Plate tectonics is a theory of geology developed to explain the phenomenon of continental drift, and is currently the theory accepted by the vast majority of scientists working in this area. In the theory of plate tectonics the outermost part of the Earth's interior is made up of two layers, the outer lithosphere and the inner asthenosphere.
The lithosphere essentially "floats" on the asthenosphere and is broken-up into ten major plates. These plates (and the more numerous minor plates) move in relation to one another at one of three types of plate boundaries: convergent (two plates push against one another), divergent (two plates move away from each other), and transform (two plates slide past one another).
Plate tectonic theory arose out of two separate geological observations: continental drift, noticed in the early 20th century, and seafloor spreading, noticed in the 1960s. The theory itself was developed during the late 1960s and has since almost universally been accepted by scientists and has revolutionized the Earth sciences (akin to the development of the periodic table for chemistry, the discovery of the genetic code for genetics, or evolution in biology).
A geyser is a type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air. The name geyser comes from Geysir, the name of an erupting spring at Haukadalur, Iceland; that name, in turn, comes from the Icelandic verb gjósa, "to gush".
The formation of geysers requires a favourable hydrogeology which exists in only a few places on Earth, and so they are fairly rare phenomena. About 1000 exist worldwide, with about half of these in Yellowstone National Park, USA (Glennon, J.A. 2005). Geyser eruptive activity may change or cease due to ongoing mineral deposition within the geyser plumbing, exchange of functions with nearby hot springs, earthquake influences, and human intervention (Bryan, T.S. 1995).
Erupting fountains of liquefied nitrogen have been observed on Neptune's moon Triton. These phenomena are also often referred to as geysers. On Triton, the geysers appear to be driven by solar heating instead of geothermal energy. The nitrogen, liquefied by a kind of greenhouse effect, may erupt to heights of 8 km.
An ice age is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ("glaciation"). Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ice age is used to refer to colder periods with extensive ice sheets over the North American and Eurasian continents: in this sense, the last ice age ended about 10,000 years ago. This article will use the term ice age in the former, glaciological, sense; and use the term 'glacial periods' for colder periods during ice ages and 'interglacial' for the warmer periods.
During the last few million years, there have been many glacial periods, occurring initially at 40,000-year frequency but more recently at 100,000-year frequencies. There have been four major ice ages in the further past.
The rest of 2006
Did you know
- ...that the word "geology" was first used by Richard de Bury and it was used to distinguish between earthly and theological jurisprudence? Its current use was begun by Jean-André Deluc in the year 1778. More...
- ...that the continent Atlantica formed two billion years ago and is now the continents Africa and South America? More...
- ...that andesitic magma in island arc regions (i.e. active oceanic margins) comes from wet melting of mantle wedge peridotite? More...
- ...that the first stromatolites appeared in the Mesoarchean era of the Archean eon? More...
- ...that the small rounded bodies about the size of rice that commonly occur in vitreous igneous rocks such as obsidian, pitchstone and rhyolite are called "spherulites", and when examined with a lens they prove to have a fibrous structure? More...
- ...that Canadian geologist and paleontologist Alice Wilson became the first female Fellow of the Royal Society of Canada in 1937? More...
- ...that Louis Agassiz was the first to scientifically propose that the Earth had been subject to a past ice age. More...
- ...that Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), hornblende, and/or pyroxene. More...
- ...that Black smokers are a type of hydrothermal vent found on the ocean floor. More...
- ...that the troposphere is the lowermost portion of Earth's atmosphere and the one in which most weather phenomena occur. More...
- ...that Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. More...
- ...that Io is the most volcanically active body in our solar system, due to the tides exerted upon the satellite by Jupiter. More...
November 25, 2005: Researchers in Antarctica have found that icebergs "sing". Unlike singing sand dunes, iceberg "songs" are not audible to humans. It is believed that the iceberg sounds are due to water flowing through crevasses inside it. The flow of water is caused when an iceberg hits the sea floor, slowing down; the water inside continues moving, building up water pressure, getting the iceberg walls to vibrate. This would produce regularly spaced tremors, resulting in the oscillating "songs".
November 24, 2005: A record ice-core reveals information of the Earth's atmosphere, showing correlations between greenhouse gases and temperature changes. This ice-core, taken by the European Project for Ice Coring in Antarctica is 3270 metres long.
January 15, 2006: The Chesapeake Bay Impact Crater Deep Drilling Project was completed successfully. A 1.77km (1.1 miles) core was taken within the crater, being one of the most complete cores ever taken from an impact structure. Article on ScienceDaily
January 4, 2006: "Global warming millions of years ago put seas in a spin: The circulation of the deep oceans reversed abruptly some 55 million years ago, according to a study of fossilized sea creatures. This rings alarm bells about today's climate change, because the reversal coincided with a period of global warming driven by greenhouse gases." Article on Nature News