User:Mmcannis/sandbox/Earth's surface evolution

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An overview of Earth evolution covers 4.56 billion years of Earth history. It not only provides the basis for the origin of life on earth, but with basic histories of plate tectonics, continental drift, ice ages, climate and ocean current changes, is the setting for an active history of earth. The evolution involves life, geology, ice science of glaciation and ice ages, volcanism, continent and ocean building, to name just a few major topics.

Through mountain formation, volcanism, climate changes, by various mechanisms including earth axis tilt, or new ocean currents because of landform removals or additions, climate changes as well as speciation are in constant adjustment. Examples of desertification are only incidentally caused by humans; evolving regional changes to deserts, and desertification, are more properly related to climate, wind patterns, continental changes from movement to new longitudes and latitudes over geologic timescales, often steady, but sometimes altered to becoming super fast, (the Indian Subcontinent), or exceedingly stable, (the North American Laurentian shield of Canada, altered to large regional flatness through glaciation).

This article will focus on Earth's surface evolution, the atmosphere, continents, oceans and the crust (geology); for a discussion and timeline of Earth's interior, see Earth and Structure of the Earth.

Globally for earth's surface, the 4.56 billion year history is an interplay of ocean, water, temperature, chemistry, atmosphere, minerals, floating continents, and tectonics. Non-earth surface sources of sun temperature, axis tilt, and earth orbital variations-(cycles), with earth's climate variations are also factors. Other factors below the earth's surface are from crust (geology) and lithosphere changes and their effects upon earth's surface.

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Evolution of the pre-continent Earth surface
With continent creation only covering the last fourth of Earth's suface evolution history, some major topics and disciplines must also be brought to the forefront. A short list includes, Evolution of Earth's atmosphere; rock and mineral creation, (diagenesis refers to creation of rock types after minerals are deposited geologically or oceanographically); water, ice, and ocean evolution of the pre-continent earth; and a discussion of proto-climatology and Earth's wind structure.

Ocean evolution
At a certain point in the creation of rock types, dissolved elemental Potassium, (K) was removed from the ocean and incorporated into rock types; (a similar concentration to sodium, Na, in the earth's surface).

Creation of lighter continental rock & single-cell life
The oldest rocks are incorporated in only scattered areas of continents, and only small areas of a few continents contain the actual remnants of the proto-continents. Single cell life, from about 3.4-3.2 billion ya is also found only in specific rock layers, on specific continents.

Plate tectonics
Plate tectonics has driven the present ocean shapes, continent movement, and the extensive regions of ocean ridges and oceanic trenches. The earth is like an ornate and complex ridged baseball, with the sewn thread seam (=mid-ocean ridges, or other, the spreading centers), running in various directions, with intricate connections, and endings, as well as also disappearing into continents, or having their creation in specific locales, either continental, or oceanic. The oceanic trenches typically also created mountain chains, and continental margins. But plate tectonics was in progress in the first half of earth's history before the proto-continents. Planet Venus, closer to the Sun, and hotter, may be considered an equivalent-type tectonic analogue; both planets may have much of the early surface reworked. On Earth, some examples of specific, old, specialized mineral-types may give clues to the early evolution of rocks or rock layers in the Neoarchean. Diamonds, carbon (C), formed at high pressure in the upper lithosphere would be one specialized 'rock' type example, having been formed under high pressure in mostly vertical dikes. Yellow uranium (ore) is also typically found in vertical dikes.

The movement of continents on earth has left continents spread relatively even over the planet's surface, but with more than half of the world still covered by oceans, about 65 percent. The continents appear static, with a South Pole-centered Antarctica a revolving point, with the Antarctic Circumpolar Current driving currents around the continents, at the extreme south of the Southern Hemisphere, and with large amounts of ice covering the Antarctic continent, that are stable today, and in geologic terms, has been a sustained continental ice sheet for some millions of years.

Since the oldest ocean floor surface can be found in the west of Earth's largest plate, the Pacific Plate, 145 to 137 years old, but with continents containing rocks that have ages back into the Proterozoic of 3.5 billion years, the easy conclusion is that plate dynamics continue to actively modify oceans especially, and certain regions of continents. A specific example of high-speed activity is the rapid raising of the Himalaya Mountains by the Indian Subcontinent; the seafloor associated with its rapid movement shows oceanographic landforms related to that movement across the Indian Ocean

Earth's crust
The crust of the earth is the main expression of earth's present day surface features, and includes the oceans and the unseen ocean forms. A large topic of physical oceanography drives many of former and present day landforms and their continued changes.

Volcanism
Though plate tectonics, ocean evolution, and physical oceanography shape the surface expression of the earth's crust, besides mass added to earth from meteoric sources, volcanism is clearly the major component of surface land, (or underwater land) being created &mdash; (the other major crustal additions are either at spreading centers, or earth mantle plume-based additions); volcanism is usually associated with continent margins, or fault zones, and therefore also locally affected by earthquakes which in themselves, do local physical evolution to continental rock. Besides actual volcanoes, or volcanic mountain chains, or hotspot (geology) activity, surface or below-surface expressed, volcanism can leave regional alterations, for example the Deccan Traps. Below surface, continental volcanism of laccoliths and batholiths are also local, or regional evolution steps, that are mostly easily timestamped, in earth's evolution.

Life on land and sea
Life in the world's oceans began before continents, and continued later upon the earth's land masses. The combination of ocean chemistry, also an evolving atmosphere, and a seafloor and continents in constant movement, led to active interaction between geological forces, and elemental evolution of water chemistry, and especially the atmosphere of earth. A beginning non-oxygen atmosphere was over time, turned into an oxygen-based atmosphere, and then able to sustain a new suite of animal and plant life. The chemical removal of the banded iron formation, now harvested for its iron, (Fe) was laid down geologically, and essentially was the rusting out of available Fe from the surface of earth, as well as all soluble available areas.

Abbreviated earth evolution timeline
An abbreviated timeline:


 * –ca 3.4-3.2 Ba, cellular life forms
 * –1100-750 Ma, proto-continents, (Proterozoic, continent Rodinia, 1100-750 Ma)
 * –ca 635 Ma, Ediacara biota, (then Cambrian explosion), the major Biological evolution start point
 * –250 Ma, start of Pangaea breakup
 * –65 Ma, ~End of Dinosaurs, Chicxulub Crater, K-T Boundary
 * –65 Ma, Age of Mammals, Age of the Grasses (Angiosperms)
 * –ca 5.5 Ma, Human evolution

Dating, timestamping, correlation markers
Dating of earth evolution events aids in understanding the pathways that the subsystems of the earth passed through. Coring of ocean sediments, or conversely on continents, in lakes, or dry land regions, from steppes to desert-based bajadas, can reveal organisms, geological movements of material, or even animal (fossils), or plant species by pollen, (palynology).

Various rock types have dating abilities of their constituents, or even magnetic pole timestamps, that can aid in understanding initial local deposition, or later relocations of rock groups. Sedimentary rocks have a history of inclusions, as well as explaining isostatic loading of geologic layers, with effects on neighboring geologic layers.

For biological evolution timeperiods, (from the Ediacara biota-Cambrian explosion beginnings), animals, plants, and microscopic life have all aided reference to timeperiod knowledge. A famous example for ocean research are the foraminifera, whose unicellilar skelatal bodies sink to the seafloor, and yield knowledge of ocean parameters, for example oxygenation, and implications to atmosphere constituency, as well as ocean oxygen levels.

Glaciology
Glaciology as the encompassing field for mountain glaciers, continental glaciers and major ice sheets, easily yields a record of snow-ice deposition, as well as clues to climate change, both for the entire earth (macroscopically), or in local regions. The layers inside glaciers record readable, timestamped conditions; even locusts in North America have preserved the recent extinction of the Rocky Mountain locust in two Grasshopper Glaciers. Glaciers, mountain glaciers and ice sheets also alter surface geography. Winds blowing on glacier margins also contained windblown material, a specific example being the loess deposits of central-northern China during ice ages. Another dramatic example of North American evolution is the Channeled Scablands formed from cyclic ice dam collapses from glacial Lake Missoula.

Antarctic Ice Sheet
The Antarctic Ice Sheet as a stable ice sheet since Antarctica located its continental position at the South Pole, contains a deep, columnar history of earth since the continents location. Coring can yield entrained gas concentrations through the entire coring column, and thus give reference data to atmosphere and climate changes through that time period. Inclusions of particulates, and/ or pollen, windblown dust, volcanic output material, and other entrained items, all yield correlation markers to events that can happen on a global scale. Supervolcanos will yield not only particulates or aerosols, but also thickness changes in the layers of snow-ice that are readable. Analysis of the historical ice column also has a relationship to the present Antarctic ice shelf which is undergoing recent shrinkage and breakup.

The Baffin Island glacier and Greenland are the two remaing glacial "ice sheets" in the Northern Hemisphere.

Glaciers and meteorites
Glaciers also have a unique ability to collect meteorites. Melting glaciers, or more specifically end moraines contain the deposited material load of rock and debris, but can contain meteorites. Other areas, when the glacier retreats/melts may leave a uniform surface, but with the meteorites easily observable. The meteoric activity may be read in a timeline, and may also give some relationahips to recent earth atmosphere history (the glaciers or ice sheets, are recent evolutionary events).

Abbreviated list of some evolved earth features
Abbreviated list.

Features evolving out of equilibrium
Earth features undergoing change, requiring discussion, debate, or research.