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：化石记录

　　第一段人们通过化石记录可以了解生命的历史：人们通过沉积岩来研究化石并记录。第二段讲到古生物学者和 Archeologist 通过放射性同位素来研究化石;但这种方法并不适用所有的化石研究。第三段讲放射性同位素这种方法研究化石的缺陷;第四段讲到化石记录会有 biases.常见的有三种，一种是有些生物比较容易有化石，第二种是地质的原因，第三种是研究者有 biases unintentionally.

　　参考阅读：

　　Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better.[19] Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments.[19]

　　Stratigraphy

　　Consequently, palaeontologists rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record.[20] Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages.[21] Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy. For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period.[22] If rocks of unknown age have traces of E. pseudoplanus, they have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. [23] Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching rocks of the same age across continents. [24] Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier.

　　It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at a constant rate. These "molecular clocks", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved,[25] and estimates produced by different techniques may vary by a factor of two.[26]

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