igneous crust, and sediments until their eventual expulsion into the water column or atmosphere, however, is in its infancy. We need to better understand the physical properties of the medium through which the fluids flow, the stresses acting on the systems, and their chemical, mechanical, and thermal interaction with their host rock.

• The recognition that present-day conditions may not be representative of the whole of geologic history. A glance at the recent past shows a climate system principally forced by the eccentricity of Earth's orbit. Present-day nearshore sedimentary sequences reflect flooding of the world's shelves following the melting of large continental ice sheets, and today's seafloor volcanic activity is completely dominated by steady-state formation of new crust at the mid-ocean ridge. However, with the benefit of the geologic record, we see that just one million years ago variations in Earth's tilt were more important than eccentricity in modulating climate. During glacial maxima, sediments bypassed many continental margins through a series of canyons. In the Cretaceous, plume-type volcanism was far more important than it is today in the mass and energy transfer between the deep Earth and the surface. While in some cases, the causes of the changes in the geologic record are easily identified (e.g., rising sea level), in other cases they are not. More emphasis in the future will be directed toward documenting the various different stable states of Earth's systems, discovering what events trigger evolution from one stable state to another, and identifying the linkages between the states of very different systems (e.g., climate and tectonics).

• The importance of explicit incorporation of effects of and on the biosphere into marine geology and geophysics. Investigators in MG&G are extremely comfortable with introducing a fair amount of physical and chemical sophistication in their science. Many have their primary professional training in these allied physical sciences. The links to biology, in comparison, are weaker and must be shored up to make progress on a number of fronts. Just as ocean chemistry cannot be understood using the principles of chemical equilibrium without taking into account biochemical cycling of nutrients, the solid Earth is modified by biologic activity from the scale of bacteria to humans. Submarine ecosystems harbor some of the most unusual and extreme examples of life on Earth, and the implications of understanding how these systems have adapted to and how they modify their environments have implications for the origin of life itself.

• The appreciation that we must move beyond steady-state models to study geologic events as they happen. The geologic record contains evidence of many catastrophic events: earthquakes, landslides, volcanic eruptions, etc. Most of our models, however, smooth these events over time to create steady-state representations for what are really discontinuous processes such as erosion of headlands, glacial meltwater pulses, creation of oceanic crust, and filling of flexural moats. Such steady-state models distort the true impact of these events on human timescales and are useless for any hazard mitigation. Given the current lack of understanding of the temporal and spatial pattern of most geologic events, we require the technology to install undersea observatories and event-detection systems to catch geologic events in action.

• The limitations of present funding structures and technology for problems that span the shoreline. From the standpoint of many problems in geology and geophysics, the division between the Ocean Science and Earth Science divisions at NSF is somewhat artificial. Although most of the mid-ocean ridge system is under water, sometimes it is easiest to map it where it lies above sea level (e.g., Iceland). Fluids vented along coastal margins may originate from terrestrial aquifers. Variations in sea level shift the shoreline position laterally for distances of kilometers over timescales of millennia. Ice core data from subaerial drilling can complement deep sea cores. Most efficient use of future resources will require close collaborations between land and marine geoscientists and their corresponding program officers. Even more of an impediment to working across the shoreline is lack of equipment to work near the shoreline, in shallow-water, high-energy environments. No amount of community interest in geologic processes at the oceanic margins will lead to progress unless improved technology is available for imaging, sampling, and monitoring the near-shore region.

Overall, the thematic reports, briefly summarized below, give the impression of anything but "business as usual." The community is enthusiastic about the opportunities to build new collaborations and apply new technology and expertise to find answers to the most intellectually challenging problems in marine geology and geophysics.

The solid Earth is continually in movement, and this movement reflects the processes of energy and mass exchange between the Earth's interior and exterior reservoirs. The current manifestations of these movements are represented by the diverse plate tectonic settings of the Earth, many of which are depicted schematically in Figure 1. This snapshot of the plate tectonic physical and geochemical circulation can also be considered conceptually as a cycle, as shown in Figure 2. The cycle begins with the formation of a new rift, followed by the opening of an ocean basin as new oceanic plate is created by spreading at ocean ridges. The aging oceanic plate is acted on by a variety of mid-plate processes such as hotspots (including seamount and island volcanism), sedimentation, subsidence, and deformation. As the plate approaches a convergent margin, it enters the "subduction factory," leading to the generation of earthquakes, release of fluids, varieties of volcanism, back-arc spreading, and ultimate recycling of residual peridotite, basalt, and sedi