 公仔箱論壇1 b# f9 ~4 Z3 H+ f# b; i9 N+ j+ y
& k9 s# a; J. f& Z公仔箱論壇Asteroid impact craters are among the most interesting geological structures on any planet. Many other 9 Y Q' V, M7 _, I
planets and moons in our solar system, including our own moon, are pock-marked with loads of craters.
$ P0 L9 x; X N5 K8 l& \8 uBut because Earth has a protective atmosphere and is geologically active — with plate tectonics and volcanic
; D' O4 Q/ p _5 S公仔箱論壇eruptions, mostly relatively young oceanic crust, and harsh weathering from wind and water — impact 公仔箱論壇$ B2 ?9 R1 ^+ ?' Z4 G% p4 H
structures don’t last long and can be tough to come by.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& o# ^; V! ~' K5 q
& \# F/ c* X# t1 l" L5 ]6 XBut on a few old pieces of continent, especially in arid deserts, the marks of asteroids have been preserved. 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 P! j6 Z% F5 ~0 o
One well-known example is our own Barringer crater, also known as Meteor Crater, in Arizona. The images here
7 y' G. w. D. _: v% k' cshow some of the biggest, oldest and most interesting impact craters on the planet.
, {" M' z) _, j, I4 A% l! t
* I0 R5 F7 W/ M* W) [/ h: z, oAorounga crater, pictured above and below, is one of the best preserved impact craters on Earth, thanks
; B4 S2 A. N! Z5 o6 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。in part to its location in the Sahara Desert in Chad. The 10 mile-wide crater is probably around 350 million
+ ~# o/ S9 B; _+ j% Myears old. The stripes are alternating rock ridges and sand layers, known as yardangs, caused by persistent
0 W, W. }$ Z$ c: a/ U+ U2 g5.39.217.77unidirectional wind. The image above was taken by astronauts in the International Space Station in July.
0 E2 K9 I8 Y8 M3 w+ rTVBNOW 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.公仔箱論壇7 E# a' ^: E1 s. M
8 ?6 E1 b+ z+ z: ]% X0 `. X 5.39.217.775 o$ m; w7 Z6 R7 e8 w8 ?
5.39.217.77- s8 ~. p0 D& v7 W; P1 ]+ C; [0 ^0 ]
 ( A& C0 x' h. | z4 _
; S A/ z: [ 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。The Shoemaker crater in Western Australia, formerly known as the Teague crater, was renamed in honor of the planetary
% Q) N/ ^+ l' @ M' {tvb now,tvbnow,bttvbgeologist Eugene Shoemaker for whom the Comet Shoemaker-Levy 9 is also named. The age of the crater unclear, but it tvb now,tvbnow,bttvb! }9 O* C! |- Q8 _0 F
could be 1.7 billion years old, which makes it the oldest known impact in Australia. The brightly colored splotches are
& {! l# {- T/ p% g6 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。seasonal salt-water lakes. This image was taken by the Landsat 7 satellite.
7 V; L8 K& w A- M9 P, utvb now,tvbnow,bttvb
4 V; J% w$ ^1 l! i6 Z" u5.39.217.77 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。: B/ z2 }; _: h- h
公仔箱論壇) ^5 o. T8 p1 l3 s" p, S0 P
The Manicouagan Crater in northern Canada is one of the largest impact craters known on Earth. The impact occurred ' ^0 r3 @$ t* U# C( y+ K4 I( \
around 210 million years ago at the end of the Triassic period and may have caused a mass extinction that killed around
# z5 U8 {) s8 T! S9 D4 Y- ctvb now,tvbnow,bttvb60 percent of all species. Though the crater has mostly eroded, Lake Manicouagan outlines what is left of the 43-mile wide 4 a5 E3 J z2 ]: n2 \0 B, g
impact structure. The asteroid that created the crater is thought to have been about three miles wide. Today the lake is a
( k9 n) a% k: Q/ R# Zreservoir and popular salmon fishing location.tvb now,tvbnow,bttvb E6 S7 t r) s. r* u
: s. K( S2 ~0 L1 J3 F: k
. _+ L# T% l( W- H6 r- b7 rtvb now,tvbnow,bttvb
& r7 h4 q- E4 B* A0 l; l! p- G$ B, B
6 x) E% O7 a+ _' M# L5 B
% B5 w$ @; d) R V5.39.217.77This crazy looking structure in Western Australia is called the Spider crater, for obvious reasons. Geologists determined it was
7 G$ l% R3 _$ ^ s: P公仔箱論壇an impact crater when they found shatter cones, telltale cone-shaped, grooved rocks found only around impacts. The crazy
! x8 ~6 b4 l9 ?8 d$ Blooking legs surrounding the impact are mostly due to erosion of different rock layers. The harder sandstone ridges withstood
- H$ g0 J0 o# c' T7 X9 d5.39.217.77the weathering of wind and water better than the softer intervening layers. The crater is somewhere between 600 million
5 U: h0 a* D+ u# @. ^1 @6 h' `5.39.217.77and 900 million years old and the raised area at its center is around 1,600 feet wide.
. a7 T8 k% s1 O- a% _tvb now,tvbnow,bttvb
" Z( I, \" N2 o% o0 y7 N8 ~tvb now,tvbnow,bttvbThe image above is a false-color image taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on 5.39.217.77) s2 }' F$ }% J8 n& c# q
NASA’s Terra. The true-color image below was captured by Taiwan’s Formost-2 satellite' n/ B: \' t: x: l
; Z8 Y4 @" [; ^; m3 V/ ]# K5 } tvb now,tvbnow,bttvb6 `1 }% c- u7 `4 s; }3 J( y
, c8 Y8 q2 Q+ r. v7 v$ g% stvb now,tvbnow,bttvb 公仔箱論壇7 | Q; [. H$ s5 h) A& T4 W( K/ Y
* v# Z9 |7 o8 d, F( o* u% b( Rtvb now,tvbnow,bttvbThe Gosses Bluff crater in Australia’s Northern Territory sits between two mountain ranges. The raised circular feature in the
, R' l h& X- \$ D& l公仔箱論壇center of the structure is around 2.8 miles across, but the original crater rim was probably at the edge of the surrounding
' M5 K; V: q# y& v; F& M# b/ agrayish area. The crater was formed caused by an asteroid impact around 140 million years ago.
" _; s, M6 u* _6 l# f7 P
4 \$ v9 x6 d0 a! t8 Otvb now,tvbnow,bttvb r% w) H6 }& p1 | L
8 v. j+ b% M- x1 UTVBNOW 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。Clearwater Lakes in Quebec, Canada were formed by a pair of asteroid impact craters. The impacts probably occurred * C9 a1 G% \4 a! e. k7 c' P, N: E5 a
simultaneously around 290 million years ago. The larger crater measures 22 miles across.
+ r- H- E! p9 E a4 k) e2 C# `4 {! T& G2 C$ E5 F8 U$ y2 B
* D @% o6 P& D! |) Q
3 Y3 C$ q+ f- NThe Roter Kamm crater in Namibia is hard to see in visible light, but shows up more clearly with imaging radar. The crater’s
" N. E- W* v! s4 u+ K( n8 {5.39.217.771.5 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
/ B+ \' n6 Q; f# `, L9 n1 t the space shuttle. Irregular surfaces show up brightly and smooth areas are dark. The white splotch at the bottom of the 4 t$ ~! U0 `: `+ c1 z8 @
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
5 G' o i6 R) w; Btvb now,tvbnow,bttvbejected during the impact, the red is limestone outcrop and the green areas are mostly vegetation. The impact occurred tvb now,tvbnow,bttvb# B0 B$ i" w3 E) S. i* |* U
around 5 million years ago.5.39.217.773 L8 G. u7 _9 T2 r6 _
, N! C0 B8 l( ? O l: L5.39.217.77 公仔箱論壇( F4 k8 e# j; C3 }7 }5 N8 o6 M
' w& V H/ N0 PThe Lonar crater in Maharashta, India is around 6,000 feet wide and 500 feet deep and contains a saltwater lake. ; x% J2 j' N4 r# u) n/ F
Scientists determined the structure was caused by an asteroid through clues such as the presence of maskelynite, tvb now,tvbnow,bttvb: u% P9 s. e" s% n; W
a glass that is only formed by extremely high-velocity impacts. The impact occurred around 50,000 years ago. 5.39.217.77% X8 r- z! ^ {
This image was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA’s
% l: p' o; g% m; i& \. K6 U# cTerra satellite. It is a simulated true-color image
/ u! w2 n7 H( W* f5 e5.39.217.77
* F2 i" Z& k. T" B, I8 Ltvb 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。/ I0 ~! e% L( ?0 z! i) I
j( I! h5 [! mThe Vredefort Dome in South Africa is possibly the oldest and largest clearly visible asteroid impact on Earth.
; z. \9 t/ f! @4 cThe 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。, e. x* a: q" p, s/ q9 J; u
tvb now,tvbnow,bttvb- d% ~3 `' @5 r0 E+ G' a( X
" k: {. N$ a- g( p7 J5.39.217.77! F& o- P, S& S) v
) v, L7 n( v% H" E/ 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。
0 Y2 j% K# T3 V V, P' `: M$ lArtist’s rendering of a space object or phenomenon, so we couldn’t resist this beauty. This is one man’s idea of what
9 K; |- V9 p8 Y0 [/ V$ y4 Ua 300-mile wide asteroid would look impacting Earth. This event probably would have killed everything on the planet.
4 q; N0 C& ?8 ?# xTVBNOW 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。Fortunately, NASA says nothing this big is headed our way anytime soon.
|
發表於 2009-12-22 08:55 AM
| 
