Geological history of Earth Geologic time represented in a diagram called a geological clock, showing the relative lengths of the eons of Earth's history and noting major events The geological history of Earth follows the major events in Earth's past based on the geologic time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System. As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. The present pattern of ice ages began about 40 million years ago, then intensified at the end of the Pliocene. Precambrian[edit] The Precambrian includes approximately 90% of geologic time. Hadean Eon[edit] Archean Eon[edit] By 3.5 billion years ago, the Earth's magnetic field was established. Proterozoic Eon[edit]
KIC 12557548 History of detection[edit] The existence of the planet was first evidenced in data collected by the Kepler spacecraft. However, the light curve of the star, a graph of its stellar flux versus time, showed that while there were regular drops in stellar flux approximately every 15 hours, the amount of light being blocked covered a wide range, from 0.2% to 1.3% of the starlight being blocked.[2] Rappaport et al. (2012) proposed various possible phenomena which may have caused the anomalies in the light curve, including two planets orbiting each other,[6] and an eclipsing binary orbiting the star in a larger triple-star system.[2] However, the authors found the hypothetical binary planet system to be unstable[2] and the latter scenario to be poorly supported by the data collected by Kepler.[2] Planetary system[edit] References[edit] ^ Jump up to: a b c d e f "Basic data: 2MASS J19235189+5130170 -- Infra-Red source". Brogi, M.; Keller, C. Notes[edit] External links[edit]
untitled The Autobiography of Benjamin Franklin Chapter One The Author's Reasons for undertaking the present Work---A Dissertation upon Vanity---Some Account of his Ancestors---He discovers that he is the youngest Son of the youngest Son for five Generations---Young Franklin is at first destined for the Church---His Father soon after takes him from School and emplys him as an Assistant in making Candles, Etc.---He is desirous of being a Sailor---Some Account of his youthful Frolicks--- Becomes greatly attached to Books---Is bound Apprentice to a Printer---Begins to study Composition---Adopts a vegetable Regimen---And is extremely fond of Disputation. TWYFORD, at the Bishop of St. Dear son: I have ever had pleasure in obtaining any little anecdotes of my ancestors. And now I speak of thanking God, I desire with all humility to acknowledge that I owe the mentioned happiness of my past life to His kind providence, which lead me to the means I used and gave them success. John was bred a dyer, I believe of woolens. End of Chapter One.
Geologic time scale Online exhibits Geologic time scale Take a journey back through the history of the Earth — jump to a specific time period using the time scale below and examine ancient life, climates, and geography. You might wish to start in the Cenozoic Era (65.5 million years ago to the present) and work back through time, or start with Hadean time (4.6 to 4 billion years ago)* and journey forward to the present day — it's your choice. Ways to begin your exploration: Use the links in the "time machine" below and explore a specific period that interests you.Read more about the geologic time scale, its origins and its time divisions.Find out more about plate tectonics, an important geological concept in any time period!
Future of the Earth Conjectured illustration of the scorched Earth after the Sun has entered the red giant phase, 7 billion years from now.[1] During the next four billion years, the luminosity of the Sun will steadily increase, resulting in a rise in the solar radiation reaching the Earth. This will cause a higher rate of weathering of silicate minerals, which will cause a decrease in the level of carbon dioxide in the atmosphere. In about 600 million years, the level of CO 2 will fall below the level needed to sustain C3 carbon fixation photosynthesis used by trees. Some plants use the C4 carbon fixation method, allowing them to persist at CO 2 concentrations as low as 10 parts per million. In about 1.1 billion years, the solar luminosity will be 10% higher than at present. Human influence[edit] There are multiple scenarios for known risks that can have a global impact on the planet. Should the human race become extinct, then the various features assembled by humanity will begin to decay. Glaciation[edit]
untitled Axial Age Pivotal age characterizing history and philosophy from the 8th to 3rd centuries BCE Axial Age (also Axis Age,[1] from German: Achsenzeit) is a term coined by German philosopher Karl Jaspers. It refers to broad changes in religious and philosophical thought that occurred in a variety of locations from about the 8th to the 3rd century BC. According to Jaspers, during this period, universalizing modes of thought appeared in Persia, India, China, the Levant, and the Greco-Roman world, in a striking parallel development, without any obvious admixture between these disparate cultures. Origin of the idea of Axial Age[edit] Jaspers introduced the concept of an Axial Age in his book Vom Ursprung und Ziel der Geschichte (The Origin and Goal of History),[7] published in 1949. Jaspers identified a number of key thinkers as having had a profound influence on future philosophies and religions, and identified characteristics common to each area from which those thinkers emerged. Characteristics[edit]
Prehistory Prehistory (meaning "before history", or "before knowledge acquired by investigation", from the Latin word for "before," præ, and historia) is the span of time before recorded history or the invention of writing systems. Prehistory refers to the period of human existence before the availability of those written records with which recorded history begins.[1] More broadly, it can refer to all the time preceding human existence and the invention of writing. The notion of "prehistory" began to surface during the Enlightenment in the work of antiquarians who used the word 'primitive' to describe societies that existed before written records.[2] The first use of the word prehistory in English, however, occurred in the Foreign Quarterly Review in 1836.[3] The occurrence of written materials (and so the beginning of local "historic times") varies generally to cultures classified within either the late Bronze Age or within the Iron Age. Definition[edit] Stone Age[edit] Paleolithic[edit] uninhabited
Holocene extinction The dodo, a flightless bird of Mauritius, became extinct during the mid-late seventeenth century after humans destroyed the forests where the birds made their homes and introduced mammals that ate their eggs. The Holocene extinction includes the disappearance of large mammals known as megafauna, starting between 9,000 and 13,000 years ago, the end of the last Ice Age. This may have been due to the extinction of the mammoth that had maintained grasslands that became birch forests without the mammoths.[3] The new forest and the resulting forest fires may have induced climate change.[3] Such disappearances might be the result of the proliferation of modern humans which led to climate change. These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event. The Holocene extinction continues into the 21st century. Prehistoric extinctions[edit] North and South America[edit] New Zealand[edit] Pacific, including Hawaii[edit]
untitled Geology Entrance You might wish to start in the Cenozoic Era (65 million years ago to the present) and work back through time, or start with Hadean time (4.5 to 3.8 billion years ago) and journey forward to the present day. No matter "when" you start, don't forget to stop along the way to learn about the stratigraphy, ancient life, fossil localities, and tectonics of the various time periods. Here are three links that can help to speed your journey: 1) Get helpful hints on navigating the Geology Wing. 2) Read about the history of the geologic time scale, and find out more about how it is organized. 3) Jump to a specific time period using the UCMP Geological Time Machine. Last but not least, don't forget to visit our exhibit on Plate tectonics, an important geological concept in any time period!
Ross 248 This star has about 12% of the Sun's mass and 16% of the Sun's radius, but only 0.2% of the Sun's luminosity. It has a stellar classification of M6 V,[3] which indicates it is a type of main sequence star known as a red dwarf. This is a flare star that occasionally increases in luminosity.[13] With high probability there appears to be a long-term cycle of variability with a period of 4.2 years. Long term observations of this star by the Sproul Observatory show no astrometric perturbations by an unseen companion.[15] The proper motion of this star was examined for a brown dwarf or stellar companion orbiting at a wide separation (between 100–1400 AU) but none was found.[16] A search for a faint companion using the Hubble Space Telescope Wide Field Planetary Camera revealed nothing,[7] nor did a search with near-infrared speckle interferometry.[17] However, none of these searches rule out a companion that is smaller than the detection minima. Field star[edit] See also[edit] References[edit]
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