
生物灭绝教学讲义.ppt
44页对生物集群灭绝的初步认识Mass Extinction,,生物大灭绝( Mass Extinction)的定义:,依据于化石记录,在一个比较短的时间(1-2Ma?)内,大量的生物物种绝灭通常是生物界对一次大规模的快速的全球性的事件的响应显生宙生物集群灭绝事件,地球历史中出现过五次大的生物大灭绝事件,一,陨石撞击( impact ),K-T:淡水生物达97%、海洋浮游微生物为58%、海洋底栖生物为51%、海洋游泳生物为30%除了恐龙灭绝之外,曾在前4次大绝灭中都得以幸存的菊石最终还是灭绝了而由于某种原因,某些物种却基本没有受到影响,鳄鱼、海龟、蜥蜴、哺乳动物以及鸟类都顺利渡过了这场危难恐龙及其同类的消失为哺乳动物以及人类的登场提供了契机What Killed the Dinosaurs?,小行星带,小行星带(Asteroid belt),Earth has the smallest number of impact craters(陨石坑)among terrestrial planets . WHY? Few impact craters are well preserved on the Earth surface.,已发现的陨石撞击坑约160个,Barringer Meteor Crater, Arizona(亚利桑那州), U.S. (49,000 yrs),One of the worlds best known craters First recognized impact crater on Earth (1928) Less than 1 mile across, it was created about 49,000 years ago Formed by an iron meteoroid - lots of melted droplets and solid pieces of an iron-nickel material have been recovered in the area,,艺术家笔下K-T撞击事件,地球物理资料(重力),,撞击坑,证据,,陨石,,地球物质,撞击灰尘,后期微体化石,与恐龙同时代的微体化石,陨坑附近物质沉积,白垩纪/第三纪 (KT) Boundary,Raton Basin, NM, USA,Tertiary,Cretaceous,界限两边的化石发生明显的变化,Paleogene (“Tertiary”),Cretaceous,,泥岩层,,Initial Evidence of Bolide Impact: Iridium,Gubbio, Italy,Cretaceous,Paleogene (“Tertiary”),,Iridium-rich boundary clay layer,,Iridium “spike”: High iridium concentrations from asteroid/comet,铱异常(高的峰值),The KT Boundary(白垩纪/第三纪),K-T layer (black), also contains soot(碳灰) (from fires), spherical rock droplets(球状的岩石颗粒) and shocked quarts (撞击形成的石英) (commonly formed in impacts) and comprises high abundances of iridium, gold, osmium, and platinum (more common to meteorites (陨星) than to Earth).,富铱的泥岩层(比较一致的全球分布) 铱元素在地球上含量很少,在地球外的某些星体上含量相对较多,,Shocked Quartz in K-T Boundary Clay High pressures cause what is known as shock metamorphism, this deforms the structure of the quartz and creates parallel laminar ripples. It is found all over the world, not just locally. Has only been observed at meteorite impact sites(陨坑) and nuclear test sites(核试验) No other process on the planet creates this type of quartz.,Tektites, glass beads(玻陨石,玻璃珠)found in boundary sediments,Due to melting of rock by energy of bolide(陨星)(asteroid小行星 or comet彗星) impact ?,Glass found in boundary sediments of Gulf of Mexico,代表了熔体快速降温的过程,Computer model of effects of K-T Impact Winter,撞击事件后,地球至少持续了六个月的黑暗,,,,,,二:大的火山活动(CFB,LIP等),Deccan Traps Volcanism,德干高原大陆溢流玄武岩省,About 65 million years ago, the mantle plume that gave rise to the Reunion hotspot volcano burned its way through earths crust, flooding western India and surrounding areas with the Deccan Traps flood basalts.,溢流玄武岩火山作用,The result of great volcanic activity associated with rising heat plumes from mantle (核幔边界D”),Deccan Traps (India) record eruption of more than 500,000 million cubic km of basaltic lava over perhaps about 5 million years (but began before end of Cretaceous Period).,溢流玄武岩火山作用似乎与生物集群灭绝有关,但并不是所有的生物集群灭绝事件都与火山作用有关,三,大的冰期 (Ice Ages and Extinctions),ice age,,,,,,,ice age,There is no tight correlation between ice ages and mass extinctions,1,晚奥陶世的冰川作用引起海平面下降和较冷的温度。
2,海平面下降导致浮游生物和底栖生物的生存范围大量减小Causes of Permian Ice Age?? Large land mass over the south pole global equatorial to polar oceanic circulation blocked,四:大的海平面下降,晚奥陶世的冰川作用引起海平面下降和较冷的温度 海退导致陆表海消失,底栖生物生境消失,或是陆棚海面积变小,生物生存范围缩小,变得拥挤,竞争加大窄生境性生物大量绝灭 二叠纪末联合古大陆,全球陆地区被海水的覆盖率由二叠纪初的40%降至二叠纪末的10%以下海进海退 证据:全球同层位的13C 的异常 正偏:海进,生物繁盛,13C 在海洋无机界中富集 负偏:海退,生物衰落,12C 在无机界富集更多 海进海退多数是由于冰川活动,或是大陆板块运动造成的d13C isotopic shift(Italian Alps),五:超大陆的汇聚,1,泛大陆的聚合导致大规模的全球海退事件;,二叠纪末Pangaea联合古陆形成,Deep-sea anoxic interval (Japan),六:海水环境的变化,缺氧事件 在显生宙的五次生物集群灭绝期,沉积学,古生物学,地球化学等资料都显示出了缺氧事件,如在二叠纪-三叠纪接线附近发现了绿硫细菌的标志化合物,绿硫细菌分子化石记录当时海水环境缺氧,并且在透光带也富含硫化氢,还有一些生物集群灭绝被认为是海水天然气水合物的释放,晚泥盆世裸子植物、高大乔木、多重结构森林出现化学和生物化学风化盛行真正意义土壤广为发育地表径流向滨、浅海输送的有机物和营养物质增多陆表海由超寡营养到富营养化浮游植物和浮游动物等低等菌藻微生物繁荣频繁的赤潮海洋水缺氧导致中低纬度浅水海相生物集群绝灭。
地质界限之交的海洋不是死难的海洋,而是菌藻微生物的伊甸园 广西的近岸碳酸盐海域藻类大量繁殖和高度富集,海水富营养化,缺氧,高盐度,碳酸盐碳同位素正偏和生物分异度锐减, 暗示F-F(晚泥盆纪弗拉斯期法门期)之交为赤潮的多发期七,其它因素:生物因素, 超新星的爆发等,存在问题 1,火山(大陆溢流玄武岩)与陨石撞击是不是有关系(海平面上升与下降,大的冰期,海洋环境的变化,超大陆的拼合裂解等)?如果有,怎样的关系? 2,为什么一部分生物灭绝而另一些生物却幸存了下来?它们以什么样的方式幸存下来?,,自寒武纪以来,在地球出现过的99%的生物已经消失了,但是有些生物却幸存了下来这是一种腕足动物(舌形贝属),生活在海洋的沙泥,垂直的洞穴中,自从志留纪以来,形态和结构一直没有发生变化,Despite their name, these animals are not crabs(螃蟹)at all but are related to scorpions(蝎子), spiders(蜘蛛), and extinct trilobites(三叶虫),马蹄形螃蟹(活化石),栖息于海岸,自从奥陶纪以来形态和结构没有发生明显的改变,这是它底面腹部的结构。
了解不同层次,不同水平之间,复杂的相互作用关系,作用路径及生物自身个体的特点等,是解决生物集群大灭绝的关键,这有依赖于古生物学,地球化学,地球物理学,构造地质学,天文学,生命科学等多学科的努力谢谢!,。












