科學新聞情報間

最近更新日期:2010-07-03 | 30 次瀏覽 |


以簡短的文字及圖片,介紹最新的科學報導。



文章列表

….回到前面



火山島弧的位置?

最近更新日期:2010-10-17 | 167 次瀏覽 |

火山島弧的形成,源自於隱沒板塊脫水,造成地函岩石產生部分熔融所需溫度(含水飽和固熔線)降低,所形成的岩漿所造成。但是火山島弧的分佈位置並非由此過程所控制,而是由地函不含水岩石熔融所需溫度(不含水固熔線)的分佈所控制。

圖中橘色系區域為含水飽和固熔線所包圍,其內可產生部分熔融的岩漿。黑色網格則由不含水固熔線所包圍,為岩漿產生上湧的位置。

原始論文:England, P.C. & Richard F. Katz, Melting above the anhydrous solidus controls the location of volcanic arcs, Nature, V467, P700–703 (2010) .


水、地震、橄欖石、隱沒作用

最近更新日期:2010-10-17 | 122 次瀏覽 |

根據最新的實驗岩石學研究結果顯示,橄欖石在高壓下的各種型態,可以在隱沒作用的過程中,將結晶水帶往地函深處。在一系列含水礦物脫水的過程中,會導致不同深度的地震發生(如圖)。在深度250公里的範圍內,幾乎可以一一地對應。但在深度400公里以下,就不再能夠判別出礦物脫水所導致的地震。顯示隱沒作用可能無法將水帶到地函過渡帶以下的深度。

原始論文:Green II, H.W. et al., Seismic evidence of negligible water carried below 400-km depth in subducting lithosphere, Nature, V467, P828–831 (2010).


星系冷流?!

最近更新日期:2010-10-17 | 46 次瀏覽 |

一般星系內部由於有超新星的核融合,會有較多金屬元素存在;而較輕的元素(例如氫、氦)則會因為星際介質風的影響,存在於星系外側。但是根據冷流(cold flow)的理論,在宇宙形成初期,許多冷的氣體也會流進星系內部,造成恆星的形成。如果這個冷流確實存在,恆星中間的金屬元素比例就會被稀釋。結果在三個紅位移Z=3的遙遠星系(距離約137億光年,約為大霹靂之後20億年的景象),發現星系中央的金屬元素確實較外圍來得低,顯示冷流現象可能真的存在。

原始論文:
Cresci, G., et al., Gas accretion as the origin of chemical abundance gradients in distant galaxies, Nature, V467, P811–813 (2010).


有冰河保護的山脈

最近更新日期:2010-10-03 | 38 次瀏覽 |

有了冰河的保護,可以讓褶皺山脈不容易被侵蝕。

上圖a,沒有冰河的保護。
上圖b,有冰河的保護。

資料來源:
Braunjean, J., 2010, Earth science: Glaciers shield mountain tops, Nature, V467, P281–282.
http://www.nature.com/nature/journal/v467/n7313/full/467281b.html

Thomson, S. N., M. T. Brandon, J. H. Tomkin, P. W. Reiners, C. Vásquez & N. J. Wilson, 2010, Glaciation as a destructive and constructive control on mountain building, Nature, V467, P313–317.
http://www.nature.com/nature/journal/v467/n7313/full/nature09365.html


彗星的撞擊、生命的起源

最近更新日期:2010-10-03 | 70 次瀏覽 |

過去對於「生命來自於彗星撞地球」的想法,總是存在相當多的爭議。這次科學家利用實驗,模擬出彗星中的物質在劇烈撞擊之下,可能導致氨基酸形成的過程。

上圖a,彗星中原有的分子,在撞擊發生前的狀態。
上圖b,在撞擊發生時,形成了CH3OH的分子。

a,b At the initial conditions (a) and during shock compression at 9 km s−1 (47 GPa) (b). For all of our simulation snapshots, H2O molecules are coloured green, NH3 black, CO light blue, CO2 purple and CH3OH orange. For the atoms, oxygen is red, hydrogen is white, carbon is light blue and nitrogen is dark blue. In (b) the smaller size of the simulation cell results from the shock compression. For clarity we show only atomic sites for C–N bonded species (opaque) formed during shock compression. All other species (transparent) are shown by their bonds only, excluding H+ ions, which are shown as yellow spheres. After shock compression, all of the CH3OH and CO2 are consumed. A small number of H2O and NH3 molecules are still observed, as well as a single CO molecule. Shock compression caused several exotic species to form, including the large carbon chain-like oligomer with several C–N bonds shown in the middle of the snapshot.

資料來源:
Goldman, N., E. J. Reed, L. E. Fried, I.-F. William Kuo& A. Maiti, 2010, Synthesis of glycine-containing complexes in impacts of comets on early Earth, Nature Chemistry, doi:10.1038/nchem.827.
http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.827.html


因為水,岩石圈與軟流圈大不同

最近更新日期:2010-10-03 | 73 次瀏覽 |

造成岩石圈與軟流圈交界處上下之間的差異,可能源自於「水」這種東西的存在。

詳細內容請見:從岩石圈到軟流圈

a, The experimental determination of the vapour-saturated solidus of HZ1 lherzolite composition. The solidus is consistent with earlier work, and our experimental study shows that the inference of much lower solidus temperatures15 (as illustrated) results from misinterpretation of vapour-phase quench as quenched silicate melt. The dehydration solidus—the solidus for pargasite lherzolite without excess water—is also shown, as is a schematic oceanic geotherm which passes through the dehydration solidus at about 90 km, 1,070 °C. b, The experimentally determined water-storage capacity of HZ1 lherzolite along the solidus to more than 4 GPa. We illustrate the sharp reduction in water-storage capacity along the solidus from high values (to 0.5 wt%) in the uppermost mantle, where pargasite is stable, to much lower capacities (approximately 0.02 wt%) in NAMs at 3–4 GPa.

資料來源:
Green, D. H., William O. Hibberson, István Kovács& Anja Rosenthal, 2010, Water and its influence on the lithosphere–asthenosphere boundary, Nature, V467, P448–451.
http://www.nature.com/nature/journal/v467/n7314/full/nature09369.html


還有更多的系外行星!

最近更新日期:2010-10-03 | 54 次瀏覽 |

利用新的重力微透鏡技術,天文學家發現宇宙中類似木星這樣的行星,遠多於過去所預期的數量。

上圖a,當觀測者(箭頭)前方有一顆黯淡的恆星(紅色)經過一顆距離較遠較亮的恆星(黃色)前方時,會觀察到遠方恆星亮度隨時間變化(突然變亮)的現象。
上圖b,若有一顆大型行星會繞行這一顆黯淡的恆星,則當行星繞行到觀測者前方時,會觀察到恆星亮度額外的增強訊號。

資料來源:
Chambers, J., 2010, Extrasolar planets: More giants in focus, Nature, V467, P405–406.
http://www.nature.com/nature/journal/v467/n7314/full/467405a.html


水的危機

最近更新日期:2010-10-03 | 54 次瀏覽 |

隨著氣候變遷與人為開發,地球上對於人類的用水以及河流生物多樣性的威脅也日益增加。印度、中國、歐洲以及美國中部,是目前危險程度最高的地區。


人類用水危機

上圖中紅色代表危險,藍色代表安全,灰色代表那裡本來就沒甚麼水。

資料來源:
Vörösmarty, C. J., P. B. McIntyre, M. O. Gessner, D. Dudgeon,A. Prusevich, P. Green,S. Glidden, S. E. Bunn, C. A. Sullivan, C. Reidy Liermann& P. M. Davies, 2010, Global threats to human water security and river biodiversity, Nature, V467, P555–561.
http://www.nature.com/nature/journal/v467/n7315/full/nature09440.html


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