3 i/ [2 n$ u; U4 p. y8 C; S4 hTVBNOW 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。- w( {3 R$ n# h5 `! c, ~# F, f; [
Asteroid impact craters are among the most interesting geological structures on any planet. Many other
# p" r2 X$ m9 z: u) N& CTVBNOW 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。planets and moons in our solar system, including our own moon, are pock-marked with loads of craters. 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。! c6 F, k+ P9 [8 J- f
But because Earth has a protective atmosphere and is geologically active — with plate tectonics and volcanic
' L( G$ r8 {9 R$ N) leruptions, mostly relatively young oceanic crust, and harsh weathering from wind and water — impact
9 [8 I1 Y3 f- g7 R0 m& Owww3.tvboxnow.comstructures don’t last long and can be tough to come by.
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But on a few old pieces of continent, especially in arid deserts, the marks of asteroids have been preserved. 8 L, p- G3 `6 W% S/ L" A/ R$ m; ~
One well-known example is our own Barringer crater, also known as Meteor Crater, in Arizona. The images here
4 n. F$ ^: n8 b5 g3 Y0 j% Otvb now,tvbnow,bttvbshow some of the biggest, oldest and most interesting impact craters on the planet.
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- L8 A0 U# ?0 L' H  v5 ]tvb now,tvbnow,bttvbAorounga crater, pictured above and below, is one of the best preserved impact craters on Earth, thanks www3.tvboxnow.com  n: Y  e7 u! l. x
in part to its location in the Sahara Desert in Chad. The 10 mile-wide crater is probably around 350 million 公仔箱論壇- u2 l9 f( a! b0 X; G# t) @: i+ X
years old. The stripes are alternating rock ridges and sand layers, known as yardangs, caused by persistent # g9 q( D  J! v0 K
unidirectional wind. The image above was taken by astronauts in the International Space Station in July. tvb now,tvbnow,bttvb- y8 x* M9 e3 E
In the radar image below, taken from the space shuttle in 1994, reveals that Aorounga may be one of two or three craters.tvb now,tvbnow,bttvb3 ?# n- q$ {4 ^' `# k3 B4 U& `4 _
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# b5 E7 \" d0 e: o+ mThe Shoemaker crater in Western Australia, formerly known as the Teague crater, was renamed in honor of the planetary + ~- ]. _1 ]/ h- I! m, f
geologist Eugene Shoemaker for whom the Comet Shoemaker-Levy 9 is also named. The age of the crater unclear, but it
! E9 R% g5 f. [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. Q/ x: l7 J. e: G7 @" S$ g
seasonal salt-water lakes. This image was taken by the Landsat 7 satellite.! D, C  s+ e% W2 Z' f

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& l( ~4 I( ?* [The Manicouagan Crater in northern Canada is one of the largest impact craters known on Earth. The impact occurred tvb now,tvbnow,bttvb9 W& N, v: P, P) N. j
around 210 million years ago at the end of the Triassic period and may have caused a mass extinction that killed around
1 M2 v2 }1 W4 B1 r3 A60 percent of all species. Though the crater has mostly eroded, Lake Manicouagan outlines what is left of the 43-mile wide
6 y/ A8 V  m' u* Pimpact 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。+ f- F2 y; |" w# q1 e- U( v
reservoir and popular salmon fishing location.
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* l6 o3 p4 e( F" f  x/ \' M# ~www3.tvboxnow.comThis crazy looking structure in Western Australia is called the Spider crater, for obvious reasons. Geologists determined it was 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。7 Z% R; k  v3 G$ K6 g
an impact crater when they found shatter cones, telltale cone-shaped, grooved rocks found only around impacts. The crazy
, E# |9 t3 M6 I$ o( Qlooking legs surrounding the impact are mostly due to erosion of different rock layers. The harder sandstone ridges withstood www3.tvboxnow.com/ F" w9 Q8 o0 t3 _# O3 X, H
the weathering of wind and water better than the softer intervening layers. The crater is somewhere between 600 million 公仔箱論壇2 ]) |' V- Z/ I
and 900 million years old and the raised area at its center is around 1,600 feet wide., G- n) g2 b0 K$ x/ R* B$ V

9 R3 A, x! d* g& }1 G4 {/ t$ STVBNOW 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。The image above is a false-color image taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on
! j6 [9 j/ N6 D, `$ ptvb now,tvbnow,bttvbNASA’s Terra. The true-color image below was captured by Taiwan’s Formost-2 satelliteTVBNOW 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。6 F# B# J3 Y1 G2 e2 [
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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。* }' E9 j+ x; U( }9 A% Q  m1 w

% K3 i9 Y+ ~9 |tvb now,tvbnow,bttvbThe Gosses Bluff crater in Australia’s Northern Territory sits between two mountain ranges. The raised circular feature in the www3.tvboxnow.com$ y4 b. D7 r  l1 f( w' ~+ b
center of the structure is around 2.8 miles across, but the original crater rim was probably at the edge of the surrounding www3.tvboxnow.com2 n, [$ n) P5 K" i
grayish area. The crater was formed caused by an asteroid impact around 140 million years ago.
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Clearwater Lakes in Quebec, Canada were formed by a pair of asteroid impact craters. The impacts probably occurred www3.tvboxnow.com1 o6 U# l* |0 Z2 U* w' J
simultaneously around 290 million years ago. The larger crater measures 22 miles across.: G  {% n7 v; ?" e

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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 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。/ Y: n" J9 P* ]$ x6 f7 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 board1 T" e! S# `0 j9 e
the space shuttle. Irregular surfaces show up brightly and smooth areas are dark. The white splotch at the bottom of the tvb now,tvbnow,bttvb6 M( A- v- V2 d' ]
photo is a rocky hill, the darkest areas are wind-blown sand dunes, the blue around the crater’s rim may be material that was
! s9 Z% P8 d! k+ k  r) A$ X8 iTVBNOW 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。ejected during the impact, the red is limestone outcrop and the green areas are mostly vegetation. The impact occurred % I$ R0 h* c$ m4 F
around 5 million years ago.
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" P8 U; T% l, d6 I) W" }: Ctvb now,tvbnow,bttvbThe Lonar crater in Maharashta, India is around 6,000 feet wide and 500 feet deep and contains a saltwater lake. 7 N" \+ a& b6 i( i8 e5 Z. v' A* ^
Scientists determined the structure was caused by an asteroid through clues such as the presence of maskelynite,
0 m3 Z# p* }2 x% k6 z8 j$ P+ Pa glass that is only formed by extremely high-velocity impacts. The impact occurred around 50,000 years ago.
- c6 ]; i3 i7 t+ Htvb now,tvbnow,bttvbThis image was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA’s
% O- X  p% r) ~) q- ?5 ITerra satellite. It is a simulated true-color image公仔箱論壇6 E* y3 u2 p3 O

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The Vredefort Dome in South Africa is possibly the oldest and largest clearly visible asteroid impact on Earth.
+ {" h" b/ |0 D: Z# }The 155-mile crater is approximately 60 miles southwest of Johannesburg and was formed around 2 billion years ago.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。& @2 R3 l! f( `/ \3 s" Z

- U" ^6 P3 X6 R. o0 n9 wTVBNOW 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。公仔箱論壇5 K. d, `1 M. h- C8 K- c

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  f- u5 J  P2 z) k: ^: {tvb now,tvbnow,bttvbArtist’s rendering of a space object or phenomenon, so we couldn’t resist this beauty. This is one man’s idea of what
3 f" H% W7 D$ C8 o2 m2 STVBNOW 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。a 300-mile wide asteroid would look impacting Earth. This event probably would have killed everything on the planet. ! z( k3 p; N% @: E9 a/ q
Fortunately, NASA says nothing this big is headed our way anytime soon.