The Earth Has a Future Steven Ian Dutch University of Wisconsin–Green Bay, Green Bay, Wisconsin 54311-7001, USA ABSTRACT seismicity, volcanism, plate tectonics, astronom- give us no justifi cation for attempting more than ical changes, and human effects. Most processes one signifi cant digit of precision, and in many An alternative to visualizing geologic time or events are discussed only at the time scales cases no more than an order of magnitude. by looking into the past is to look into the most appropriate to their rates or frequencies. In most cases it does not make statistical future. Even geologically short future time For brevity and clarity, once sources have been sense to attach error bars or confi dence inter- scales completely outstrip our ability to fore- cited for one time scale, they will not be cited vals to these estimates. For example, Graymer cast changes in human society, whereas most for similar extrapolations at longer scales. Given et al. (2002) estimated 175 ± 10 km of offset geologic changes in the same time will be the range of processes considered, an exhaustive along the East Bay (Hayward-Calaveras) fault modest. Many events that are infrequent on bibliography is impractical, and only represen- systems, but that error estimate is based on pos- a human time scale, such as earthquakes and tative references are cited. sible alignment errors in the rock units being volcanic eruptions, become commonplace on A futurist approach can serve to correct some correlated, not on statistical analysis. The age of longer time scales, and events that have not common misconceptions. One common, fre- the rock unit is given as 11–13 Ma with no error occurred in recorded history, such as major quently unconscious misconception is that his- estimate. Combining the two pieces of data, we ice ages, large meteor impacts, giant pyro- tory is linear, progressing toward an inevitable can estimate an average slip rate of 13–17 mm/ clastic eruptions, or collapses of Hawaiian end point. We can fail to realize that geologic yr, but the authors note that both overall rates of shield volcanoes, become almost inevitable in features are a snapshot of processes that were movement and slip along individual faults are a million years. highly dynamic and changeable. Our inability to highly variable in time, with long periods of qui- see ourselves as part of a continuum of processes escence alternating with periods of rapid slip. Keywords: geologic time, process rates, that will continue into the future is also directly Clearly, only a qualitative description of rates is geomorphology, tectonics, environmental linked to our shortsightedness in managing our justifi ed for this fault system, and the same is geology. environment. Another misconception is that all true of virtually all the other processes described geologic changes are slow and imperceptible, in this paper. INTRODUCTION whereas many observable changes take place even on the scale of a human lifetime, and even The Human Factor The Earth Has a History is a video produced more signifi cant changes have occurred during by The Geological Society of America (Palmer, the span of recorded history. Human impacts already equal or surpass 1991) to acquaint nongeologists with the con- There are practical applications for long-term many natural processes. For example, human cepts of geologic or “deep” time. A less con- geological prediction. Most geohazard projec- earth-moving processes exceed natural erosion ventional way to visualize geologic time is to tions need to forecast only a few decades or in the volume of material moved (Hooke, 2000; peer into the future. Even short geologic time centuries into the future, but geological storage Wilkinson, 2005). Some authors argue that scales outrun our ability to project human his- of high-level nuclear waste requires estimates humans are now creating a mass extinction to tory, whereas many geologic processes will of geological stability on scales ranging up to a rival anything in the geologic record (Leakey and have barely begun to produce visible changes. million years (Sun, 2001). Lewin, 1996), and we are using many resources Events that are rare or unknown in recorded his- A million years is relatively short in geologic faster than they are created geologically. Global tory become almost inevitable, even frequent, in terms. For example, even the fastest plates, mov- heat fl ow, ~4.4 × 1013 W or 1.4 × 1021 J/yr (Pol- the near geologic future. This paper will explore ing on the order of 15 cm/yr, will have moved lack et al., 1993), is only about a factor of 3.5 the likely future of Earth on geologically short only 150 km in a million years, enough to have greater than human energy use (~4 × 1020 J/yr; time scales ranging from 1000 yr to 1 m.y. The very signifi cant local geological effects but U.S. Department of Energy, 2004). Attempting intent of this paper is to illustrate geologic time scarcely enough to be casually noticeable on a to forecast human activities on scales up to a mil- by peering into the future, not to make rigorous globe. It is unlikely that erosion will have greatly lion years is the height of speculation, but some predictions or speculate about human history. lowered any of Earth’s major mountain ranges discussion of the range of possible impacts is in My emphasis will be on changes in selected in that time. Given the relatively short spans order. We can consider three broad scenarios for systems that are statistically or cyclically pre- covered, we can reasonably extrapolate many future human environmental impact. dictable, and there will be no attempt to specu- geologic process rates. On the other hand, the Low impact. Human impact is below present late about unknown or unpredictable processes uncertainty of measurement, the range of rates levels. Humans may reform their most destruc- like changes in plate motion, nor any attempt to observed for processes, the inherent variability tive practices and remain within the limits of cover all possible changes. At each time scale of rates even within a single system, and the environmental sustainability. Less appealing I will examine selected geomorphic processes, likely infl uence of unpredictable perturbations scenarios are that humans may become extinct, Geosphere; May 2006; v. 2; no. 3; p. 113–124; doi: 10.1130/GES00012.1; 7 tables, 7 animations. For permission to copy, contact [email protected] 113 © 2006 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/2/3/113/3335090/i1553-040X-2-3-113.pdf by guest on 27 September 2021 S.I. DUTCH or technological civilization may collapse might derive our energy and mineral resources predicted by estimating future natural geologi- through war or natural disaster (such as a large from space rather than from Earth’s surface. cal changes with some component of present meteor impact). The longest time scales con- Medium impact. Human impact continues human effects superimposed, but it is impossible sidered here might allow several cycles of col- at a pace comparable to or somewhat greater to predict what forms extremely advanced tech- lapse and recovery. Human activities might also than present. Perhaps science and technology nology might assume, or what motivations and be spatially and temporally variable enough for will reach a plateau at a level not far beyond values humans with those powers might have. affected areas to recover naturally. Even within the present, or occasional reversals might cause A million years might be time for the human recorded history, major settlements have been technology to collapse or stagnate long enough species itself to evolve signifi cantly. Highly so thoroughly forgotten, overgrown, and buried for natural processes to keep pace with human advanced humans might have no need to disturb that only detailed excavation has brought them activity on millennium and longer time scales. the natural environment, or they may modify it to light. At the other technological extreme, High impact. In this scenario, the hardest to beyond recognition. technology might become so advanced that predict, human activity and technological capa- Any attempt to predict technology far in humans will no longer need to modify the natu- bility continue to grow toward some unfore- advance is bound to be almost pure specula- ral environment extensively. For example, we seeable level. Low and medium impact can be tion, so this paper will focus mostly on low and medium impact scenarios. The emphasis of this paper, after all, is to visualize geologic time by projecting what geologic processes are likely to do at their average rates, not an attempt to predict future human history. Even where humans are signifi cantly modifying natural geological pro- cesses (for example, preventing the diversion of the Mississippi River), it is questionable whether those changes will last for geologically signifi - cant times. For example, even if New Orleans still exists in 1000 yr, will there still be an eco- nomic need to maintain the present course of the Mississippi? Also, even if humans still have a reason to control the course of the Mississippi 1000 yr hence, the likelihood of a fl ood capable of overwhelming any control measures is quite high over such a long span (as was shown by Hurricane Katrina, which struck as this paper was being revised). Humans may not be able to prevent the diversion of the Mississippi on a long time scale even if they want to. Animation 1. Motion of the San Andreas Fault near San Francisco for the next million years, shown on progressively longer time scales and larger areal scales. The inclusion of IMPACT OF FUTURE CHANGES cultural features is solely to illustrate the scale and rate of fault motion, and does not imply any predictions of future seismic hazard.