 tvb now,tvbnow,bttvb! e* A' _, G( d* s
! `% Z0 h" B; A& G) m1 [% r5.39.217.77:8898Asteroid impact craters are among the most interesting geological structures on any planet. Many other
% s$ A- y/ y3 c0 L) E. H# h5 O, vtvb now,tvbnow,bttvbplanets and moons in our solar system, including our own moon, are pock-marked with loads of craters.
' s; x% _5 i5 r# c, W% kTVBNOW 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 because Earth has a protective atmosphere and is geologically active — with plate tectonics and volcanic
. {2 z/ e% H- Peruptions, mostly relatively young oceanic crust, and harsh weathering from wind and water — impact
0 j$ \5 P7 m! Q0 Ctvb now,tvbnow,bttvbstructures don’t last long and can be tough to come by.tvb now,tvbnow,bttvb7 T5 x8 X% |! A1 W) z1 z
6 J: \+ C9 f) x3 F/ ]: p+ }5.39.217.77:8898But on a few old pieces of continent, especially in arid deserts, the marks of asteroids have been preserved.
* c' C; n# N2 Q) T" ntvb now,tvbnow,bttvbOne well-known example is our own Barringer crater, also known as Meteor Crater, in Arizona. The images here
O2 t$ B% T3 @% o6 y' Y, h+ OTVBNOW 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.公仔箱論壇& F6 u, b( d$ b3 E; F
# G9 F4 y' Y! ?. M0 W. g+ q$ k3 [" {tvb now,tvbnow,bttvbAorounga crater, pictured above and below, is one of the best preserved impact craters on Earth, thanks 公仔箱論壇# Q1 M# X! l4 J9 D
in part to its location in the Sahara Desert in Chad. The 10 mile-wide crater is probably around 350 million
' K& f( A9 @" {$ a5.39.217.77:8898years old. The stripes are alternating rock ridges and sand layers, known as yardangs, caused by persistent 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。% F5 L5 J$ F3 T
unidirectional wind. The image above was taken by astronauts in the International Space Station in July. 1 r5 n# { T) v# l7 M8 N: x, {
In the radar image below, taken from the space shuttle in 1994, reveals that Aorounga may be one of two or three craters.
/ x: \) J" j" l6 c- w1 L7 ftvb now,tvbnow,bttvb: b" v5 ~% v, o0 F
 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。+ p) q3 Y9 I. O, h* I
$ E! E1 R/ e' d2 q
 5.39.217.77:8898: i- x$ y' ^3 M9 F8 q5 V6 {
. ?1 M9 y) K, X, K2 E
The Shoemaker crater in Western Australia, formerly known as the Teague crater, was renamed in honor of the planetary
0 G4 a9 s4 q0 @4 N1 a, l; {geologist Eugene Shoemaker for whom the Comet Shoemaker-Levy 9 is also named. The age of the crater unclear, but it 5.39.217.77:8898, x2 K) b! A* v
could be 1.7 billion years old, which makes it the oldest known impact in Australia. The brightly colored splotches are
# m( _0 N6 p2 H) K5.39.217.77:8898seasonal salt-water lakes. This image was taken by the Landsat 7 satellite.
6 V O, Z: K& x" y& v8 E! N: [8 j5.39.217.77:8898
3 d% B( H9 u7 R+ ytvb now,tvbnow,bttvb 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。: B- j9 U5 ?% N4 S! ^' f8 p T3 o
" ^9 [1 r4 r; o6 w0 fTVBNOW 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 Manicouagan Crater in northern Canada is one of the largest impact craters known on Earth. The impact occurred : k$ W* D0 _$ X/ @$ N
around 210 million years ago at the end of the Triassic period and may have caused a mass extinction that killed around 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。4 z+ Z( o' L4 S& ?9 b
60 percent of all species. Though the crater has mostly eroded, Lake Manicouagan outlines what is left of the 43-mile wide 2 C s: U1 a4 [
impact structure. The asteroid that created the crater is thought to have been about three miles wide. Today the lake is a
& P" r z- d, @- l- Y公仔箱論壇reservoir and popular salmon fishing location.
) B6 b" q" O2 j& f8 n/ Jtvb now,tvbnow,bttvb
/ ~: W' g3 x. N 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。+ o+ D9 K9 Q' C8 y4 d: n
. y* y" C. c2 Z0 e2 O3 e0 g公仔箱論壇 ; j5 G# g- K" m' Q0 _
公仔箱論壇4 f N- G% N0 h1 N* i
This crazy looking structure in Western Australia is called the Spider crater, for obvious reasons. Geologists determined it was % E7 ^: Z/ M7 B$ t' S) X6 x
an impact crater when they found shatter cones, telltale cone-shaped, grooved rocks found only around impacts. The crazy + ~- }. M2 `1 z+ ~) u. s
looking legs surrounding the impact are mostly due to erosion of different rock layers. The harder sandstone ridges withstood 5.39.217.77:88985 L* [, c" d0 f, B
the weathering of wind and water better than the softer intervening layers. The crater is somewhere between 600 million
2 b7 \8 M& ?/ }: O公仔箱論壇and 900 million years old and the raised area at its center is around 1,600 feet wide.
2 m- K/ ?6 R0 ^% B0 i7 W$ A$ _! btvb now,tvbnow,bttvb5.39.217.77:8898 x, S l; i N. X
The image above is a false-color image taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on 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。/ Y7 ~8 L2 @6 c' P- W+ @
NASA’s Terra. The true-color image below was captured by Taiwan’s Formost-2 satellite
5 F: _ Z) }- W( J' |
, v1 O, M# c& ?3 D $ B- X- ?, Y* S6 V/ H' Q
$ `. \8 Z; U! R7 G, H1 Z 3 I8 h$ n, R9 \9 R
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。# A$ [7 ~1 T- F! }* Z* O
The Gosses Bluff crater in Australia’s Northern Territory sits between two mountain ranges. The raised circular feature in the 3 ?+ A2 w4 [4 |
center of the structure is around 2.8 miles across, but the original crater rim was probably at the edge of the surrounding , t4 R3 u5 P. E6 C8 O
grayish area. The crater was formed caused by an asteroid impact around 140 million years ago./ E# U- }) e( X Z" ` E% q7 N% R
tvb now,tvbnow,bttvb( { M" O' w( [5 Y, B b( T, Y
: i& N4 h; r, T) s6 utvb now,tvbnow,bttvb
$ ?2 }; A2 `& `6 v ~6 i公仔箱論壇Clearwater Lakes in Quebec, Canada were formed by a pair of asteroid impact craters. The impacts probably occurred
' h, j' \* k$ [4 @5.39.217.77:8898simultaneously around 290 million years ago. The larger crater measures 22 miles across.tvb now,tvbnow,bttvb7 S) N& U% m, b% V1 F% i
% C O& ^9 q5 M# d4 K7 @8 t: C
* R+ E q0 c. n4 i9 d f9 c5.39.217.77:8898
5 V3 }) r4 P. X# ]3 S* S: z; V) 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。The Roter Kamm crater in Namibia is hard to see in visible light, but shows up more clearly with imaging radar. The crater’s 公仔箱論壇! k9 B/ f6 b- }2 W
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
" a0 s) f0 F3 n4 R5.39.217.77:8898 the space shuttle. Irregular surfaces show up brightly and smooth areas are dark. The white splotch at the bottom of the
/ ~, k; c3 k4 }8 u& w5 i. N公仔箱論壇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
1 {, w, D; `: y) qejected during the impact, the red is limestone outcrop and the green areas are mostly vegetation. The impact occurred ( {% Y/ J1 c5 N# d( C7 ~
around 5 million years ago.
7 Q4 i' z; @' F/ |" \5.39.217.77:8898
7 K) c: j3 q4 I. n" V$ l公仔箱論壇
4 }; M0 K. u% Z6 R; b7 NTVBNOW 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。
* R& \& e+ t& |5.39.217.77:8898The Lonar crater in Maharashta, India is around 6,000 feet wide and 500 feet deep and contains a saltwater lake. 8 w4 p- y& \. R6 y5 X$ m0 e3 w
Scientists determined the structure was caused by an asteroid through clues such as the presence of maskelynite,
& e8 H- A0 X3 K$ ~; y) V% u7 O2 i5.39.217.77:8898a glass that is only formed by extremely high-velocity impacts. The impact occurred around 50,000 years ago.
" \; g2 R5 Q# I; T- y3 CThis image was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA’s 5.39.217.77:8898" L# M& \7 d0 U" j
Terra satellite. It is a simulated true-color image
" e2 L! n. X( ?% d% G公仔箱論壇
" V5 z" h: H5 U h" E3 Q. `3 `
% g: Z# u4 u) {6 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。
- E* h) \5 u3 z# tThe Vredefort Dome in South Africa is possibly the oldest and largest clearly visible asteroid impact on Earth. 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。- A5 h1 G/ b0 m0 {! v
The 155-mile crater is approximately 60 miles southwest of Johannesburg and was formed around 2 billion years ago.
( h% O5 ?/ R9 T! ltvb now,tvbnow,bttvbTVBNOW 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。3 M' q7 S8 e; o
 ) g: j/ f1 j0 d7 l$ C3 w7 l
5.39.217.77:8898) m* r# s! |( J" t: k4 e
" w( k" T+ ?; ?, O& z+ a4 \+ N3 I% y
Artist’s rendering of a space object or phenomenon, so we couldn’t resist this beauty. This is one man’s idea of what
" p& z2 s7 ~1 N$ k- d. t- oa 300-mile wide asteroid would look impacting Earth. This event probably would have killed everything on the planet. 1 f5 B% G" j0 k- X( m
Fortunately, NASA says nothing this big is headed our way anytime soon.
|
發表於 2009-12-22 08:55 AM
| 
