Annual Review of Earth and Planetary Sciences - Current Issue
Volume 52, 2024
-
-
Evolution, Modification, and Deformation of Continental Lithosphere: Insights from the Eastern Margin of North America
Vol. 52 (2024), pp. 549–580More LessContinental lithosphere is deformed, destroyed, or otherwise modified in several ways. Processes that modify the lithosphere include subduction, terrane accretion, orogenesis, rifting, volcanism/magmatism, lithospheric loss or delamination, small-scale or edge-driven convection, and plume-lithosphere interaction. The eastern North American margin (ENAM) provides an exceptional locale to study this broad suite of processes, having undergone multiple complete Wilson cycles of supercontinent formation and dispersal, along with ∼200 Ma of postrift evolution. Moreover, recent data collection efforts associated with EarthScope, GeoPRISMS, and related projects have led to a wealth of new observations in eastern North America. Here I highlight recent advances in our understanding of the structure of the continental lithosphere beneath eastern North America and the processes that have modified it through geologic time, with a focus on recent geophysical imaging that has illuminated the lithosphere in unprecedented detail.
- ▪ Eastern North America experienced a range of processes that deform, destroy, or modify continental lithosphere, providing new insights into how lithosphere evolves through time.
- ▪ Subduction and terrane accretion, continental rifting, and postrift evolution have all played a role in shaping lithospheric structure beneath eastern North America.
- ▪ Relict structures from past tectonic events are well-preserved in ENAM lithosphere; however, lithospheric modification that postdates the breakup of Pangea has also been significant.
-
-
-
Cenozoic History of the Indonesian Gateway
Vol. 52 (2024), pp. 581–604More LessThe tectonically complex Indonesian Gateway is part of the global thermohaline circulation and exerts a major control on climate. Waters from the Pacific flow through the Indonesian Archipelago into the Indian Ocean via the Indonesian Throughflow. Much progress has been made toward understanding the near-modern history of the Indonesian Gateway. However, the longer-term climate and ocean consequences of Australia's progressive collision with the Eurasian Plate that created it are less known. The gateway initiated ∼23 Ma, when Australia collided with Southeast Asia. By ∼10 Ma the gateway was sufficiently restricted to create a proto–warm pool. During the Pliocene it alternated between more or less restricted conditions, until modern oceanic conditions were established by 2.7 Ma. Despite its tectonic complexity, climate modeling and Indian and Pacific scientific ocean drilling research continue to yield insights into the gateway's deep history.
- ▪ The Indonesian Gateway is a key branch of global thermohaline oceanic circulation, exerting a major control on Earth's climate over the last 25 Myr.
- ▪ We find that a complex interplay of tectonics and sea level has controlled Indonesian Gateway restriction since 12 Myr, resulting in La Niña– and El Niño–like states in the equatorial Pacific.
- ▪ Long term Indonesian Gateway history is best determined from ocean drilling cores on the Indian and Pacific sides of the Indonesian Gateway, as records from within it are typically disrupted by tectonics.
- ▪ Model simulations show the global impact of the Indonesian Gateway. Further modeling with ocean drilling/tectonic research will enhance our understanding of Cenozoic Indonesian Gateway history.
-
-
-
The Composition of Earth's Lower Mantle
Vol. 52 (2024), pp. 605–638More LessDetermining the composition of Earth's lower mantle, which constitutes almost half of its total volume, has been a central goal in the Earth sciences for more than a century given the constraints it places on Earth's origin and evolution. However, whether the major element chemistry of the lower mantle, in the form of, e.g., Mg/Si ratio, is similar to or different from the upper mantle remains debated. Here we use a multidisciplinary approach to address the question of the composition of Earth's lower mantle and, in turn, that of bulk silicate Earth (crust and mantle) by considering the evidence provided by geochemistry, geophysics, mineral physics, and geodynamics. Geochemical and geodynamical evidence largely agrees, indicating a lower-mantle molar Mg/Si of ≥1.12 (≥1.15 for bulk silicate Earth), consistent with the rock record and accumulating evidence for whole-mantle stirring. However, mineral physics–informed profiles of seismic properties, based on a lower mantle made of bridgmanite and ferropericlase, point to Mg/Si ∼ 0.9–1.0 when compared with radial seismic reference models. This highlights the importance of considering the presence of additional minerals (e.g., calcium-perovskite and stishovite) and possibly suggests a lower mantle varying compositionally with depth. In closing, we discuss how we can improve our understanding of lower-mantle and bulk silicate Earth composition, including its impact on the light element budget of the core.
- ▪ The chemical composition of Earth's lower mantle is indispensable for understanding its origin and evolution.
- ▪ Earth's lower-mantle composition is reviewed from an integrated mineral physics, geophysical, geochemical, and geodynamical perspective.
- ▪ A lower-mantle molar Mg/Si of ≥1.12 is favored but not unique.
- ▪ New experiments investigating compositional effects of bridgmanite and ferropericlase elasticity are needed to further our insight.
-
-
-
The Geologic History of Plants and Climate in India
Vol. 52 (2024), pp. 639–661More LessIndia's diverse vegetation and landscapes provide an opportunity to understand the responses of vegetation to climate change. By examining pollen and fossil records along with carbon isotopes of organic matter and leaf wax, this review uncovers the rich vegetational history of India. Notably, during the late Miocene (8 to 6 Ma), the transition from C3 to C4 plants in lowland regions was a pivotal ecological shift, with fluctuations in their abundance during the late Quaternary (100 ka to the present). In India, the global phenomenon of C4 expansion was driven by the combined feedback of climate variations, changes in substrate conditions, and habitat disturbances. The Himalayan region has experienced profound transformations, including tree-line migrations, shifts in flowering and fruiting times, species loss, and shifts in plant communities due to changing monsoons and westerlies. Coastal areas, characterized by mangroves, have been dynamically influenced by changing sea extents driven by climate changes. In arid desert regions, the interplay between summer and westerlies rainfall has shaped vegetation composition. This review explores vegetation and climate history since 14 Ma and emphasizes the need for more isotope data from contemporary plants, precise sediment dating, and a better understanding of fire's role in shaping vegetation.
- ▪ This review highlights diverse vegetation and landscapes of India as a valuable source for understanding the vegetation-climate link during the last 14 Myr.
- ▪ A significant ecological shift occurred during 8 to 6 Ma in India, marked by the transition from C3 to C4 plants in the lowland regions.
- ▪ The abundance of C3 and C4 plants varied in India during the late Quaternary (100 ka to present).
- ▪ This review emphasizes the importance of more isotope data, precise sediment dating, and a better understanding of fire's role in shaping vegetation.
-
-
-
Grain Size in Landscapes
Vol. 52 (2024), pp. 663–692More LessEarth's terrestrial topography evolves in response to the interaction of tectonics, climate, and lithology. Recent discoveries suggest that the grain size of sediments produced on hillslopes and transported through river networks is key to understanding these interactions. Hillslope grain size varies systematically with erosion rate and residence time, the degree of chemical and physical weathering, and the fracture density and susceptibility to weathering of rock. Variations in initial grain size strongly influence the spatial evolution of grain size distributions as particles mix and wear during downstream transport through channel networks. In rivers, the size and flux of the coarse fraction of the sediment load control the rate of incision into bedrock and thus govern channel slope and ultimately the relief of actively eroding landscapes. These relationships suggest that a primary way that tectonics, climate, and lithology influence landscape evolution is through their controls on sediment grain size.
- ▪ Recent research reveals the central role of sediment grain size in controlling bedrock river morphodynamics, linking grain size to channel slope and topographic relief.
- ▪ Tectonics, climate, and lithology govern the size of sediments produced on hillslopes; hence, grain size mediates their influence on landscape evolution.
- ▪ Feedbacks linking sediment grain size, topography, weathering, erosion, and sediment transport provide new opportunities for advances in Earth surface science.
-
Previous Volumes
-
Volume 52 (2024)
-
Volume 51 (2023)
-
Volume 50 (2022)
-
Volume 49 (2021)
-
Volume 48 (2020)
-
Volume 47 (2019)
-
Volume 46 (2018)
-
Volume 45 (2017)
-
Volume 44 (2016)
-
Volume 43 (2015)
-
Volume 42 (2014)
-
Volume 41 (2013)
-
Volume 40 (2012)
-
Volume 39 (2011)
-
Volume 38 (2010)
-
Volume 37 (2009)
-
Volume 36 (2008)
-
Volume 35 (2007)
-
Volume 34 (2006)
-
Volume 33 (2005)
-
Volume 32 (2004)
-
Volume 31 (2003)
-
Volume 30 (2002)
-
Volume 29 (2001)
-
Volume 28 (2000)
-
Volume 27 (1999)
-
Volume 26 (1998)
-
Volume 25 (1997)
-
Volume 24 (1996)
-
Volume 23 (1995)
-
Volume 22 (1994)
-
Volume 21 (1993)
-
Volume 20 (1992)
-
Volume 19 (1991)
-
Volume 18 (1990)
-
Volume 17 (1989)
-
Volume 16 (1988)
-
Volume 15 (1987)
-
Volume 14 (1986)
-
Volume 13 (1985)
-
Volume 12 (1984)
-
Volume 11 (1983)
-
Volume 10 (1982)
-
Volume 9 (1981)
-
Volume 8 (1980)
-
Volume 7 (1979)
-
Volume 6 (1978)
-
Volume 5 (1977)
-
Volume 4 (1976)
-
Volume 3 (1975)
-
Volume 2 (1974)
-
Volume 1 (1973)
-
Volume 0 (1932)