 公仔箱論壇! E; d0 e2 w4 x5 ]0 Z9 k; {- D; s
# h+ V! w7 T- C) I# ATVBNOW 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。Asteroid impact craters are among the most interesting geological structures on any planet. Many other & `1 s( p( e* T$ R
planets and moons in our solar system, including our own moon, are pock-marked with loads of craters. ; a; A" `# s1 g) h* t& n0 X
But because Earth has a protective atmosphere and is geologically active — with plate tectonics and volcanic
9 ~* {1 p$ _9 v) h& Q, P" V& C+ ^: R公仔箱論壇eruptions, mostly relatively young oceanic crust, and harsh weathering from wind and water — impact
Z) S2 x g- Y% e% A2 q5 |structures don’t last long and can be tough to come by.
/ z" s9 Z* ]3 L0 G3 S4 E- X- C
+ Y% H6 @5 w0 {$ u( _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。But on a few old pieces of continent, especially in arid deserts, the marks of asteroids have been preserved.
, [, C5 w# |+ }One well-known example is our own Barringer crater, also known as Meteor Crater, in Arizona. The images here
5 W' v/ y) c4 z- o5.39.217.77show some of the biggest, oldest and most interesting impact craters on the planet.5.39.217.775 @( l' \' ^ F3 k6 T* f$ t V
tvb now,tvbnow,bttvb' J. |4 s1 `( U8 U. a0 H
Aorounga crater, pictured above and below, is one of the best preserved impact craters on Earth, thanks 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。 V9 h6 v- U, E' {4 M
in part to its location in the Sahara Desert in Chad. The 10 mile-wide crater is probably around 350 million
6 v0 ^- C3 S+ J# Atvb now,tvbnow,bttvbyears old. The stripes are alternating rock ridges and sand layers, known as yardangs, caused by persistent 9 k1 U+ I9 E8 }* w8 H' S# m
unidirectional wind. The image above was taken by astronauts in the International Space Station in July.
8 S6 E# ]" M' w' VTVBNOW 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。In the radar image below, taken from the space shuttle in 1994, reveals that Aorounga may be one of two or three craters.
! ?* i. M+ d: g) _, N& stvb now,tvbnow,bttvb5 z- A! Y9 u) Q/ k
 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。. ^' M7 P5 O9 k5 S# J# ]2 R
0 o( C% \1 m% S9 {; z& h tvb now,tvbnow,bttvb0 s; C- R5 H& H- u& Z8 ?: L7 v
6 I/ p! P v A
The Shoemaker crater in Western Australia, formerly known as the Teague crater, was renamed in honor of the planetary
5 p/ i+ F- T8 Y i+ _+ R: C1 s5.39.217.77geologist Eugene Shoemaker for whom the Comet Shoemaker-Levy 9 is also named. The age of the crater unclear, but it tvb now,tvbnow,bttvb* C9 u& M" [. c, G2 S
could be 1.7 billion years old, which makes it the oldest known impact in Australia. The brightly colored splotches are
$ ?8 W2 ~$ `6 g, Cseasonal salt-water lakes. This image was taken by the Landsat 7 satellite.
5 a8 x2 i: |+ n% w4 A7 R
9 m% a5 \% N3 W L( m8 Q- r2 K* }公仔箱論壇
6 G# ]1 w% b& h% V7 [5.39.217.775.39.217.778 y- I' L p. i T
The Manicouagan Crater in northern Canada is one of the largest impact craters known on Earth. The impact occurred 5.39.217.77, U# d1 w" K" T: V/ L8 u
around 210 million years ago at the end of the Triassic period and may have caused a mass extinction that killed around
" n8 t8 T* P$ f4 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。60 percent of all species. Though the crater has mostly eroded, Lake Manicouagan outlines what is left of the 43-mile wide
1 F: ?3 o2 g# n) I) E5 a5.39.217.77impact structure. The asteroid that created the crater is thought to have been about three miles wide. Today the lake is a 公仔箱論壇' n7 V1 r z. U& r: F& c$ Y7 p
reservoir and popular salmon fishing location.公仔箱論壇4 ?3 l% f, J! a0 b4 n! V
4 f+ E$ K% Y4 p$ w4 u& e9 I P公仔箱論壇 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。) T6 Y }4 S: m. e
$ O* f! e% ~+ e- ltvb now,tvbnow,bttvb 8 _% M% J+ ~" m' A M
5.39.217.77# L& _6 N5 g2 E- s, i
This crazy looking structure in Western Australia is called the Spider crater, for obvious reasons. Geologists determined it was
# S1 ]8 o" S- F+ M# I7 C& J, xan impact crater when they found shatter cones, telltale cone-shaped, grooved rocks found only around impacts. The crazy 9 ?6 h* E3 z8 d9 @3 l+ j( ^
looking legs surrounding the impact are mostly due to erosion of different rock layers. The harder sandstone ridges withstood
, l3 g% e/ H. v0 {9 c) J5 _1 ~公仔箱論壇the weathering of wind and water better than the softer intervening layers. The crater is somewhere between 600 million
& K m& C5 N: U& u6 d2 R' A) q( y; Uand 900 million years old and the raised area at its center is around 1,600 feet wide.
2 A3 f8 Z- a/ @; I) E4 C* F! x
9 o8 z9 w- s) R' F) EThe image above is a false-color image taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on $ G' i- |" u5 u- t" D
NASA’s Terra. The true-color image below was captured by Taiwan’s Formost-2 satellite O8 u& ^- j. w* K
公仔箱論壇# U1 B# p1 T6 y, [
: k! h3 d5 u6 Y0 ?tvb now,tvbnow,bttvb5.39.217.771 V% T$ I% `; j% u
 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。& J* S3 p/ D9 f0 L4 r3 Y
tvb now,tvbnow,bttvb9 W0 E; P2 S1 l3 t& Y
The Gosses Bluff crater in Australia’s Northern Territory sits between two mountain ranges. The raised circular feature in the
" W# |+ [# V" ~ e6 z& ^1 _center of the structure is around 2.8 miles across, but the original crater rim was probably at the edge of the surrounding
7 }# q7 Z; K* {/ Z! q% F公仔箱論壇grayish area. The crater was formed caused by an asteroid impact around 140 million years ago.8 l5 a* W3 w/ z5 O
8 M. f2 }1 |6 ?& z4 n+ @0 d1 p7 `
" u! E; G' A4 i, y/ B- z4 q" |$ r9 A
Clearwater Lakes in Quebec, Canada were formed by a pair of asteroid impact craters. The impacts probably occurred
. n: t/ z7 y' ~% q' F7 atvb now,tvbnow,bttvbsimultaneously around 290 million years ago. The larger crater measures 22 miles across.. I. n3 `+ Y, V8 F1 ]. i6 ^
tvb now,tvbnow,bttvb6 n: x. c2 M, A/ x. ~& t! D. e! \
 tvb now,tvbnow,bttvb( n5 R) B) U" ^7 R6 V# o/ o. A* _
( y" Y8 A2 ^0 K. f0 Y; 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 Roter Kamm crater in Namibia is hard to see in visible light, but shows up more clearly with imaging radar. The crater’s 5.39.217.770 S: c" w8 j2 k1 k g/ @8 z
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
6 G" [* d: Y' `: \& f, @9 p. Gtvb now,tvbnow,bttvb the space shuttle. Irregular surfaces show up brightly and smooth areas are dark. The white splotch at the bottom of the
: Q/ K4 a Z; B- G) `7 E1 t) xphoto is a rocky hill, the darkest areas are wind-blown sand dunes, the blue around the crater’s rim may be material that was
; F1 g3 n( u1 k# i* p# J D3 pTVBNOW 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
' N1 K8 r$ Q2 M( e: {around 5 million years ago.5.39.217.770 {; e2 p4 o0 k( [9 l
' ]! Z, T7 I. d5 t5.39.217.77 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。" Z# R2 X& v6 w* 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。9 a$ @5 y7 h N0 W
The Lonar crater in Maharashta, India is around 6,000 feet wide and 500 feet deep and contains a saltwater lake.
/ D1 s( r& S3 L' K# HScientists determined the structure was caused by an asteroid through clues such as the presence of maskelynite, 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。 J, y9 U5 N. g9 }: r! \5 \& {
a glass that is only formed by extremely high-velocity impacts. The impact occurred around 50,000 years ago.
+ v; }; }( j/ U/ B) n; xThis image was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA’s 公仔箱論壇* o% ]; V9 e' Y* f" {% { p3 ?
Terra satellite. It is a simulated true-color image* R- z7 {: p8 m. Q7 R8 |
tvb now,tvbnow,bttvb! }9 h+ E2 [1 b/ w# v4 k* p
 公仔箱論壇7 y& {4 i$ h t( k5 Y8 v9 }+ I
7 l7 V9 s+ O( s$ T
The Vredefort Dome in South Africa is possibly the oldest and largest clearly visible asteroid impact on Earth.
" O8 A& p* @! n1 L8 h公仔箱論壇The 155-mile crater is approximately 60 miles southwest of Johannesburg and was formed around 2 billion years ago.5.39.217.77: }& x1 h8 j4 U I: i
, n/ ]; ~+ P f. D0 X5.39.217.77 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。! H3 n) C/ q% w& Z: t
& U P8 h( Y: ~( G5.39.217.77 9 {8 {9 w: a/ H3 m# B3 S/ {+ L
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。& D; ?6 e+ R% U- p- Z; l! N
Artist’s rendering of a space object or phenomenon, so we couldn’t resist this beauty. This is one man’s idea of what
! K) J9 Q, a h& |a 300-mile wide asteroid would look impacting Earth. This event probably would have killed everything on the planet.
# s! V2 W5 u9 K- s& Z, X: t5.39.217.77Fortunately, NASA says nothing this big is headed our way anytime soon.
|
發表於 2009-12-22 08:55 AM
| 
