Supercontinent cycles and their ecological and climatic effects on animal and human populations

Supercontinent Theory

The physical geology of the earth consists of a Core (inner and outer), the mantle, the asthenosphere and the lithosphere. The lithosphere is the crust and upper mantle of the earth that is the hard and rigid layer in which humans live. This portion of the earth reacts to the atmosphere, hydrosphere and biosphere through erosion and weathering, resulting in the soil forming process (Johnson, 2006). These layers of the earth are constantly in motion, giving us the Plate Tectonics, or Continental Drift, theory. Briefly, the theory states that the continents move across the molten plate of the earth -- drifting over time based on the rotation of the earth. The early evidence for this, of course, was that the eastern part of South America and Western Part of Africa fit together quite well. However, studies after 1958 show that there are three major reasons why the "drift" theory is likely incorrect: 1) floating masses on a rotating ball tend to collect at the equator and remain there; 2) masses floating like icebergs should be in balance with gravity and buoyancy whereas measurements show this is not the case, and; 3) why were some parts of the Earth solid while other parts are fluid. Thus, Plate Tectonics agrees that the earth's lithosphere is in movement, but rather than drifting, move based on plate dynamics that are influenced by natural processes like earthquakes, volcanoes, and mountain building. Several forces drive this theory: friction (motion between layers); gravitation -- sliding at higher elevation of plates and bulging at lower; 3) external forces (tidal friction of the moon). Plate tectonics is less random, and accepts that there are several forces acting in opposition to cause change and movement (USGS, 2009).

The Supercontinent Cycle is the manner in which the continental crust of the earth moves and thus the continents reconfigured, in cycles scientists estimate to take 300-500 million years. The cycle consists of collusion and rifting; collision makes fewer and larger continents and rifting makes more, but smaller continents. For instance, the last supercontinent called Pangaea, formed about 300 million years ago and we can see the manner in which the geologic forms split during five major shifts -- expansion and then collision, to form the present-day continents (see Figure 1).

Most believe the causes of this type of grand movement are volcanism, which is a continual process in which the plates of the earth move, twist, sink or rise. The point is to understand that there are driving forces, like seafloor spreading, that cause continual movement; perhaps slow in human time, but relatively quick in geological time. The theory of Sea-Floor spreading accounts for the age of the sea-floor and its movement, working together with the idea of plate tectonics. The movement of the seafloor is quite similar to that of a conveyer belt in that it moves away from the mid-oceanic ridge across the basin and then into continents. It is the result of slow and steady movement in a way that focuses the high heat from the seafloor to act with the relatively young sea rocks to push spreading outward from mid-ocean. This continual process causes the sea-floor to be relatively new (younger rock) and the old sea-floor is continually being destroyed near trenches -- the new sea-floor built up along ridges. The increase in age comes as rocks move away from ridges -- so that the youngest part of the sea-floor is constantly moving towards the continents as it ages. We can also think of it as a steam kettle from the core of the earth -- as magma and heat rise to the ocean's bottom, new rock is born. Then, as movement occurs towards the continent, continual new rock moves the older rock, so that when it finally gets to the Continent, it is far older (Frankel, 2012, Intro).