GRE Reading Comprehension
Home > GRE Test > GRE Reading Comprehension Questions
Next steps
- Use your browser's back button to return to your test results.
- Do more GRE Reading Comprehension Questions.
Source: NO3
The primary method previously used by paleontologists to estimate climatic changes that occurred during Pleistocene glacial cycles was the determination of 18/O16/O ratios in calcareous fossils. However, because this ratio is influenced by a number of factors, the absolute magnitude of the temperature difference between Pleistocene glacial and interglacial cycles could not be unequivocally ascertained. For example, both temperature fluctuations and isotopic changes in seawater affect the 18O/16O ratio. And. since both factors influence the ratio in the same direction, the contribution of each to the 18O/16O ratio cannot be determined.
Fortunately, recent studies indicate that the racemization reaction of amino acids can be used to determine more accurately temperatures that occurred during Pleistocene glacial cycles. Only L-amino acids are usually found in the proteins of living organisms, but over long periods of geological time these acids undergo racemization, producing D-amino acids, which are not found in proteins. This reaction depends on both time and temperature thus, if one variable is known, the reaction can be used to calculate the other.
The information in the passage can be used to answer which of the following questions?
Ⅰ Do temperature variations and isotopic changes in seawater cause the 18O/16O ratio to shift in the same direction?
Ⅱ What are the methods used to determine the18 O/16O ratio?
Ⅲ Is the study of raceminzation reactions useful in estimating climatic changes that occurred during Pleistocene glacial cycles if only one of the two important variables is known?
- A Ⅰonly
- B Ⅰand Ⅱ only
- C Ⅰand Ⅲ only
- D Ⅱand Ⅲ only
- E Ⅰ,Ⅱ,and Ⅲ