TEORIES OF MASS EXTINCTIO大規(guī)模滅絕理論及

1、 takes place in repeating cycles, i.e. warm age followedby ice agegraphic illustration of more recent warming and cooling cycles. change in climatevikingsknights30 year warindustrial eralittle ice ageaverage warm ageyearsyears volcano activity a possible cause for the cooling of the earth due to lar

2、ge volumes of dust blown into the atmosphere that blocks out the suns rays. reduces solar radiation.2.heating of the atmosphereexample: extinction in gondwanaland (clarens in the free state) a mild climate with plenty of water in large lake systems, to a hot, dry desert climate. warmer climate leads

3、 to change in environmental food chains. tectonic plates led to changes in environments disease change in climate - influences presence of disease causing organisms in environments and their effect on the survival of other organisms. also theory of extraterrestrial viral and bacterial invasionextrat

4、errestrial theories explosion of a stars influence on earth radiation levels and destroys ozone layermay have influenced extinctions (no scientific proof as yet) meteorite / asteroid collisions with earthmeteorite large rocklike mass that falls from outer space onto earth larger than 1 km (vredefort

5、 and parys)asteroid off course orbiting fragments of a failed planet in the asteroid belt between mars & jupitermeteor small fragments, burn up in space, called shooting starscomet revolves in elliptic orbit around the sun, has solid nucleus + gaseous tailgamma radiation from dying starsmeteorit

6、es meteors (shooting stars) burn and glow when they enter earths atmosphere. most disintegrate into ashes and debris. some remain intact, known as meteorites, to create craters on earth. can destroy life forms by shutting off sunlight for months / years.meteorites and extinction growing evidence tha

7、t meteorites are responsible for some major mass extinctions. meteorites may have added the final blow to species that were already weakened by global temperature changes, etc.what happened to dinosaurs? scientific evidence: meteorite impact melted rocks in 200km diameter crater near mexico. sedimen

8、ts deposited by enormous tsunamis (tidal waves) along coastline. caused acid rain and severe global cooling. 70% of known fossils, including dinosaurs, wiped out (65 ma).impact in gulf of mexico200 km diameter crater in mexican gulf (near chicxulub)caused by 10km diameter meteorite impact of 65 mill

9、ion years ago.impact caused acid rain, ash that blocked out the sun for months, severe global cooling (nuclear winter).increase in atmospheric co2, resulting in global warming, final blow to dinosaurs & many other cretaceous species.dinosaur extinctionvredefort dome crater 10 km in diameter. imp

10、act speed of 10 15 km /sec. 16 km into earths crust. blast of impact caused 70km3 of rock to be vapourised and to spread into the atmosphere. location:100 km south of johannesburg between vredefort and parys. 5 major extinctions1. end of ordovician 2. end of devonian3. end of permian4. end of triass

11、ic5. end of cretaceous time line of each extinction?which was the most severe?which was the least severe?which is most recent?sixth extinction the impact of man on earth human overpopulation current rate of extinction of species estimated at three species / hour or about 30 000 species per year.glob

12、al warming the big melt down rising ocean levels as polar ice caps and glaciers melt increasing global temperatures change in seasonal patterns more frequent occurrence of weather extremes e.g. increase in droughts & floods migration of disease vectors for malaria, bilharzia and cholerahuman inf

13、luence on the drastic increase in extinction of species industrial activity pumping greenhouse gases into atmosphere climate change pollution change of large parts of natural environments into food-producing agricultural areas & living spaces due to overpopulation and widespread habitat destruct

14、ion.recent extinctions bluebuck quagga many frog species near extinction of bontebok and sable antelope many cycad species some proteas and bulbs.kwaggasomething to think aboutthe modern climate is depicted by a question mark, reflecting the uncertainty of the future climate. if humans were not pres

15、ent on earth, the climate would likely cool off into an ice age, as it has many times in the past. however, humans are disrupting earths carbon cycle by burning fossil fuels, and releasing greenhouse gases into the atmosphere. by the hansen et al. (1988) scenario a, the climate could warm 7.2f (4c) by the year 2050 should a worst-case materializemclean, d. m., 1991, a climate change mammalian population collapse mechanism, in kainlauri, e.,