Julianne Zedalis; John Eggebrecht

Science Practice Challenge Questions

69.

Twenty targets for the protection of biodiversity by 2020 were established by the 2010 Convention on Biological Diversity. Midway to the target date it is widely agreed that the goals will not be met. The 2016 Living Planet Report from the World Wildlife Federation claims global populations of animals fell by 58 percent between 1970 and 2012 and extrapolates the loss by 2020 to 67%. E.O. Wilson's estimate of the current extinction rate is three species per hour. Geologic periods are defined by mass extinctions. The proposed name for the current geological period is the Anthropocene (Waters et al., Science, 2016).

During the current period of mass extinction, human activities are driving loss of habitat and climate change. Climate change during the last 500,000 years is a direct consequence of rising atmospheric CO₂ levels, as the graph shows. The relative abundance of O¹⁶ and O¹⁸ isotopes can be used to infer temperature because as temperature increases the lower mass isotope is enriched in the atmosphere (objects with a smaller mass have a higher velocity at equal molecular kinetic energy that is proportional to temperature).

This graph shows carbon dioxide concentration in P P M on the left y-axis, which ranges from 150 to 350. It also shows Temperature difference on the right Y axis, which ranges from negative 10 to negative 6. The X axis is titled years before present and ranges from 450000 to 50000. The blue trend line shows temperature in degrees centrigrade compared with the 1960 to 1990 baseline. The red trend line shows atmospheric carbon dioxide in parts per mission. Both the red and the blue lines cycle up and down four times across the graph with peaks occurring at about equally spaced intervals. The first peak is between 45000 and 400000 and the last peak is right before 0 years before present. The peaks reach into the upper portion of the graph for both carbon dioxide and temperature. The five peaks are separated by troughs where temperature and carbon dioxide both drop to near the bottom of the graph. — Figure 35.31

The role of humans in the last great extinction, the Holocene Extinction, during which the megafauna such as the wooly mammoth, the wooly rhinoceros and the giant deer disappeared, has long been debated. Did we hunt these creatures to extinction? By examining all available DNA evidence, Cooper et al. (Science, 349, 2015) have compared time extinction intervals with these oscillations of climate as shown in the table.

Animal	Label	Loc- ation	Begin extinct event (TYA)	End extinct event (TYA)
Bear	a	Ber- ingia	24	21
Bison	b	Europe	35	32
Rhino- ceros	c	Britain	36	32
Rhino- ceros	d	Russia	14	13
Horse	e	North America	15	13
Horse	f	Ber- ingia	43	38
Mast- odon	g	North America	12	11
Mam- moth	h	Europe	13	12
Mam- moth	i	Eurasia	11	10
Musk Ox	j	Eurasia	48	44
Deer	k	Europe	13	12
Cave Lion	l	Ber- ingia	14	12
Cave Bear	m	Europe	29	27

Table 35.1 TYA = thousand years ago

Additionally, the data shown in the graph below are obtained from ice cores. The deeper the sample, the older the sample. The percent departure from the current O¹⁸ percentage that is graphed above is a measure of temperature relative to the present temperature. The higher the isotope concentration, the higher the average temperature of the ocean.

This plot shows delta oxygen 18 percent on the Y axis and thousand years ago on the x axis, ranging from 0 to 50. The plot line fluctuates heavily between 1- and 50, with a slight dip in the fluctuations occurring between 25 and 30 thousand years ago. One of the higher peaks is labelled with an A and occurs between 20 and 25 thousand years ago. — Figure 35.32

A. Refine the graph by adding the interval of time of extinction with a label drawn from the table as shown by “a”.

B. Analyze these data in terms of the clustering of extinction events.

C. Based on your analysis, explain how ecosystems have changed during the last 40,000 years, changed and identify the factor that caused these changes.

D. Based on the correlation between Earth’s temperature and the concentration of CO₂ in the atmosphere, predict what will happen to animal populations in the future.