The tectonic plates of the world were mapped in the second half of the 20th century. Remnants of the Farallon Plate, deep in Earth's mantle. It is thought that much of the plate initially went under North America (particularly the western United States and southwest Canada) at a very shallow angle, creating much of the mountainous terrain in the area (particularly the southern Rocky Mountains). Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a scientific theory that describes the large-scale motion of Earth's lithosphere. This theoretical model builds on the concept of continental drift which was developed during the first few decades of the 20th century. The geoscientific community accepted the theory after the concepts of seafloor spreading were later developed in the late 1950s and early 1960s. Key principles The outer layers of the Earth are divided into the lithosphere and asthenosphere. Types of plate boundaries
Related: Mesoproterozoic era
Grenville orogenyExtent (orange regions) of the Grenville orogeny, after Tollo et al. (2004) and Darabi (2004). Timescale The problem of timing the Grenville Orogeny is an area of some contention today. Timeline of the Grenville orogeny, after Rivers (2002) Ages are approximated from the magmatic activity associated with the individual cycles of the orogeny. River’s 2008 paper has now examined the timing of the different periods of the orogeny and reconstructed the timeline based on the spatial and temporal metamorphism of the rocks present. General Tectonics Reconstruction of the events of the orogeny is ongoing, but the generally-accepted view is that the eastern and southern margins of Laurentia were active convergent margins until the beginning of continental collision. General Lithology The Grenville Orogeny can be categorized into three sections based on structure, lithology, and thermochronology. The age of this belt is approximately 1.8 to 1.18 Ga. Regional Variations
Earth l Earth facts, pictures and information.Earth is the third planet from the Sun and the fifth largest: Planet Profile orbit: 149,600,000 km (1.00 AU) from Sundiameter: 12,756.3 kmmass: 5.972e24 kg History of Earth Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet. Earth, of course, can be studied without the aid of spacecraft. The Earth is divided into several layers which have distinct chemical and seismic properties (depths in km): 0- 40 Crust 40- 400 Upper mantle 400- 650 Transition region 650-2700 Lower mantle 2700-2890 D'' layer 2890-5150 Outer core 5150-6378 Inner core The crust varies considerably in thickness, it is thinner under the oceans, thicker under the continents. atmosphere = 0.0000051 oceans = 0.0014 crust = 0.026 mantle = 4.043 outer core = 1.835 inner core = 0.09675 Earth's Satellite Open Issues
StromatoliteMorphology Fossil record Archean Some Archean rock formations show macroscopic similarity to modern microbial structures, leading to the inference that these structures represent evidence of ancient life; namely stromatolites. However others regard these patterns as having been due to natural material deposition or other mechanism, and thus abiogenic. Younger Stromatolites in the Hoyt Limestone (Cambrian) exposed at Lester Park, near Saratoga Springs, New York. Stromatolites (Pika Formation, Middle Cambrian) near Helen Lake, Banff National Park, Canada Stromatolites are a major constituent of the fossil record for about the first 3.5 billion years of life on earth, peaking about 1.25 billion years ago. They subsequently declined in abundance and diversity, and by the start of the Cambrian had fallen to 20% of their peak. Proterozoic stromatolite fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). Modern occurrence
Earth's magnetic fieldComputer simulation of the Earth's field in a period of normal polarity between reversals. The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core. The North Magnetic Pole wanders sufficiently slowly to keep ordinary compasses useful for navigation. The magnetosphere is the region above the ionosphere and extends several tens of thousands of kilometers into space, protecting the Earth from cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation. Importance Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the North Magnetic Pole does shift with time, this wandering is slow enough that a simple compass remains useful for navigation.
SedimentSediment billowing out from Italy's shore into the Adriatic Sea Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice, and/or by the force of gravity acting on the particle itself. Sediments are most often transported by water (fluvial processes), wind (aeolian processes) and glaciers. Classification Grain size Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder". Composition Composition of sediment can be measured in terms of: This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals). Sediment transport Sediment builds up on human-made breakwaters because they reduce the speed of water flow, so the stream cannot carry as much sediment load. Glacial transport of boulders. Particle motion where Fluvial bedforms
Swarm reveals Earth’s changing magnetism -- ScienceDailyThe first set of high-resolution results from ESA's three-satellite Swarm constellation reveals the most recent changes in the magnetic field that protects our planet. Launched in November 2013, Swarm is providing unprecedented insights into the complex workings of Earth's magnetic field, which safeguards us from the bombarding cosmic radiation and charged particles. Measurements made over the past six months confirm the general trend of the field's weakening, with the most dramatic declines over the Western Hemisphere. But in other areas, such as the southern Indian Ocean, the magnetic field has strengthened since January. The latest measurements also confirm the movement of magnetic North towards Siberia. These changes are based on the magnetic signals stemming from Earth's core. This will provide new insight into many natural processes, from those occurring deep inside our planet to space weather triggered by solar activity.
MesoproterozoicThis era is marked by the further development of continental plates and plate tectonics. The first large-scale mountain building episode, the Grenville Orogeny, for which extensive evidence still survives, happened in this period. This era was the high point of the Stromatolites before they declined in the Neoproterozoic. The era saw the development of sexual reproduction, which greatly increased the complexity of life to come. It was the start of development of communal living among organisms, the multicellular organisms. It was an Era of apparently critical, but still poorly understood, changes in the chemistry of the sea, the sediments of the earth, and the composition of the air. Subdivisions The subdivisions of the Mesoproterozoic are arbitrary divisions based on time. By contrast, the transition from Calymmian to Ectasian has no meaning beyond calendar time. For that matter, they are not completely without biological markers. References Jump up ^ U. External links