![]() Because, the unknown fossil, the red sponge, was found with the fossils in fossil assemblage B it also must have existed during the interval of time indicated by the red box. Fossil assemblage B includes the index fossils the orange ammonite and the blue ammonite, meaning that assemblage B must have been deposited during the interval of time indicated by the red box. In this figure, the unknown fossil, a red sponge, occurs with five other fossils in fossil assemblage B. If both the blue and orange ammonites are found together, the rock must have been deposited during the time interval indicated by the red box, which represents the time during which both fossil species co-existed. For example, there is a specific interval of time, indicated by the red box, during which both the blue ammonite and orange ammonite co-existed. Using the overlapping age ranges of multiple fossils, it is possible to determine the relative age of the fossil species (i.e., the relative interval of time during which that fossil species occurred). The position of the lower arrowhead indicates the first occurrence of the fossil and the upper arrowhead indicates its last occurrence – when it went extinct. In the figure, that distinct age range for each fossil species is indicated by the grey arrows underlying the picture of each fossil. This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.įossils occur for a distinct, limited interval of time. Third, magnetism in rocks can be used to estimate the age of a fossil site. Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Second, it is possible to determine the numerical age for fossils or earth materials. Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event. There are three general approaches that allow scientists to date geological materials and answer the question: "How old is this fossil?" First, the relative age of a fossil can be determined. However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared. ![]() By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time. Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.įor example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years. The age of the fossil must be determined so it can be compared to other fossil species from the same time period. However, by itself a fossil has little meaning unless it is placed within some context. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.Ī fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
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