Huge areas of the Amazon rainforest were grassland until just 2,000 years ago, which has been revealed.

Researchers say the find sheds new light on the Amazon’s history - and show it was a savanna rather than the high forest it is today. They believe much of the area was grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforest form, according to a study that challenges common belief that the world’s biggest tropical forest is far older.

The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have sped up the growth of forests by killing indigenous people farming the region, the scientists wrote in the US journal Proceedings of the National Academy of Sciences (PNAS). 

“The dominant ecosystem was more like a savanna than the rainforest we see today,” John Carson, lead author at the University of Reading in England, said of the findings about the southern Amazon. The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth’s orbit around the sun, led to growth of more trees starting about 2,000 years ago. The “findings suggest that rather than being rainforest hunter-gatherers, or large-scale forest clearers, the people of the Amazon from 2,500 to 500 years ago were farmers,” the University of Reading said in a statement.

Carson said that perhaps a fifth of the Amazon basin, in the south, may have been savanna until the shift, with forests covering the rest. In one lake, Laguna Granja, rainforest plants only took over from grass as the main sources of pollen in sediments about 500 years old, suggesting a link to the arrival of Europeans.

And understanding the forest could help solve puzzles about climate change. The Amazon rainforest affects climate change because trees soak up heat-trapping carbon dioxide as they grow and release it when they rot or are burnt. Brazil has sharply slowed deforestation rates in recent years.

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1.In what way does the study challenge people’s traditional belief?

A Understanding of climate change.

B History of the Amazon rainforests.

C Time of the arrival of Europeans.

D Shifts in the earth’s orbit around the sun.

解析：选B。细节理解题。根据文章第二段末句…common belief that the world’s biggest tropical forest is far older可知，人们传统的看法是亚马逊热带森林历史悠久，远远超过两千年。而研究发现，亚马逊热带丛林两千年前还是大草原，地球绕日轨道的变化使该地区气候湿暖，从而进入热带丛林生长阶段。

2.What was the effect of the arrival of Europeans?

A The rainforests growth sped up.

B More people farmed the area.

C Indigenous died out.

D The climate became wetter.

解析：选A。细节理解题。根据文章第三段The arrival of …may also have sped up the growth of forests可知，哥伦布航行大西洋加快了亚马逊热带森林的增长。原因是大草原上的农民因为感染欧洲疾病大批死去，农耕迟滞，给热带森林生长蔓延提供了条件。

3.How does the author think about Columbus’ crossing the Atlantic in 1492?

A Significant.

B Necessary.

C Valueless.

D Destructive.

解析：选D。推理判断题。根据文章第三段European diseases…killing indigenous people farming the region可知，欧洲居民并不是带来了什么先进的文明，而是具有毁灭性的传染病，给土著居民带来了灾难。由此判断，作者认为哥伦布航行大西洋是具有破坏性的行为。

4.What do we know from the pollen in the sediments in Lake Laguna Granja?

A The indigenous people lived as hunters 500 years ago.

B Large number of trees were planted by the Europeans.

C The indigenous people stopped growing crops on the savanna.

D The climate in this region started to become wetter.

解析：选C。细节理解题。根据文章第五段…rainforest plants only took over from grass …about 500 years old可知，五百年前，欧洲人来到亚马逊大草原，土著居民由于被感染欧洲传染病大批死亡，农耕停止，热带森林植物覆盖了草原植被。这些沉积物说明了当时的环境是大草原。故选C。

5.Why does Brazil slow the deforestation rate?

A Because Brazil wants to have more land for farming.

B Because Brazil intends to help prevent global warming.

C Because Brazil attempts to understand what causes climate change.

D Because Brazil wants to turn the rainforest into savanna.

解析：选B。推理判断题。根据最后一段主题句…solve puzzles about climate change可知，保护森林有利于遏制气候变化。巴西大幅度减少森林砍伐，其目的是为了保护环境，利用森林解决气候变暖的问题。