Question

Several fish species became extinct millions of years ago. The graphs provided below show the distribution of fossils of these fishes as they occur in several undisturbed layers of sedimentary rock observable in a cliff face. Respond to ALL 4 PARTS below: Explain why the distribution of the fossils in figure 1 support the hypothesis that the extinction of these species was a result of a sudden environmental change. Describe an environmental change that could have produced this kind of fossil distribution. Explain why the distribution of the fossils in figure 2 supports the hypothesis that the extinction of these species was a result of a gradual environmental change. Describe an environmental change that could produce this kind of fossil distribution.

Answer 1

If the graphics are the ones found in http://oh.portal.airast.org/core/fileparse.php/3094/urlt/OST_Practice_LP_G8Sci.pdf then the answers are the next:

a) The drop of frequency of fossils in figure 1 indicates that these species were present in a rock layer and absent in the next, which means that the dissapearance of the species in the timeline was sudden.

b) An iceberg detachment could cause a sudden drop of salinity in the fishes' environment and affect the sea currents they depended on. So the complete population would perish in a few hundred years, which would be a sudden drop to cero in a rock layer graph.

c) Figure 2 tells us that there was a decreace in fossil abundance over a long period of time that occupied several rock layers. So undoubtedly an extintion happened, but it was gradual.

d) A global increase or decreace in temperature could cause in fish a similar effect than that shown in figure 2. If the change is just barely outside their tolerance niche, and the species does not adapt to the new environmental conditions, each generation there would have less and less fish because some couldnt tolerate the conditions, making the extintion of the fishes species a gradual affair lasting thousands of years.