很多考生会抱怨托福阅读时间不够，还没完全理解文章就做题，正确率不高。其实这是我们对托福阅读素材不熟悉造成的，下面小编整理了一下托福阅读考试最新的素材，希望能帮助大家更加快速高效的备考托福。

　　托福阅读素材：始新世气候变暖

　　内容回忆：

　　本文一共五段。第一段大致介绍了一下 Eocene Warming 的由来及两种可能的成因。第二段具体阐述了第一种成因，即洋流的改变。但是该种原因由难以解释的地方。第三段具体提及热带地区的太平洋是 Eocene Warming 发生的可能原因之一。第四段提出了一个问题： Earth 是不是进入了永远的 Warming 时代?段末给予否定。最后一段则说 Eocene Warming 的成因可能和洋流无关，和天空有关，但是需要进一步探究。

　　参考阅读：

　　The Paleocene-Eocene Thermal Maximum (PETM) at 55 million years before present is arguably the best ancient analog of modern climate change. For this reason, we devote considerable attention to the event here. The PETM involved more than 5oC of warming in 15-20 thousand years (actually a little slower than rates of warming over the last 50 years), fueled by the input of more than 2000 gigatons (a gigaton is a billion tons!) of carbon into the atmosphere. The PETM was associated with the largest deep-sea mass extinction event in the last 93 million years and remarkable diversification of life in the surface ocean and on land.

　　The evidence for warming comes from a variety of sources, the most compelling of which is the oxygen isotopes of planktonic and benthic forams in deep sea cores. These data suggest significant warming of 6-8 oC of ocean surface waters at a range of latitudes, as well as of deep waters.

　　Corresponding to the oxygen isotope shift is a large and negative 4 to 5 per mil change in carbon isotopes that is used to define the geological extent of the event. The isotope excursion has been identified in sediments deposited in the ocean and those laid down in terrestrial environments such as lakes and rivers. In particular, the excursion in terrestrial sediments allows us to correlate the changes that occurred on land during the PETM with those that took place in the ocean.

　　The content of CO2 in the atmosphere increased 3-4 times during the PETM. As a consequence, surface ocean temperatures at the peak of the event were extremely warm, especially in the high latitudes. Off the coast of Antarctica, a location today that is close to freezing, the oceans were about 20oC at the peak of the PETM! Imagine jumping into the ocean from Antarctica today! Tropical ocean temperatures were likely a few degrees warmer than at present. The PETM was also associated with major changes in the properties of the deep ocean. Unlike today when deep ocean waters are characterized by temperatures close to freezing, PETM deep waters were 10-15o C.

　　Likely the cause of these warm deep waters was that they came from different surface ocean locations than they do today (see Module 6 for more detail on the sources of modern deep waters), combined with the warming that took place in the surface ocean. As warmer waters hold less oxygen than cold waters, PETM deep waters in many locations likely were possibly close to a condition that is known as hypoxia (we will learn more about this in Module 6). Finally, the input of so much CO2 into the ocean caused ocean waters to become more acidic and led to a condition known as ocean acidification. Acidification of the deep ocean during the PETM is well accepted and is observed by complete dissolution of all CaCO3 shells that rained down on the sea floor.

　　更多托福阅读考试信息

　　了解环球教育托福课程