| 单词 | Archean |
| 例句 | Others divide the Precambrian into two eras, the very ancient Archean and the more recent Proterozoic. A Short History of Nearly Everything 2003-05-06T00:00:00Z Explain why ultramafic intrusions, like those of the Muskox Intrusion, are relatively common in Archean rocks, but rare in Phanerozoic rocks. Physical Geology 2015-01-01T00:00:00Z Although there is current evidence that rocks and minerals existed during the Hadean Eon, the Archean has a much more robust rock and fossil record. An Introduction to Geology 2017-01-01T00:00:00Z So Venus's tectonic activity might resemble that on early Earth, during the Archean Eon, between four billion and 2.5 billion years ago, when the heat flow within the planet was higher and the lithosphere thinner. Signs of geological activity found on Venus 2021-06-22T04:00:00Z The fossils date back to earth’s Archean Eon, which lasted from about 4 billion to 2.5 billion years ago. The Oldest Fossils Ever Found Were Discovered in Greenland 2016-08-31T04:00:00Z If any hardy life did manage to succeed during that time, finding its traces in the Archean rock record seems unlikely. Hints of oldest fossil life found in Greenland rocks 2016-08-31T04:00:00Z Geological time has been divided into four eons: Hadean, Archean, Proterozoic, and Phanerozoic, and as shown in Figure 8.3, the first three of these represent almost 90% of Earth’s history. Physical Geology 2015-01-01T00:00:00Z The first solid evidence of modern plate tectonics is found at the end of the Archean, indicating at least some continental lithosphere must have been in place. An Introduction to Geology 2017-01-01T00:00:00Z But Kasting, a world expert in Archean atmospheric models, is confident that the new method is sound. World’s Oldest Space Pebbles Found in Australia 2016-05-11T04:00:00Z Relatively pristine in condition, such outcrops, along with others in South Africa, have long been a popular place to look for traces of life from the Archean eon, which ended 2.5bn years ago. Fossils in Western Australia could hold clues for life on Earth ... and beyond 2013-01-08T14:01:11Z There are few outcrops of Archean rock on Earth, and they tend to be heavily metamorphosed—twisted and deeply altered by heat and pressure. Hints of oldest fossil life found in Greenland rocks 2016-08-31T04:00:00Z Western Canada has a fascinating geological history with rocks ranging in age from the Archean to the Holocene. Physical Geology 2015-01-01T00:00:00Z Archean or Pre-Cambrian rocks, the most ancient in the county, emerge from beneath the newer deposits in three small isolated areas. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 3 "Helmont, Jean" to "Hernosand" 2012-04-14T02:00:23.707Z A better understanding of the properties of Archean Earth's atmosphere may help explain what's known as the "faint young sun" paradox. Primeval Precipitation: What Fossil Imprints of Rain Reveal about Early Earth 2012-03-28T19:45:00.237Z We noted that the difference in Fe isotope composition between Archean seawater and the mean sedimentary pyrite grains is similar to the fractionation we find in our abiotic experiments. [Technical Response] Response to Comment on ?Abiotic Pyrite Formation Produces a Large Fe Isotope Fractionation? 2012-02-02T18:55:40.137Z At one time these rocks were regarded as Archean gneisses of a special type. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 3 "Gordon, Lord George" to "Grasses" 2011-11-13T03:00:13.177Z Hence, though most gneisses are Archean, all gneisses are not necessarily so. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 2 "Gloss" to "Gordon, Charles George" 2011-10-31T02:00:28.703Z The oldest known rocks, those of the Archean era, contain so much igneous matter that many students have assumed that they show that the entire earth was once liquid. Climatic Changes Their Nature and Causes 2011-10-28T02:00:24.840Z The oldest rocks, the gneisses and schists of the Archean period, form nearly the whole of the Central Plateau, and are also exposed in the axes of the folds in Brittany. Encyclopaedia Britannica, 11th Edition, Volume 10, Slice 7 "Fox, George" to "France" 2011-05-15T02:00:07.897Z Given that, similar speculation on rates in the Archean and Palaeoproterozoic are conjectural. [Technical Response] Response to Comment on ?Abiotic Pyrite Formation Produces a Large Fe Isotope Fractionation? 2012-02-02T18:55:40.137Z The Archean period includes the time previous to the deposition of the oldest known sedimentary beds, and its lower limit is as yet undefined. North America 2011-05-05T02:00:20.027Z “We clearly need additional constraints to understand why the Archean Earth remained habitable,” he comments in Nature. Warmth In The Dark Age 2010-04-01T16:26:00Z Here the folded Archean rocks are overlaid by Cambrian and Ordovician beds, which still lie for the most part flat and undisturbed. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 7 "Arundel, Thomas" to "Athens" In the geological history of France there have been two great periods of folding since Archean times. Encyclopaedia Britannica, 11th Edition, Volume 10, Slice 7 "Fox, George" to "France" 2011-05-15T02:00:07.897Z It is to this lowermost gneissic group that the term “Archean” may be conveniently limited. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" Although at the close of the Silurian the continent had greatly increased in area over that of the nucleus at the close of the Archean, it bore but little resemblance to its present form. North America 2011-05-05T02:00:20.027Z With a few exceptions, to be noted later, all the rocks are of pre-Cambrian, perhaps in part of Archean age. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" South and east of the Palaeozoic plateau is an extensive area consisting chiefly of Archean rocks, and including the greater part of Mongolia north of the Tian-shan. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 7 "Arundel, Thomas" to "Athens" This great plain runs north-westward between the border of the Archean protaxis and the line of the Rocky Mountains, including most of Manitoba, the southern part of Saskatchewan and most of Alberta. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" As regards the life of the Archean, or, as some call it, the “Archeozoic” period, we know nothing. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" In the brief description given of the Archean system on a preceding page, it was stated that the rocks composing it are largely metamorphic. North America 2011-05-05T02:00:20.027Z The geological sequence may be summarized as follows:— Archean.—Gneiss, crystalline schists, phyllites, crystalline limestones. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 2 "Chicago, University of" to "Chiton" There is again a floor of folded Archean rocks overlaid by nearly horizontal strata of Lower Palaeozoic age, but these are followed by marine beds belonging to the Carboniferous period. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 7 "Arundel, Thomas" to "Athens" The uneven carving down of the older mountain systems, especially that of the Archean pro taxis, and the disorderly scattering of glacial material provide most of the lake basins so characteristic of Canada. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" Distribution.—It is generally assumed that the Archean rocks underlie all the younger formations over the whole globe, and presumably this is the only system that does so. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" But rocks of practically any age may be altered in the several ways mentioned above, and the resulting gneisses, schists, etc., be indistinguishable from those of the Archean. North America 2011-05-05T02:00:20.027Z Volcanic Rocks.—Amongst the Archean rocks granitic and other intrusions are abundant, but of more modern volcanic activity the remains are comparatively scanty. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 2 "Chicago, University of" to "Chiton" It is the home of the Archean granite, and its basins are of a fathomless dust. Whispering Smith Within the Archean protaxis they are of the most varied shapes, since they represent merely portions of the irregular surface inundated by some morainic dam at the lowest point. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" Britain.—The most important exposure of Archean rocks in Britain is in the north-west of Scotland, where they form the mainland in Sutherland and Ross-shire, and appear also in the outer Hebrides. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" These occur widely throughout North America, and in formations of all ages subsequent to the Archean. North America 2011-05-05T02:00:20.027Z So ancient was the period that these deposits lay next above the primal Archean rocks, and marked, therefore, almost the beginning of accepted geological history. The Book of the National Parks This remarkable and picturesque mass is an isolated "chunk" of the Archean plateau, through which at a later date there has been a volcanic outburst of basalt. Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria" The mountain structures originated in three great orogenic periods, the earliest in the Archean, the second at the end of the Palaeozoic and the third at the end of the Mesozoic. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" The Archean of the Vermilion district of Minnesota comprises the Soudan formation, an altered sedimentary series with banded cherts, jasper and magnetite schists; the iron ores are extensively mined. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" The physical conditions at the earth's surface at the close of the Archean period, as may reasonably be inferred, were not essentially different from what they are now. North America 2011-05-05T02:00:20.027Z Progressively southward they score deeper into the strata of the earth's crust until, as they approach their climax, they break through the bottom of the Paleozoic limestone deep into the heart of the Archean gneiss. The Book of the National Parks The geological structure of that portion of southern Missouri which lies to the westward of the Archean rocks near the Mississippi River is peculiarly suitable for the development of caverns. Archeological Investigations Bureau of American Ethnology, Bulletin 76 The Archean mountain chains, which enclosed the present region of Hudson Bay, were so ancient that they had already been worn down almost to a plain before the early Palaeozoic sediments were laid down. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" The pre-Cambrian cores of the eastern and central Pyrenees, consisting of gneiss, schists and altered limestones, are presumably of Archean age. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" The next system thus far recognised, following the Archean, is the Algonkian, at the close of whose deposition some additions had been made to the Archean or pre-Algonkian land. North America 2011-05-05T02:00:20.027Z This limestone trench is known as the Marble Canyon, the Archean trench as the Granite Gorge. The Book of the National Parks Rocks of Archean age cover wide areas in the interior, in West and East Africa and across the Sahara. The Project Gutenberg Encyclopedia Volume 1 of 28 The Archean protaxis is sometimes spoken of as a plateau, but probably half of it falls below 1000 ft. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 2 "Camorra" to "Cape Colony" It must ever be borne in mind that the presence of a gneissose or schistose complex does not in itself imply the Archean age of such a set of rocks. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" Two important ones, however—namely, Archean and Algonkian—are of American birth. North America 2011-05-05T02:00:20.027Z Yet either is inconsiderable against the total lapse of time even from the Archean's close till now. The Book of the National Parks Sometime during the dim ages preceding the Cambrian, whether in the Archean or in the Algonkian we know not, occurred one of the most important events in the history of the earth. The Elements of Geology Africa contains enormous tracts of crystalline gneisses, granites and schists, and some of these are almost certainly of Archean age; but in the present state of our knowledge it is impossible to speak more exactly. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" It is more than likely that certain occurrences of gneiss and schist, at present regarded as Archean, may prove on fuller examination to be metamorphosed representatives of younger periods. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" The Archean as it remains after this adjustment is termed by Van Hise the Basement Complex. North America 2011-05-05T02:00:20.027Z With the passing of the Archean, the earth had not yet settled into the perfectly balanced sphere which Nature destined it to be. The Book of the National Parks In some regions there rests unconformably on the Archean an immense body of stratified rocks, thousands and in places even scores of thousands of feet thick, known as the ALGONKIAN. The Elements of Geology The definite history of the earth begins with the close of the dim Archean era. The Book of the National Parks North America.—In this continent there is a great development of Archean rocks in Canada. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" This same geological system, the Archean, has a wide development in the continental basin to the north of Lake Superior and about Hudson Bay. North America 2011-05-05T02:00:20.027Z Archeozoic Archean No fossils found, but life inferred from the existence of iron ores and limestones, which are generally formed in the presence of organisms. The Book of the National Parks A theory held by many refers the ultimate source of the iron to the igneous rocks of the Archean. The Elements of Geology The lowest member is a basal conglomerate composed of pebbles derived from the erosion of the dark crumpled schists beneath,—schists which are supposed to be Archean. The Elements of Geology In the Mesaba district of Minnesota the Archean consists of a complex of more or less foliated igneous rocks mostly basic in character. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 "Aram, Eugene" to "Arcueil" Our knowledge is far too meager to warrant an attempt to draw the varying outlines of sea and land during the Archean and Algonkian eras. The Elements of Geology |
| 随便看 |
英语例句辞典收录了117811条英语例句在线翻译词条，基本涵盖了全部常用单词及词组的例句翻译及用法，是英语学习的有利工具。