Large-scale Geophysical cycles recur at comparatively slow time rates, with periods ranging from several seconds to hundreds of millions of years.
Cycles of geophysical activity include the gradual buildup and breakdown of mountain chains, continental drift and ocean-floor spreading, volcanic activity, seismic activity and inner core shifting, glacial and interglacial periods, polar reversals, polar wandering, hydrospheric cycles including the rise and fall of sea level, and large-scale motions of the atmosphere including various weather patterns and formations.
The buildup and breakdown of continental mountain ranges have predictable oscillations which occur in cycles of about 800 million years. Mountains originate when land masses influenced by ocean-closing movements ultimately collide, thrusting and squeezing the edges between them forming mountainous ridges flanked by continental crust.
The separation and convergence of continental land masses and ocean-floor ridges and valleys are influenced by the directions of the Earth’s magnetic field.
Continental drift and ocean-floor spreading occur at a rate of about 1 centimeter per year, 10 kilometers every million years. The rate of spreading is determined by the dating of oceanic island and ocean-floor rocks in relation to their respective distances from mid-ocean ridges.
A volume of new continental and oceanic crust accumulates at a rate of between 10 and 60 cubic kilometers per year for the oceans, and 3 cubic kilometers per year for continents.
The accumulation of lava flow from volcanic activity occurs at a rate of about 3.4 cubic kilometers per year.
5000 to 10,000 earthquakes occur every year, which range from 10 to 60 seconds in duration, and travel at a rate of 8 to 13 kilometers per second, depending on the distance of the seismic activity from the Earth’s center. The nearer the core of the Earth, the greater the density and the faster the rate of travel.
Overall, the rate of surface crust activity on the Earth is determined by the fluid motions of the Earth’s inner core, which shift about at an average rate of 1 thousand kilometers per hundred years.
Glacial and interglacial cycles produce cool and warm periods respectively, and are synchronous with various astronomical cycles.
For example, there are ice-ages which recur at about 100,000, 40,000, and 30,000-year intervals, the so-called Milankovitch cycles, which are directly linked to the orbital motions of the Earth.
The change in climate which produces these glacial periods is caused by variations in the pattern of incoming solar radiation, due to combinations of slow changes in the Earth’s orbital geometry, axial tilt, and axial wobble. When all of these motions are in phase, the result is a drop in the overall temperature of the Earth, producing an ice age. When the motions are out of phase, the result is an interglacial warming period.
Regular periods of geomagnetic field reversals recur at a rate of about one every million years, accompanied by short irregular intervals of reversal within these periods.
Following a polar reversal, the Earth’s magnetic field decreases to 15 per-cent of its normal intensity in about 10,000 years, and regains its original intensity at the same rate.
Shifting of the polar caps due to fluctuations in the inclination of the Earth’s magnetic field recurs regularly in periods of about one thousand years.
The Earth’s hydrosphere includes cycles of activity which involve ocean currents, tides, wave motions, storm systems, and surface activity which occur at various time rates depending on the forces which influence them.
Oceanic tides occur in cycles which are determined by the relative motions of the Earth, Sun, and Moon.
The oscillations and propagation of various internal and surface waves in the hydrosphere occur at rates which are influenced by various currents, as well as by the wind and other activity at the surface.
The Earth’s atmosphere produces cycles of precipitation, cloud formation, wave motions, and various storm systems, including lightning and thunder.
Lightning strikes the Earth about 100 times per second, or 3.15 billion times per year.
At any given moment, 220 thunderstorms occur on the Earth’s surface.
Large-scale disturbances of the Earth’s atmosphere and hydrosphere are caused by various weather systems and by vertical effects due to reflection and refraction, which depend on the temperature, pressure, and density of the various regions of activity, and the actions and forces which influence them.
The actions and forces which influence these motions include the Coriolis force, a rotational force which acts at right angles to the direction of the wind, moving clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Other influences include the pressure gradient force which causes pressure density changes along a direction, frictional drag acting at or near a surface boundary, divergence and convergence related to vertical flow due to reflection and refraction, centripetal acceleration related to curved flow, and diurnal, tidal, seasonal, and solar influences which cause various changes in temperature, pressure, and density at slowly evolving time rates.
The interaction of various geophysical processes produce cycles of activity which are interdependent, and which play a major role in maintaining the balance of the ecosystem over long periods.
For example, the Earth’s entire water resources are split among plant cells, and recirculated by animal and plant cells about every 2 million years. Oxygen which is generated in the process enters the atmosphere and is recycled about every 2000 years. Carbon dioxide respired by animal and plant cells enters the atmosphere and is reused again by plant cells once it has been in the atmosphere for a period of about 300 years.
The mean average of the combined rates of growth and decay of all geophysical processes has maintained a constantly fluctuating equilibrium, preserving the same overall mass, density, and temperature since the formation of the Earth.