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Earth Science
Column of Time

Earth Science
Earth Science


Column of Time
Print Column of Time Reading Comprehension


Reading Level
     edHelper's suggested reading level:   grades 9 to 10
     Flesch-Kincaid grade level:   9.09

Vocabulary
     challenging words:    benchmark, gastrolith, mega-annum, life-form, paleontologists, eons, geologic, sedimentary, absolute, imprint, majority, calculate, better, representation, dating, currently
     content words:    Paleozoic Era, Mesozoic Era, Cenozoic Era


Column of Time
By Trista L. Pollard
  

1     The secret of our planet's history lies buried in millions of year's worth of sediment. Every fossil, amber, imprint, and gastrolith waits to be studied by eager paleontologists. Before these scientists could draw conclusions about the Earth's past, they needed to develop a standard scale. This scale would help paleontologists to describe the sequence and length of our planet's geological and environmental changes.
 
2     The geologic time scale serves as a benchmark for scientists when they study the Earth's development. Most if not all fossils are found in sedimentary rocks. Scientists during the 19th century used superposition to estimate the relative age of rock structures worldwide. However, like a library with thousands of books, there was not one area of Earth that represented the entire geological history of Earth. Based on observations, a standard geologic column was designed. The geologic column is a representation of the Earth's history. The rocks at the top of the column are the youngest.
 
3     The characteristics of each layer within the column are determined by the type of rocks and fossils found in each layer. You would find the fossils of more modern plants and animals in the upper layers of the column. Plant and animal fossils found in the lower layers of the column are that of extinct species. Scientists have determined that these fossils may be millions of years old. During the last century, it has become easier to calculate absolute age by using the geologic column. This scale, however, has been used by scientists when radiometric dating cannot be used to calculate the age of a rock. They compare the rock layers they are studying with rock layers that are similar in the geologic column. This layer would contain either the same fossils or have the same relative position. The layers would have formed during the same time period if their characteristics matched.

Paragraphs 4 to 6:
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