Earth Anatomy for Gaeans
by Richard W. Ely
Those of us who follow Earth-centered spiritual paths need to have a scientific as well as a spiritual understanding of our planet, for Earth is our sacred text, and we should know how to read it both ways. I am fortunate in being both a professional geologist and a priest of Gaea. Most ritual circles that I attend include a grounding to establish an energetic connection with the Earth. Groundings are, in principle, a Good Thing, but I sometimes find my inner critic is so aroused by the uninformed, vaporous imaginings of what lies beneath our feet that I must tune out the words out and do my own grounding. In self defense, I offer this basic outline of Earth's inner anatomy.
First some history. Earth accumulated, along with the sun and other planets, about 4.5 billion years ago out of a whirling, collapsing cloud of interstellar gas and dust. The collapse of this cloud probably was triggered by a nearby supernova, which also synthesized nearly all of the iron and denser elements in the solar system. Earth itself appears to have accreted largely from a swarm of cold, solid bodies, which ranged in size from grains of dust to larger than the planet mars. The late stages of Earth's accretion featured impacts by very large comets, meteorites and planetoids that were so energetic as to almost completely melt the proto-Earth and remove the original atmosphere.
Earth reached nearly its present size with the impact of a mars-sized body 4.5 billion years ago that was so catastrophic as to give birth to the moon. This impact probably was also responsible for the 23 degree tilt of Earth's rotation axis with respect to the orbital plane that gives rise to the seasons of the year. Although Earth had essentially reached its present diameter of 12,742 kilometers (7916 miles) by 4.5 billion years ago, the vigorous meteorite-cometary bombardment continued until about 3.8 billion years ago, periodically boiling off the oceans and expelling the atmosphere into outer space. Evidence for this has been provided by a statistical analysis of the heavily cratered surface of the moon and dating of geologic specimens returned from the moon.
Earth's two outer layers, the atmosphere and hydrosphere, thus were born from the waning stages of the rain of comets and meteorites, which continued to fall long after Earth had reached 99 percent of its present size. Only a small portion of Earth's present atmosphere and hydrosphere are thought to have been derived from volcanic outgassing from the interior.
The deep structure of the Earth has been investigated primarily using seismic waves, which have two principal types: P (pressure) waves, where the vibration is back and forth in the direction of propagation, and S (shear) waves, where the vibration is perpendicular to the direction of propagation. S waves can only propagate through solids. An S wave can be induced in a solid object such as a steel bar by striking a glancing blow against one end. P waves can travel through molten as well as solid portions of the Earth, and have a velocity that is almost twice as fast as that of an S wave in the same material (sound is a P wave). The reflections, refractions and abrupt velocity changes with depth of these seismic waves provide the basic scientific information about Earth's inner anatomy. In recent years, three dimensional images of the variations in seismic-wave velocities have been obtained using acoustic tomography, a technique similar in principle to the CAT scans used by physicians to image the body's interior.
Deep Earth conditions can now be simulated in the laboratory using a diamond-anvil pressure cell. The heart of this apparatus consists of two large gem-quality diamonds with flat tips. A mineralogical sample and a surrounding gasket are placed between the tips of the diamond anvils, which are then pressed together and the sample heated with a laser beam that shines through the diamonds. The emerging laser beam also provides information on the chemical reactions that are occurring in the sample. The solid Earth has three primary subdivisions that are defined by differences in composition. These are the crust, the mantle and the core. Although these terms are known by most literate people, the discussion that follows will necessarily present some additional names that will be unfamiliar to many. However, I have attempted to keep the scientific jargon to a minimum - think of it as learning the names of the organs and processes within a body different from your own. In addition, many of the concepts and terminology are not universally agreed upon, especially so because we are in a time of rapidly evolving understanding of Earth's interior. The information I am providing is not 'cast in stone' so to speak, but rather a middle-of-the-road view of current geologic knowledge.
Lithosphere is a term that has been used in a variety of ways by different authors. I will use it to refer to the part of the Earth that behaves in an elastic manner, i.e. when deformed it will return to its original shape after the stress is removed, as will a rubber band. For example, 10.000 years after the continental ice sheet melted, the lithosphere of the Canadian shield is still rebounding from the weight of the glacier that weighed it down for 100,000 years. The lithosphere includes the crust and the uppermost part of the mantle. Below the lithosphere, the mantle rock is a viscous solid that deforms plastically when stressed, but will not return to its original shape when the stress is removed (silly putty is an example of a viscous solid). An important thing to remember is that there is very little actual molten rock within the crust and mantle, otherwise S waves could not pass through.
The crust extends down to a depth of 10-12 km (6-7 miles) under most ocean basins, and 30-50 km (20-30 miles) under most continents. The base of the crust is marked worldwide by an abrupt increase in seismic wave velocities, the Mohorovicic discontinuity (the moho for short), which is thought to mark a change in bulk composition to the denser rocks of Earth's mantle that are mostly made up of olivine, an iron-magnesium silicate mineral.
The oceanic crust is largely made up of submarine basalt flows that were extruded along mid-ocean ridges, shallowly emplaced igneous intrusives and a relatively thin overlying layer of sediments. Oceanic crust is much younger than continental crust, because it is constantly sinking back into the mantle along subduction zones and being renewed by sea-floor spreading at the mid-ocean ridges. Based on current rates of sea-floor spreading, Earth's oceanic crust has been completely subducted and replaced about 30 times in the last 4 billion years. The oldest known oceanic crust is under the western Pacific and is less than 200-250 million years old.
Continental crust is essentially a low-density slag that has been exuded from Earth's mantle and is enriched in silicon, aluminum, oxygen and heat-producing radioactive elements. The continents resist subduction, because they float on the underlying, dense mantle and are physically strong. The oldest rocks discovered to date on Earth are from northern Canada and are 3.96 billion years old. Contrary to the old advertising slogan, it is zircons, not diamonds, that are forever (diamonds, being made of carbon, will burn). Zircon crystals that have been recovered from metamorphic rocks in Australia are about 4.3 billion years old, dating from the time of the meteorite bombardment. These are the oldest known, intact, physical objects that formed on the Earth. The oldest objects identified to date on Earth are minuscule, metallic-oxide grains found inside some meteorites, which are about 6 billion years old and formed inside a now vanished red-giant star.
The crust also is, in general, the brittle portion of the Earth that is capable of fracturing and producing earthquakes. The high temperature and pressure below the crust make brittle failure impossible below a certain depth, the precise value of which depends upon the local temperature and composition of the rock. The oldest portions of the continents have deep keels below the lithosphere that extend down to depths of 200 to 400 km (125 to 250 miles), which have persisted for over a billion years. These deep continental roots are sometimes referred to as the tectosphere.
It is normal to think of the Earth as being hard, for we are small and that is our experience. However, compared to its size, Earth is soft and weak. Imagine that the planet has been shrunk so that you could easily hold it in your hands, and that the strength has been scaled down as well. It would feel like a balloon full of mayonnaise. The balloon is analogous to the lithosphere, the mayonnaise to the mantle. To make the analogy more complete, the balloon should be wet, to simulate the oceans, and covered with brittle paint to simulate the crust. The earth is so weak that cavities cannot exist at great depths greater than a mile or two, for rock cannot support much greater overburden, and plastic deformation would soon close up any cavities below the lithosphere. So much for the myth of the hollow Earth, long a favorite in extreme right wing circles.
Underlying the lithosphere is the asthenosphere, the weakest portion of the mantle. The weakest part of the asthenosphere is the seismic low-velocity zone, which is present at the top of the asthenosphere in most areas, extending to a depth of about 45 km (30 miles) below the bottoms of the lithospheric plates. The low-velocity layer is very weak compared to the material above and below, and the overlying lithospheric plates slide over it or sink through it with relative ease. The asthenosphere probably contains 1 to 2 percent melt, rather like an extremely hot and dense snow cone. Note that molten rock is nearly absent from the mantle. The mantle flows in a plastic manner through recrystallization and creeping dislocations in the crystalline grains.
The base of the asthenosphere is variously put at 220 to 400 km (140 to 250 miles) where the transition zone begins and extends to a depth of 660 km (410 miles). The transition zone is a region where the speed of seismic waves increases rapidly with depth. Laboratory experiments with diamond-anvil pressure cells indicate that olivine recrystallizes to denser mineral phases at pressures and temperatures coincident with seismic wave discontinuities at depths of 400 km (250 miles) and 660 km (410 miles).
The deepest earthquakes occur in the relatively cold, subducted slabs of oceanic lithosphere that sink to the bottom of the transition zone and appear to pile up for a time at the 660 km discontinuity before warming up enough to recrystallize to denser minerals and then sink to the bottom of the lower mantle. The lower mantle is thought to almost entirely consist of the minerals perovskite and periclase, which together are the chemical equivalent of olivine. Because of the enormous pressures in the mantle, the olivine crystal lattice is too weak to support itself below 660 km, and recrystallizes into the denser minerals.
The basal portion of the mantle, called the D'' layer by seismologists, has been the focus of considerable interest in recent years. The D'' layer is studied by focusing on a certain class of seismic waves that have been refracted above the upper surface of the core. The D'' layer is about 300 kilometers thick and overlies the liquid metal of the outer core. Recent studies of the D'' layer have revealed parts of it to be a graveyard of sunken slabs of oceanic lithosphere that have slowly drifted down through the mantle to come to rest on the liquid core. These slabs have piled up to form anti-continents that are the opposites of the ones we dwell upon, having sunk to the bottom of the mantle instead of floating on top. Surrounding these anti-continents are seismic-wave ultralow-velocity zones where about half of the rock volume probably is molten. These anti-oceans of magma crystal slush are the roots of long, narrow magma plumes that rise to the base of the lithosphere and feed hot-spot volcanoes such as Hawaii and Iceland. Here then is the physical manifestation of Tartarus, the mythic realm below Hades, where the first gods were banished by the gods of Olympus. This is a land where anti-continents float on liquid metal underneath a silicate sky, bordered by seas of magma from which rise 2,000 mile long columns of molten rock connecting that shadow realm with ours. Is it no wonder, then, that chthonic energies are so strong at volcanoes?.
Earth's core has a radius of 3470 km (2155 miles), which corresponds to a depth of 2900 km (1,800 miles). It is thought to be about 90 percent metallic iron, 9 percent nickel, and 1 percent sulfur and other nonmetallic elements. The outer core is known to be molten, because S waves do not pass through it, and is believed to flow in huge convection cells that are an important part of the geodynamo that generates Earth's magnetic field.
The inner core is crystalline iron, with a radius of 1,220 km (760 miles). P waves move measurably faster through the inner core in a north-south direction than across it. This is thought to be due to two factors: a precise parallel orientation of the iron crystals of the inner core, coupled with the fact that P waves travel faster along the principal-axis of crystallographic symmetry of an iron crystal than they do perpendicular to the axis. In fact, many geophysicists believe the inner core is a single gigantic crystal of iron. Talk about your crystal magic, Mama's got a big one. Either way, one crystal or many, the inner core has crystallized with its principal crystallographic axis oriented nearly north south. Consequently, the seismic waves that follow this axis arrive sooner than would otherwise be expected if the inner core were made up of randomly oriented crystals. Furthermore, the maximum seismic-velocity axis is tilted about 10 degrees relative to Earth's rotation axis, allowing seismologists to identify a slow eastward motion of this feature, such that it rotates once every 400 years relative to Earth's surface.
Several explanations for the motion of the inner core are possible, but the one I favor is deceleration of the Earth due to tidal friction. Ocean tides and tidal flexing of Earth's surface cause slight frictional heating, just as a coat hanger will heat if you bend it repeatedly. The solid Earth has tides that amount to about 0.6 meters (2 feet) of twice-daily vertical movement near the equator, decreasing towards the poles. The energy for the frictional heating is derived from the kinetic energy of the rotating Earth, causing the Earth's spin rate to slow down.
Study of ancient tidally influenced sediments has revealed that the length of the day was about 18 hours long 900 million years ago. Another effect of tidal friction is to transfer some of the angular momentum of the Earth's rotation to the moon, so that the radius of the moon's orbit enlarges by 3.82 cm a year (as measured by laser ranging of instruments left on the moon by the Apollo astronauts). The enlargement of the moon's orbit has been known about for many years, as was one of the original reasons for postulating that the moon was ejected from the Earth.
Because most of the kinetic energy that is lost from friction comes from at or near the surface of the Earth, it is the lithosphere that slows down the most, causing it to drift slowly westward relative to the deep mantle, which also drifts westward relative to the core. Thus the inner core, which is buffered from these effects by the liquid outer core, spins the fastest.
In conclusion, I offer here a full dress grounding such as I might do at my home in western Sonoma County. First, stand with your feet at shoulder width, press them into the ground, feel the solid Earth that supports you, honor the Earth. Now, center yourself in your body in your heart chakra. Establish a strong connection with your field of love and then will your energy to descend through your lower chakras, down your legs and into the soil. Know that the soil is teeming with life. Thank the soil for sustaining us and then will your energy to descend further, perhaps imagining it as twin red cords that spiral around each other as they emerge from your feet. Below the soil is a soft, fossiliferous marine sand, filled with fresh water. Know that this sand was deposited in the precursor to San Francisco Bay, gone for 2,000,000 years. Feel the presence of that ocean water lingering in the rocks, the spirit in the fossils, and realize that these sands accumulated when our ancestors first learned the use of fire.
Will your energy to descend further, and a mere 30 feet down we come to the ancient rocks of the Franciscan Complex, a disordered mixture of various oceanic rocks that were bulldozed up by the westward-drifting North American continent during the time of the Dinosaurs. These rocks are the quintessence of pure, solidified chaos - hail Eris, Coyote and Raven. Will your energy to descend further, and 10 miles or so down we leave the Franciscan Complex, pass through a great horizontal fault and enter the mantle. The rocks grow hotter and softer as your energy descends, and at a depth of several tens of miles they are hot enough to glow with a red Hadean light. Do not fear, and will your energy to descend further, passing ever downward into hotter, denser rocks that glow yellow then white, coming eventually to Tartarus at the base of the mantle, the shadow realm where the old gods were banished.
Pause here if it is your will, and connect your energy with whatever powers you find compatible, then descend through the roiling liquid metal of the outer core to come to the great crystal, the icon of the Central Realm of the Densely Packed. If it is your will, bind your energy to that great crystal, and honor it as the heart of Mother Earth.
Now, return up the path you descended, bringing a cord of energy that is connected to the heart of Mother Earth, passing in reverse order all of the places you experienced on the way down, coming at last to your own body, centered in your heart. With your heart energy joined with the heart energy of the Earth, will the combined energies to rise through your upper chakras, emerging from your crown to rise to the cosmic heights, to Heaven above, a fountain of love. Let the lower and upper energies mingle for a time, and then call them down, back into your heart center, where you should pause and cherish them. Then will the energies to descend down into the core of the Earth, while you stand as the World Tree stands, a bridge connecting the Great Above with the Great Below. So be it.
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