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A Depth CSF (m)
0 10 20 30 40 50
600 1
Magnetic susceptibility (10 -6 SI) 400 1 2 2 3 3 4 4 5 5 6 Figure 2. The tops and bottoms of cores are usually disturbed and

there are often coring gaps between cores. To remedy this and cre-
ate a complete stratigraphic sequence, a “composite” ideal core is
created by splicing together data from different holes to so that
200
coring gaps in one hole are filled with core intervals from an adja-
erate a composite core depth below seafloor (CCSF-A) at least two
0 1 2 3 4 5 cent hole, trying not to use the tops and bottoms of cores. To gen-
or more holes are drilled at each site and each hole is slightly offset
by depth from the other (Fig. S3 [see text footnote 1]). Hole core
Depth CCSF-A (m) measurements, such as magnetic susceptibility and natural
B 0 10 20 30 40 50 gamma ray, and/or split core images and lithologic changes from
the different holes are aligned using distinguishing features, such
600 1 as a sharp peak or a color change. (See Figs. S3–S5 for additional
Magnetic susceptibility (10 -6 SI) 400 1 2 2 3 3 4 4 5 5 6 measurements from different holes are aligned by depth; Hole
examples.) (A) Example from Site U1333, central Pacific, showing
construction of a CCSF-A. In this example, magnetic susceptibility
U1333A (red), Hole U1333B (blue), Hole U1333C (green). Numbers
indicate the order of cores taken in the hole. (B) Depth-shifted
cores on composite depth scale (CCSF-A [m]) aligning distinguish-
200
ing features. (C) The magnetic susceptibility records the different
the bottom. Along the top, core breaks (triangles) and hole desig-
0 1 2 3 4 5 holes that are part of the splice are shown by the hole color along
nations are shown (from Pälike et al., 2010).
C Depth CCSF-A (m)
0 B A 10 B C 20 B C 30 B C 40 B C 50 Revolution #1: Plate Tectonics
Magnetic susceptibility (10 -6 SI) 400 has come from geophysical studies,
600
In the ocean, plate tectonic knowledge
200
submersible observations, and samples,
drill cores, and instrumented boreholes to
0
monitor in situ processes. As information
leading to the wide acceptance of plate
inaccessible. Without a riser system, with integrated approach is laid out in the pres- tectonics accumulated, one of the most
its casing and the ability to circulate mud ent science plan: Illuminating Earth’s Past, convincing data sets came from DSDP
and prevent blowouts, many thickly sedi- Present, and Future (IODP, 2011). Leg 3. “The most interesting finding from
mented continental margins and subduc- the paleontological studies is the correla-
tion zones were out of reach. Locations at SOME SOD HIGHLIGHTS tion of paleontologic ages of sediments
some high latitudes with ice and in very SOD has been an engine for understand- immediately overlying the basalt base-
shallow water could not be explored. To ing Earth processes. Tens of thousands of ment with ages of basement predicted by
meet these scientific needs, a new era of papers have been published, some among the sea-floor spreading hypothesis”
SOD began in October 2003. The riser- the most highly cited in Earth science. (Maxwell et al., 1970, p. 445).
equipped, Japanese-built Chikyu, capable Thousands of scientists from around the Below, briefly summarized, are some
of drilling deep into heavily sedimented world, from undergraduates to emeritus, of the major results learned since Leg 3.
margins, and the mission-specific drilling have been involved in the research, form-
platforms (MSPs) operated though the ing international collaborations extending Rifted Margins (Also Called Passive
European Consortium for Ocean Research beyond SOD. Margins)
Drilling were added. Describing the results in a short paper is Continental rifting and ocean basin
challenging and necessarily incomplete. formation are central processes of plate
International Ocean Discovery Program Here, three areas where SOD contributed tectonics and continue to be an important
(IODP, 2013–2023) to major revolutions in our understanding focus of SOD. This is an iterative process,
Today, there is a much broader under- of Earth are described: plate tectonics, with geophysical surveys identifying
standing of the interconnections among paleoceanography, and the deep marine prime drilling targets and SOD providing
Earth’s spheres, and new fields of research biosphere. These topics are intertwined. the cores to determine the age and compo-
have developed. Much has been learned Clearly, plate tectonics impacts ocean and sition of specific reflectors. Primary influ-
about how Earth operates. But, the details climate history, which in turn affects the ences on rift development are related to
necessary to reach the next level of under- deep biosphere; all are connected through mantle composition, thermal structure, and
standing require interdisciplinary exper- carbon and water cycling. Future drilling tectonic stresses. This results in two end-
tise, atmospheric scientists, computer will continue to enhance geoscientists’ member classifications, magma-rich and
modelers, and biologists. Achieving deeper understanding of interconnected Earth magma-poor (non-volcanic) margins.
knowledge has become more complex and processes from both a planetary and a Magma-rich margins were drilled dur-
requires a new approach. This broadly human impact perspective. ing multiple expeditions (Legs 38, 81, 104,

6 GSA Today | March-April 2019