Development of a widely accepted chronology for the arrival of humans has been equally difficult, and it was only with the development of optically stimulated luminescence dating that a human presence in Australia was confirmed at 53,000 to 60,000 years ago. Older dates for a human presence in Australia have now been shown to be erroneous .
The importance of Australia as a separate natural laboratory in which to test extinction theories lies in the fact that humans arrived there much earlier than they arrived in the other continental areas (the Americas and northern Eurasia) that experienced substantial megafaunal extinction. What Miller et al. have shown is that the extinction of Genyornis occurred simultaneously across southeastern Australia (indeed probably right across the continent) about 50,000 years ago. This is very close to the presently accepted time of arrival of humans in Australia. It was also a period of modest climate change, well before the dramatic climatic fluctuations of the terminal Pleistocene. The data of Miller et al., therefore, support those who see human hunting rather than climate as causing the extinction of the megafauna.
Genyornis was a ponderous bird, around 80 to 100 kg in weight, about twice as heavy as the living emu and cassowary. It was an inhabitant of Australias inland plains and some coastal regions, but its legs were relatively short and thick, suggestion that it was a slower runner than the emu. Proponents of humancaused extinction suggest that it is just such characteristics that made the megafauna vulnerable to human hunting.
A new school of thought has recently established itself in the extinction debate. It advocates the idea that a combination of human impact and climate change was responsible for the extinction of the worlds megafauna. The new Genyornis data also weaken that argument, for the following reason. Fifty thousand years ago, Australia was experiencing mild cooling; 11,000 to 12,000 years ago, the Americas were experiencing rapid warming. These disparate climatic conditions, all coincident with megafaunal extinction, suggest that whatever was happening with climate, it was bad for the big animals. Under these conditions, the hybrid model becomes indistinguishable from the humancaused extinction model for the influence of climate becomes extremely weak, and only the arrival of humans is important in predicting extinction.
The last word “megafauna” in Paragraph 2 most probably means
A  birds.  B  plants.
C  big animals.  D  small animals.
Genyornis was vulnerable to human hunting because it was
A  a delicacy.  B  very weak.
C  very small in size.  D  clumsy.
 How many models have been put forward for the extinction of Genyoris?
A  One.  B  Two.
C  Three.  D  Four.
That Australia experienced mild cooling and the Americas rapid warming suggests that
A  the climatic conditions were unfit for Genyornis to live.
B  Genyornis were highly adaptable to different climatic conditions.
C  The two climatic conditions were both bad for Genyornis.
D  The climatic conditions had nothing to do with the extinction of Genyoris.
The selection is mainly about
A  the debate over the time of the human presence in Australia.
B  the relationship between the human presence and magafaunal extinction.
C  the relationship between human activities and climatic changes.
D  the debate over factors causing megafaunal extinction.