#plutonism

Robert J. Hay Cunningham – Scientist of the Day

Robert James Hay Cunningham, a Scottish geologist, died May 15, 1848; one source says he was just 27 years old at the time of his death, which I doubt, because we are going to discuss a book of his, published in 1838, that could hardly have been the work of a 17-year-old. 

James Hutton – Scientist of the Day

James Hutton, a Scottish geologist, was born June 14, 1726, in Edinburgh. 

Alberto Fortis – Scientist of the Day

Alberto Fortis, an Italian geologist, was born on Nov. 9 or 11, 1741.

George Steuart Mackenzie – Scientist of the Day

George Steuart Mackenzie, a Scottish geologist, was born June 22, 1780.

John Playfair – Scientist of the Day

John Playfair, a Scottish natural philosopher, was born Mar. 10, 1748, near Dundee.

One of my more abstract Geology papers: (Needs editing)

Deep Geologic Time

Deep geologic time has to do with events in the remote past.  It could be considered the time spanning the formation of solid rocks, meteors and planets in our solar system, to the end of the last ice age approximately 10,000 years ago.  The latter may not be commonly thought of as deep time but may be included in the argument since it is the last major semi-global event that affected the state of geology and geomorphology in certain regions today, through the carving of portions of continents by the expansion and recession of glaciers and ice sheets.  If that marks the end of deep time, the beginning is the time when dust and gases in the solar system accreted into larger solid objects such as meteors and comets and subsequently these larger objects through the force of gravity accreted to form the planet Earth.  The oldest period of deep time, associated with the youngest earth, is known as the Hadean age, when pressure, friction and radioactive decay, resulted in the melting of rocks, the release of gases, the sinking of heavier molten metals to the core, and the beginning of the Earth’s inner furnace.  Evidence of the time scale of the earth has developed over the past few centuries culminating in highly sophisticated geochronologic controls such isotopic dating.  The current age of the earth has been determined by measuring Pb ratios in red clay and manganese nodules from the floor of the Pacific Ocean. 

It is widely accepted that these samples contain an average of all the earth’s lead.  Plotting the radiogenic lead Pb207/Pb204 against the primeval lead Pb206/Pb204 gives an approximate age of 4.5 billion years.  This age matches the oldest iron and stony meteorites found on earth (3).  This suggests that the earth formed at a similar time to other rocky material in the solar system including terrestrial planets.  

              The concept of deep time first became popular in the 18th century.  A popular school of thought termed Neptunism, spawning from the theories of Abraham Werner, took hold in scientific circles in the late 18th century.  Neptunistic theories proposed that in the past the entire earth was covered by a primitive ocean that held vast amounts of dissolved material.  This ocean receded turbulently in places and precipitated in place what are today’s continents (1). 

Complimenting this idea was the theory that there was no internal fire in the earth (1). 

Neptunism considered granite, basalt and other igneous rocks to be all deposited by water (1). 

Neptunism did however have a stratigraphic sequence with granite being the first to deposit,

“followed by metamorphic rocks, chemical precipitates, and other series of strata as the water fell” (2).  The granite and metamorphic rocks such as gneiss and schist were labeled Primitive strata.  The next layer was mainly chemical precipitates with some mechanical deposits, labeled the Transitional strata.  The next layer or the Floetz strata, held mainly mechanical deposited sediments which included fossils (3).  On top were alluvial deposits which were deposited in

“lowland areas, having only local distribution, and derived from mechanical weathering of older rocks”(3).  Observable inclined strata were attributed to chemical precipitates.  They were explained with the fact that precipitates sometimes crystallize on the sides of objects.  In other cases they were solidifications of unconsolidated sediments slipping down slopes and then cementing together (3).  The idea of uplift was not considered in Neptunism.  Mountains and valleys were produce by the turbulent subsidence of the primitive ocean cutting deep channels (3).  Other geologic aspects considered by neptunism were out of sequence strata that developed when the primitive ocean refilled to certain heights and deposited material above older material.  Volcanoes were considered a product of combustion of underlying seams of coal (3).  While today many of these views seem unlikely, one theory that has stood the test of time, is the suggestion that sediments were lithified by layers of mineral cementation (3). 

            While the essence of neptunism is water, the essence of plutonism is fire.  The idea of plutonism, made popular by geologist James Hutton in the late 18th century, proposed that heat is behind the forces of the earth.  Plutonists believed that a system of heat from the earth’s interior caused uplift of the land.  This explained marine fossils on land.  The uplifted land was eroded and sediments were deposited into the sea, thereby compacted by heat, pressure and depth, and thus the cycle was repeated (3).  Volcanoes were evidence of the subterranean furnace below the earth, and produced intrusive igneous rocks such as granite and basalt.  Hutton’s plutonistic theories led to the understanding of angular unconformities.  These unconformities were recognized as the evidence of a “sequence of deposition, consolidation, tilting, uplift, erosion, deposition and consolidation”(3).  The idea of all these processes occurring in a sequence at a rate of occurrence is central to the idea of uniformitarianism.