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4 i# }& X& V7 d0 |8 o- a" b( wtvb now,tvbnow,bttvbAsteroid impact craters are among the most interesting geological structures on any planet. Many other ( v. z" G% W; }, h
planets and moons in our solar system, including our own moon, are pock-marked with loads of craters.
( x& i3 P8 D; N5 @# O3 u' h9 {' GBut because Earth has a protective atmosphere and is geologically active — with plate tectonics and volcanic
" g8 S A5 N4 y5 t0 [2 B公仔箱論壇eruptions, mostly relatively young oceanic crust, and harsh weathering from wind and water — impact
( d# a4 |' t7 P5.39.217.77structures don’t last long and can be tough to come by.
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( |1 |4 l* R1 e% Q) \& {) itvb now,tvbnow,bttvbBut on a few old pieces of continent, especially in arid deserts, the marks of asteroids have been preserved. ( W N. r. r* d3 U/ C" E! S
One well-known example is our own Barringer crater, also known as Meteor Crater, in Arizona. The images here
! V. x6 ]' n9 v5 m; {' [. V& X zTVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。show some of the biggest, oldest and most interesting impact craters on the planet.
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" A6 u1 }, F, ctvb now,tvbnow,bttvbAorounga crater, pictured above and below, is one of the best preserved impact craters on Earth, thanks
# r. ]* U; w5 K% Y* ~公仔箱論壇in part to its location in the Sahara Desert in Chad. The 10 mile-wide crater is probably around 350 million 5.39.217.77# _# O4 c c/ _) k) I" K/ Y
years old. The stripes are alternating rock ridges and sand layers, known as yardangs, caused by persistent 7 v' D. q- s2 s! G+ O
unidirectional wind. The image above was taken by astronauts in the International Space Station in July.
7 ?' H: h- c( a% p+ e% i- aIn the radar image below, taken from the space shuttle in 1994, reveals that Aorounga may be one of two or three craters.
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The Shoemaker crater in Western Australia, formerly known as the Teague crater, was renamed in honor of the planetary
5 W: R8 Q0 n" jTVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。geologist Eugene Shoemaker for whom the Comet Shoemaker-Levy 9 is also named. The age of the crater unclear, but it TVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。" H4 ^0 \- m8 ~/ G
could be 1.7 billion years old, which makes it the oldest known impact in Australia. The brightly colored splotches are 公仔箱論壇& s+ l% D2 ]( h9 m3 S8 z; g3 w, `
seasonal salt-water lakes. This image was taken by the Landsat 7 satellite.5.39.217.77# F1 q! ~! {9 P
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# B8 n! R6 m) c- H) _9 CThe Manicouagan Crater in northern Canada is one of the largest impact craters known on Earth. The impact occurred
1 D5 Y( e& M* w, T3 S6 b5 ~公仔箱論壇around 210 million years ago at the end of the Triassic period and may have caused a mass extinction that killed around
9 \ O5 S k% A6 O& D9 |60 percent of all species. Though the crater has mostly eroded, Lake Manicouagan outlines what is left of the 43-mile wide
& T; \$ b v8 [: m: g# _2 E: x- BTVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。impact structure. The asteroid that created the crater is thought to have been about three miles wide. Today the lake is a TVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。/ g* t: \& b2 a
reservoir and popular salmon fishing location.
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This crazy looking structure in Western Australia is called the Spider crater, for obvious reasons. Geologists determined it was
' {) D7 q! d6 K# d1 a @ y' f+ Wan impact crater when they found shatter cones, telltale cone-shaped, grooved rocks found only around impacts. The crazy
' m/ ?' I) m) q/ Ftvb now,tvbnow,bttvblooking legs surrounding the impact are mostly due to erosion of different rock layers. The harder sandstone ridges withstood
1 E( C! o- s6 z" x# V! cthe weathering of wind and water better than the softer intervening layers. The crater is somewhere between 600 million
$ @, Y5 i6 t$ O8 S) X: Y" {5.39.217.77and 900 million years old and the raised area at its center is around 1,600 feet wide.
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5 R# M R6 @) u- I4 v! eThe image above is a false-color image taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on tvb now,tvbnow,bttvb- {5 U& e% q1 x+ y, `# f3 l
NASA’s Terra. The true-color image below was captured by Taiwan’s Formost-2 satellite公仔箱論壇% R+ N/ L- }! `! e% L1 I& G$ G
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6 d+ S: {5 H% w: z公仔箱論壇The Gosses Bluff crater in Australia’s Northern Territory sits between two mountain ranges. The raised circular feature in the 公仔箱論壇3 y" S$ ]" |9 }# ?/ _ e0 Y* F+ f
center of the structure is around 2.8 miles across, but the original crater rim was probably at the edge of the surrounding
$ }9 a$ {4 b; f8 [% k. H' U( ^% u8 ggrayish area. The crater was formed caused by an asteroid impact around 140 million years ago.tvb now,tvbnow,bttvb& P N8 j& p, ? v! A' S. U) I' X+ v f
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Clearwater Lakes in Quebec, Canada were formed by a pair of asteroid impact craters. The impacts probably occurred
/ G& `" N: L# |) u1 z; Zsimultaneously around 290 million years ago. The larger crater measures 22 miles across.3 {9 L+ z a% o A: m) a# y9 V$ Y# O
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The Roter Kamm crater in Namibia is hard to see in visible light, but shows up more clearly with imaging radar. The crater’s 5.39.217.77$ K9 @. e9 E; L- n0 T: s1 p' p2 q
1.5 mile-wide rim stands out as a bright ring in the lower left of the image, which was taken by a radar instrument on board
2 \1 S$ t3 M) [, X2 K1 {& C5.39.217.77 the space shuttle. Irregular surfaces show up brightly and smooth areas are dark. The white splotch at the bottom of the
m: L+ R( Q. m( g! Y- [tvb now,tvbnow,bttvbphoto is a rocky hill, the darkest areas are wind-blown sand dunes, the blue around the crater’s rim may be material that was / a+ n( K! J4 a+ `4 l/ _! Z$ g
ejected during the impact, the red is limestone outcrop and the green areas are mostly vegetation. The impact occurred $ z5 K" ]7 {$ J' B
around 5 million years ago.
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The Lonar crater in Maharashta, India is around 6,000 feet wide and 500 feet deep and contains a saltwater lake. 5.39.217.77( q S* z* F: u) u
Scientists determined the structure was caused by an asteroid through clues such as the presence of maskelynite,
4 ~+ w8 n) {) r9 T4 D4 O5.39.217.77a glass that is only formed by extremely high-velocity impacts. The impact occurred around 50,000 years ago.
+ W- [" v. j) x0 A3 _6 t& A" s$ wThis image was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA’s
7 _1 [6 a! @# [* r6 s8 h3 otvb now,tvbnow,bttvbTerra satellite. It is a simulated true-color image公仔箱論壇2 f1 K; b; p$ v8 `7 Y
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The Vredefort Dome in South Africa is possibly the oldest and largest clearly visible asteroid impact on Earth. ) v8 M1 |1 {- o$ k2 t. z
The 155-mile crater is approximately 60 miles southwest of Johannesburg and was formed around 2 billion years ago.
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Artist’s rendering of a space object or phenomenon, so we couldn’t resist this beauty. This is one man’s idea of what
' v1 ^: V/ }8 B7 }6 H% f. T9 ga 300-mile wide asteroid would look impacting Earth. This event probably would have killed everything on the planet. 公仔箱論壇' B! U2 C a* j0 w$ f* Y
Fortunately, NASA says nothing this big is headed our way anytime soon.
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發表於 2009-12-22 08:55 AM
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