SNOWFLAKE
3 `5 |+ I1 M2 g# @' l Snowflakes form symmetrical (hexagonal) crystals, sometimes matted together if they descend through air warmer than that of the cloud in which they originated. Apparently, no two snow crystals are alike; they differ from each other in size, lacy structure, and surface markings.
. q% O& O3 r! q0 J- c$ f GLEN CANYON DAM! S( r. t% f5 G! {( z' D$ l
on the Colorado River. It is one of the world’s largest concrete dams. The dam, completed in 1963 and
: A9 O H, [% f- S8 x( G$ b5 R. ` dedicated in 1966 after completion of its power-generation facilities, regulates the flow of the upper Colorado and its tributaries and produces hydroelectricity (since 1964). The dam sharply reduced the seasonal flow of the Colorado downstream, dramatically altering the ecology of the river in the Grand Canyon. Changes in water releases have been( e) D& w) f2 p. B5 D7 r. g
experimented with in an attempt to ameliorate the effects of the dam.3 q, n4 [( o- a
MOON% J6 h; ~, q1 ]2 r' E' h$ D
The study of the moon’s surface increased with the invention of the telescope by Galileo in 1610 and culminated in 1969 when the first human actually set foot on the moon’s surface. It has been established that the moon completely lacks both water and atmosphere.
% W( ]! X/ i8 i+ n4 g3 v2 c METHANE
; p" u* N3 { I In 1996, an oceanographic team returned to the site with underwater cameras to probe the seafloor visually. To their surprise, pictures came back showing methane hydrate covering the seafloor like freshly fallen snow. Methane hydrate is a solid that forms when high pressure and low temperatures combine to squeeze water molecules into a crystalline cage around a methane molecule. Cores drilled into the sediments revealed radish-sized lumps of hydrates, which fizzled and evaporated when brought onboard. |
发表于 2012-8-14 23:06:24
