Question

Scientists use index fossils to identify the times at which unidentified fossils and certain sediments were deposited. They hypothesize that if a particular fossil is found near an index fossil, in the same layer of rock, then the two fossils were likely from the same time period. The shorter the lifespan of the index fossil species, the more precisely scientists are able to correlate that species with a particular era. Therefore, it is not surprising that ideal index fossils are from shortlived, common, and easy-to- identify species. Which of the following is an example of the effective use of index fossils? A. Scientists fix the time that Mesolenellus hyperborea existed in the late Nevadella era, because they find Mesolenellus hyperborea near and in the same level of rock as Limniphacos perspiculum, a recognized index fossil that existed in that period. B. Scientists determine that Mesolenellus hyperborea were probably mud bottom- dwellers, because hyolitha, which existed during the same time period as Mesolenellus hyperborea, were also bottom dwellers. C. Scientists hypothesize that Mesolenellus hyperborea were wiped out by a sudden climate change that occurred at the end of the Devonian period, when many other trilobites were wiped out. D. Scientists determine that Mesolenellus hyperborea did not exist in Iceland, because Petrianna fulmenta, a similar trilobite, did not exist in Iceland.

Short answer

Option A is the correct answer, as it demonstrates the effective use of index fossils. In this case, scientists are using the recognized index fossil, Limniphacos perspiculum, to determine the time period of Mesolenellus hyperborea by finding them near each other and in the same level of rock. This helps them fix the time that Mesolenellus hyperborea existed in the late Nevadella era, which is an example of the effective use of index fossils.

Step-by-step solution

Identify the properties of ideal index fossils

An ideal index fossil should have the following properties: 1. Short lived. 2. Common. 3. Easy to identify.

Analyze each option

We will analyze each option and see which one demonstrates the effective use of index fossils. A. Scientists fixing the time that Mesolenellus hyperborea existed in the late Nevadella era because they find Mesolenellus hyperborea near and in the same level of rock as Limniphacos perspiculum, a recognized index fossil that existed in that period. B. Scientists determine that Mesolenellus hyperborea were probably mud bottom-dwellers because hyolitha, which existed during the same time period as Mesolenellus hyperborea, were also bottom dwellers. C. Scientists hypothesize that Mesolenellus hyperborea were wiped out by a sudden climate change that occurred at the end of the Devonian period, when many other trilobites were wiped out. D. Scientists determine that Mesolenellus hyperborea did not exist in Iceland because Petrianna fulmenta, a similar trilobite, did not exist in Iceland.

Choose the correct option

Option A is the correct answer, as it demonstrates the effective use of index fossils. In this case, scientists are using the recognized index fossil, Limniphacos perspiculum, to determine the time period of Mesolenellus hyperborea by finding them near each other and in the same level of rock. This helps them fix the time that Mesolenellus hyperborea existed in the late Nevadella era, which is an example of the effective use of index fossils.

Key concepts

Fossil Correlation

Fossil correlation is a crucial technique used by geologists and paleontologists to date rock layers and understand Earth's history. By using index fossils—remains of organisms that lived for a relatively short period but were widespread and abundant—scientists can correlate rock layers across different regions.

Consider the example of index fossil Limniphacos perspiculum, which existed during the late Nevadella era. If Mesolenellus hyperborea fossils are found in the same layer as Limniphacos perspiculum, scientists can reasonably conclude that these two species lived during the same time. This conclusive evidence comes from the fact that index fossils like Limniphacos perspiculum have distinctive characteristics that make them easy to identify and match across different geographic locations.

Geological Time Scale

The geological time scale is a system of chronological dating that relates geological strata to time. It's like a massive calendar for Earth's history, spanning billions of years. The divisions of the time scale—such as eras, periods, and epochs—are based on significant changes in Earth's geology, climate, and biotic conditions, often marked by mass extinctions or the emergence of new species.

The discovery of index fossils in particular strata helps geologists pinpoint the temporal boundaries of these divisions. For example, the presence of Limniphacos perspiculum within a rock layer tells us that this layer was formed during the late Nevadella era, providing a significant marker on the geological time scale.

Stratigraphy

Stratigraphy is the study of layered sedimentary rocks, or strata, and is a key branch within geology. This technique involves analyzing the arrangement and distribution of layers to interpret the Earth's history. Each layer, or stratum, can reveal information about the environmental conditions at the time of its formation. Paleontologists use stratigraphy to understand the chronological sequence of fossil deposits.

Index fossils are an integral part of stratigraphic study because they help in dating the rocks more precisely. For instance, if a rock layer contains the index fossil Limniphacos perspiculum, scientists can assign a Nevadella-era age to that layer, helping to build a chronological framework for other fossils and geological events in that stratum.

Paleontology

Paleontology is the scientific study of life in the geologic past, particularly through the examination of fossils. This field reveals the diversity of ancient life, evolutionary processes, and past climates. Paleontologists often rely on index fossils to ascertain the ages of fossilized remains.

By identifying index fossils like Limniphacos perspiculum in various rock layers, paleontologists can create a more accurate picture of the biodiversity and ecological conditions of specific geological periods. This correlation also aids in the study of evolutionary trends over time, such as the sudden climate change hypothesized to have caused the extinction of species like Mesolenellus hyperborea during the Devonian period.