Page 9 - i1052-5173-29-3-4

discovery of the hydrothermal vent com- connections between Earth’s spheres in to a changing environment. This informa-
munities a decade earlier. Yet these com- ways that will help to further revolutionize tion will increase understanding of biodi-
munities, invisible to the naked eye, con- geoscience. Each theme is briefly described versity and evolutionary paths on Earth
tain abundant biomass. Just how much is a in the following sections. and aid expectations for the existence of
matter of debate; Kallmeyer et al. (2012) life in other parts of the solar system.
estimated there are roughly as many cells Planetary Dynamics (Deep Processes
in marine sediment as in the ocean or in and Their Impact on the Earth’s Earth in Motion (Geohazards)
soil. Bar-On et al. (2018) refined the esti- Surface Environment) An increasing human population, espe-
mate to 77 Gt of carbon (~14% of biomass Plate tectonics is the driving force for cially in coastal areas, puts more people in
carbon) that reside in the deep subsurface, Earth processes. Yet, despite decades of harm’s way. This harm can come rapidly
both land and marine. research, some of the most basic mecha- from earthquakes, tsunamis, volcanoes,
Are they living cells? Metabolic rates of nisms are not fully understood. What is and landslides. This is an area where bore-
these communities are orders of magnitude clear is that the seemingly different com- hole tools have a crucial role in furthering
slower than those on the surface and hence ponents of the Earth system are connected, our understanding of the subsurface pro-
barely detectable (e.g., D’Hondt et al., 2002; and water and carbon are primary connec- cesses that cause these changes. Long-
Hoehler and Jørgensen, 2013). Unknown tors. To understand these processes, geo- term, in situ data collection can monitor
and critical to this discussion is determin- scientists need samples from the surface the conditions of earthquake generation
ing the connections between the geobio- sediment, through the ocean crust to the and biogeochemical cycling, allowing the
sphere that humans inhabit and this barely mantle. Although plate tectonics appears rate of the different components of these
explored marine world. to be a fairly steady-state process today, it changes to be better understood and pro-
The accomplishments that have been may not always have been so. For example, viding the data for more accurate modeling
made did not come easily. Even after there is much to learn about the past of these critical environments.
samples are collected, there are challenges, emplacement of large igneous provinces,
such as characterizing bacteria that grow so when massive amounts of mafic magma FUTURE (POST-2023)
slowly as to be virtually dormant. Despite were discharged into the ocean and onto Plans for the science program for the
the challenges, there is now access to this land, and abundant gases (CO 2, H 2S, and next phase of SOD are already under way
new world (Inagaki et al., 2015). Maybe SO 2) were emitted into the atmosphere. as many critical questions remain. For
fifty years from now geoscientists will be example: How do subduction zones initi-
shocked at our ignorance about such a Climate and Ocean Change: Reading ate and continents rift? How fast can sea
critical component of Earth processes. the Past, Informing the Future level rise? How have marine microbial
Gas hydrates are also part of deep bio- The ocean ecosystem is changing in communities responded to past changes
sphere research. Several decades ago, they response to elevated atmospheric CO 2: in ocean chemistry and temperature? This
were inferred from bottom simulating it is becoming warmer, and the ocean is is an opportunity for geoscientists from
reflectors (BSRs), a puzzling reflector that acidifying. The rate of modern changes many disciplines and countries to become
corresponded with the predicted base of may be unprecedented (except for asteroid involved in the continuation of an exciting
the methane hydrate stability zone. First impacts), but Earth has experienced simi- international program that is critical to
cored on Leg 67, sediment above the BSR lar perturbations in the past. The carbon- Earth science.
indeed contained hydrates, and as the cores ate compensation depth has risen and
warmed and the gas expanded, the sedi- fallen, and icebergs left rocky trails of CONCLUSIONS
ment left the core barrel and shot across their passage. Through examination of Although we have yet to drill through
the deck. Special pressure core barrels marine sediment cores, geoscientists can the Mohorovicic Discontinuity, SOD has
needed to be and were developed. Now determine how the ocean (and ocean life) radically changed and continues to change
scientists on the JOIDES Resolution have responded in the past. Collecting the our view of Earth. Early SOD showed an
cored gas hydrates in many environments, detailed data necessary to better charac- unexpectedly young ocean and confirmed
especially on subduction margins. For terize past changes will help climate mod- plate tectonics as the underlying mecha-
example, scientists on Expedition 311 elers better predict our future. nism for Earth processes. Recent SOD
(Cascadia Margin) determined that most of provides new information about elemental
the marine hydrate is caused by the micro- Biosphere Frontiers: Deep Life, recycling and Earth history. Just as we
bial reduction of CO 2 within the hydrate Biodiversity, and Environmental learn more about outer space and the ori-
stability zone (Riedel et al., 2010). Looking Forcing of Ecosystems gin of the universe with better telescopes
to the future, dissociation of hydrates The unexpected finding of microbial and planetary missions, we will learn more
might produce slope instability and the communities in the sea floor opens a wide about our planet, the processes that drive
release of methane. variety of possibilities for exploration. it, and the origin of life as drilling technol-
Their very existence challenges our under- ogy improves. The intrigue continues as
PRESENT (2013–2023) standing of the minimal conditions neces- each seismic survey defines where to drill,
Illuminating Earth’s Past, Present and sary for life. Three major themes are being each core sheds new light on Earth’s past
Future (IODP, 2011) describes four themes addressed: (1) sub-seafloor microbial com- and helps predict its future, and borehole
of focus for the current IODP. It highlights munities; (2) the limits to life in the deep instrumentation provides in situ monitor-
opportunities to use SOD to explore biosphere; and (3) community adaptation ing of Earth’s processes.

www.geosociety.org/gsatoday 9