesn’t really work for me but the raw edge of human understanding does not bear waxing pedantic. Another very serious problem is that the MOHO just below the crust marks the beginning of a low velocity ductile zone generally referred to as the “asthenosphere”. It is on this layer that crustal “plates” are supposed to be moving. Trouble is, seismic waves appear to show that continents have roots far deeper than this.
Credit NatureGeo. Continents appear to have roots that extend to 400 km near the base of the Olivine layer and the ductile material that allows their movement may be more a result of local pressure from movement forces than from a continuous ductile layer.
Let’s just say we have no idea why the continents are moving.
We are working our way backwards from the core of the onion and listing the problems with our understanding. We have reached the surface where we live and where we started. Take a deep breath of the atmosphere.
The atmospheric mixed layer, called the troposphere, is thought to have varied in average temperature within a range of six degrees for all of geological time. We happen to live in one of half a dozen glacial periods known in geological time so it is comparatively chilly out. Furthermore, the last three glacial periods including our own have been characterized by oscillations between glacial and interglacial episodes. We live towards the end of an interglacial.
We have no idea what causes glacial/interglacial fibrillations nor what causes the macro scale glacial periods to come along every few hundred million years.
This is what the descent into our current ice age, the Pleistocene, looked like.
Let’s just say we have no idea why the mixed layers of the lower atmosphere and ocean warm and cool.
The next layer of the atmosphere is the stratosphere. It’s a long way back to the first graphic so it is reiterated here.
Temperature declines steadily through the mixed layer or troposphere for a bit over 10 km and suddenly flatlines up to about 20 km where it starts warming again and this warming accelerates through the ozone layer in the mid stratosphere. The warming continues well above the ozone to the top of the stratosphere at about 50 km where cooling resumes throughout the mesosphere to about 80 km where it flatlines and then warms in the thermosphere.
One weird onion. Strange how the speed of sound follows temperature rather than density. We ain’t done yet. There is at least another 100 km “sphere of influence” above the thermosphere.
This is a NASA image of the Van Allen ring currents, more a donut than onion rings.
In this graphic from the Chinese Academy of Sciences we reach the outer skin of our onion. Beyond the onion we get into the rest of the universe, 95% of which seems comprised of dark energy and dark matter of which we have no understanding.
So what is the state of the onion? It is just a silly metaphor to attempt to reduce head spinning complexity to something we can get our heads around, yet even at this dumbed down level our understanding utterly fails.
1. We have no idea how or even if the planet’s core produces the earth’s magnetic field evident in the “bow shock”, the flakey outer skin of our onion above. We further have no idea why it periodically and erratically switches polarity.
2. We have no idea what is causing the crust to move.
3. We have no idea what is causing changes in oceanic and atmospheric temperature nor why these changes seem limited to a range of 6 degrees over geological time.
Generally, we are missing a lot of energy, both inside the onion and out.