More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Geology can also refer to the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.
Colors indicate the distribution of different rock types across the continent, as they were known then. Geology describes the structure of the Earth beneath its surface, and the processes that have shaped that structure. It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans.
Times are listed in millions of years, or megaanni Ma.
Dating of the Geologic record The Geologic record is the strata layers of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it. Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin currently estimated to have been some 4, million years ago to the present day. Radiometric dating measures the steady decay of radioactive elements in an object to determine its age.
It is used to calculate dates for the older part of the planet's geological record. The theory is very complicated but, in essence, the radioactive elements within an object decay to form isotopes of each chemical element.
The history of Earth concerns the development of planet Earth from its formation to the present day. The geological time scale GTS , as defined by international convention, depicts the large spans of time from the beginning of the Earth to the present, and its divisions chronicle some definitive events of Earth history. Ga means "billion years ago"; Ma, "million years ago".
Earth formed around 4.
Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. While the Earth was in its earliest stage Early Earth Like other SIMS instruments, the SHRIMP microprobe bombards a sample under vacuum with a beam of primary ions that sputters secondary ions that are focused, filtered, and measured according to their energy and mass. It can measure the isotopic and elemental abundances in minerals at a 30 micrometre-scale and is therefore well-suited for the analysis of complex minerals, as often found in metamorphic terrains, some igneous rocks, and for relatively rapid analysis of statistical valid sets of detrital minerals from sedimentary rocks.
The most common application of the instrument is in uranium-thorium-lead geochronology, although Hadean zircon is the oldest-surviving crustal material from the Earth's earliest geological time period, the Hadean eon, about 4 billion years ago. Zircon is a mineral that is commonly used for radiometric dating because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most igneous and metamorphic host rocks.
When the rock at the surface is buried deep in the Earth it is heated and can recrystallise or melt. The Jack Hills rocks are from the Archean eon, about 3. However, the zircon crystals there are older than the rocks that contain them. Many investigations have been carried out to find the absolute age and properties of zircon, for example the iso Most of New England consists geologically of volcanic island arcs that accreted onto the eastern edge of the Laurentian Craton in prehistoric times.
Much of the bedrock found in New England is heavily metamorphosed due to the numerous mountain building events that occurred in the region. These events culminated in the formation of Pangaea; the coastline as it exists today was created by rifting during the Jurassic and Cretaceous periods. The most recent rock layers are glacial conglomerates.
Chronology Overview The bedrock geology of New England was heavily influenced by various tectonic events that have occurred since the Paleozoic Era including the accretion of land masses that formed various continental terranes to the Mesozoic rifting of the Hartford Basin. Representative continental flood basalts also known as traps and oceanic plateaus, together forming a listing of large igneous provinces: Six String Nation was conceived by award-winning Toronto-based writer and broadcaster Jowi Taylor and designed and built by Master Luthier George Rizsanyi in Annapolis County Nova Scotia, from 64 pieces of bone, metal, wood, stone and horn.
The guitar was made as a symbol of national unity, to explore Canadian identity, and to connect people from all regions in Canada. While the impending referendum focussed on the political relationship between the province of Quebec as a francophone minority and the Canadian federal government representing an anglophone majority, Taylor sought to represent additional stakeholders within the national debate including multicultural and indigenous communities as well as francophones living outside of Queb Another fragment of Acasta gneiss Collection: Martin, Blaise Pascal University.
Contributions to Mineralogy and Petrology, v. New constraints on its tectonothermal history". Archived from the original on Member feedback about Acasta Gneiss: Geology Revolvy Brain revolvybrain. Oldest dated rocks topic A sample of gneiss from the site of the Earth's oldest dated rocks the Acasta River area of Canada. Member feedback about Oldest dated rocks: Eoarchean geology topic Eoarchean geology is the study of the oldest preserved crustal fragments of Earth during the Eoarchean era from 4 to 3.
Member feedback about Eoarchean geology: Archean Revolvy Brain revolvybrain. Slave Craton topic Geological map of north-western Canada. Member feedback about Slave Craton: Economic geology Revolvy Brain revolvybrain. Zirconian topic Zirconian Era— million years ago The Zirconian is the second Era within the Hadean Eon in a proposed revision of the Precambrian time scale. The banding is developed under high temperature and pressure conditions, the minerals are arranged into layers that appear as bands in cross section.
The appearance of layers, called compositional banding, occurs because the layers, the darker bands have relatively more mafic minerals.
The lighter bands contain relatively more felsic and these forces stretch out the rock like a plastic, and the original material is spread out into sheets. Another cause of banding is metamorphic differentiation, which separates different materials into different layers through chemical reactions, not all gneiss rocks have detectable banding.
The Acasta gneiss: Earth's oldest surface rock
In kyanite gneiss, crystals of kyanite appear as random clumps in what is mainly a plagioclase matrix, henderson gneiss is found in North Carolina and South Carolina, US, east of the Brevard Shear Zone. It has deformed into two sequential forms, the second, more warped, form is associated with the Brevard Fault, and the first deformation results from displacement to the southwest.
Most of the Outer Hebrides of Scotland have a formed from Lewisian gneiss. In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree. These rocks are igneous in origin, mixed with metamorphosed marble, quartzite and mica schist with later intrusions of basaltic dikes.
Gneisses of Archean and Proterozoic age occur in the Baltic Shield, in antiquity, gneisses were also utilized in architectural construction. Petrology, Igneous, Sedimentary and Metamorphic, 2nd ed. At a land area of approximately 1,, km2 and its estimated population as of is 44, Yellowknife became the capital in , following recommendations by the Carrothers Commission.
The Northwest Territories are bordered by Canadas two other territories, Nunavut to the east and Yukon to the west, and by the provinces of British Columbia, Alberta, and Saskatchewan to the south. The name is descriptive, adopted by the British government during the era to indicate where it lay in relation to Ruperts Land. There was some discussion of changing the name of the Northwest Territories after the splitting off of Nunavut, one proposal was Denendeh, as advocated by the former premier Stephen Kakfwi, among others. One of the most popular proposals for a new name — one to name the territory Bob — began as a prank, in the end a poll conducted prior to division showed that strong support remained to keep the name Northwest Territories.
This name arguably became more appropriate following division than it had been when the territories extended far into Canadas north-central and it possibly meets Manitoba at a quadripoint to the extreme southeast, though surveys have not been completed. It has an area of 1,, km2. The Northwest Territories extends for more than 1,, km2 and has a large climate variant from south to north, the southern part of the territory has a subarctic climate, while the islands and northern coast have a polar climate.
Summers in the north are short and cool, with highs in the mid teens Celsius. In the north they are rare, but do occur. Tornadoes are extremely rare but have happened with the most notable one happening just outside Yellowknife that destroyed a communications tower, the Territory has a fairly dry climate due to the mountains in the west. Yellowknife — Yellowknife is the capital and only city, as well as the largest community in the Northwest Territories, Canada.
The current population is ethnically mixed, of the eleven official languages of the Northwest Territories, five are spoken in significant numbers in Yellowknife, Dene Suline, Dogrib, South and North Slavey, English, and French. Yellowknife quickly became the centre of activity in the NWT. As gold production began to wane, Yellowknife shifted from being a town to a centre of government services in the s. However, with the discovery of diamonds north of Yellowknife in , traditionally, First Nations people of Yellowknives Dene culture had occupied this region, by the s they had a settlement on a point of land on the east side of Yellowknife Bay, Dettah.
The current municipal area of Yellowknife was occupied by prospectors who ventured into the region in the mids, blakeney, made the first discovery of gold in the Yellowknife Bay area in The discovery was viewed as unimportant in those days because of the Klondike Gold Rush, in the late s, aircraft were first used to explore Canadas Arctic regions.
Samples of uranium and silver were uncovered at Great Bear Lake in the early s, in two prospectors, Herb Dixon and Johnny Baker, canoed down the Yellowknife River from Great Bear Lake to survey for possible mineral deposits. They found gold samples at Quyta Lake, about 30 km up the Yellowknife River, the following year, Johnny Baker returned as part of a larger crew to develop the previous gold finds and search for more. Gold was found on the east side of Yellowknife Bay in , when government geologists uncovered gold in more favourable geology on the west side of Yellowknife Bay in the fall of , a small staking rush occurred.
From to , one prospector and trapper named Winslow C, Ranney staked in the area between David Lake and Rater Lake with few commercial results. The nearby hill known as Ranney Hill is his namesake and a hiking destination today.tosenemistgar.cf
The acasta Gneisses is a Tonalite Gneiss type of rock. by john madkiff on Prezi
Con Mine entered production on September 5,, the population of Yellowknife quickly grew to 1, by , and by , five gold mines were in production in the Yellowknife region. However, by , gold production had ground to a halt as men were needed for the war effort, an exploration program at the Giant Mine property on the north end of town had suggested a sizable gold deposit in This new find resulted in a massive post-war staking rush to Yellowknife and it also resulted in new discoveries at the Con Mine, greatly extending the life of the mine.
Outcrop — An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.