Annual Review of Earth and Planetary Sciences - Volume 45, 2017

Current end-member models for the geodynamic evolution of orogenic plateaus predict (a) slow and steady rise during crustal shortening and ablative subduction (i.e., continuous removal) of the lower lithosphere or (b) rapid surface uplift following shortening, which is associated with punctuated removal of dense lower lithosphere and/or lower crustal flow. This review integrates results from recent studies of the modern lithospheric structure, geologic evolution, and surface uplift history of the Central Andean Plateau to evaluate the geodynamic processes involved in forming it. Comparison of the timing, magnitude, and distribution of shortening and surface uplift, in combination with other geologic evidence, highlights the pulsed nature of plateau growth. We discuss specific regions and time periods that show evidence for end-member geodynamic processes, including middle–late Miocene surface uplift of the southern Eastern Cordillera and Altiplano associated with shortening and ablative subduction, latest Oligocene–early Miocene and late Miocene–early Pliocene punctuated removal of dense lower lithosphere in the Eastern Cordillera and Altiplano, and late Miocene–early Pliocene crustal flow in the central and northern Altiplano.

Earth's climate affects nearly all aspects of landscape evolution, from the breakdown of rock to the delivery of sediment to the oceans. Yet quantifying climate's influence on landscapes is a major challenge, not only because it is difficult to know how landscapes responded to past changes in climate, but also because landscapes are shaped by various processes that respond to climate in different ways. I review the current state of efforts to quantify climate's effects on the rates of the main processes that drive landscape evolution, with a focus on unglaciated landscapes formed by bedrock erosion. Although many uncertainties remain, recent research has clarified how the processes governing hillslopes, bedrock channels, and chemical erosion depend on major climate factors such as precipitation and temperature. A few themes emerge, including the importance of climatically mediated biological processes, the role of variability, and the value of natural experiments for revealing climate's effects.

The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—which are marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included not only the development of uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental control over the distribution of taxa in time and space.

Heavily cratered surfaces on the Moon, Mars, and Mercury show that the terrestrial planets were battered by an intense bombardment during their first billion years or more, but the timing, sources, and dynamical implications of these impacts are controversial. The Late Heavy Bombardment refers to impact events that occurred after stabilization of the planetary lithospheres such that they could be preserved as craters and basins. Lunar melt rocks and meteorite shock ages point toward a discrete episode of elevated impact flux between ∼3.5 and ∼4.0–4.2 Ga, and a relative quiescence between ∼4.0–4.2 and ∼4.4 Ga. Evidence from Precambrian impact spherule layers suggests that a long-lived tail of terrestrial impactors lasted to ∼2.0–2.5 Ga. Dynamical models that include populations residual from primary accretion and destabilized by giant planet migration can potentially account for the available observations, although all have pros and cons. The most parsimonious solution to match constraints is a hybrid model with discrete early, post-accretion and later, planetary instability–driven populations of impactors.

Glaciers offer the potential to reconstruct past climate over timescales from decades to millennia. They are found on nearly every continent, and at the Last Glacial Maximum, glaciers were larger in all regions on Earth. The physics of glacier-climate interaction are relatively well understood, and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent. This can lead to significant insights regarding past, present, and future climate. For example, glacier modeling has demonstrated that the near-ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global-scale climate warming of ∼1°C, consistent with instrumental data and climate proxy records. Climate reconstructions from glaciers have also demonstrated that the tropics were colder at the Last Glacial Maximum than was originally inferred from sea surface temperature reconstructions. Future efforts to reconstruct climate from glaciers may provide new constraints on climate sensitivity to CO2 forcing, polar amplification of climate change, and more.

Internally generated, or autogenic, terrestrial and marine sediment-transport dynamics can produce depositional patterns similar to those associated with climatic, tectonic, or sea level changes. A central challenge in accurately interpreting the sedimentary archive is determining what scales and types of deposits reflect autogenic controls on sedimentation in different environments. Autogenic sediment-transport dynamics commonly result from intermittent sediment storage in transient landforms, which produces episodic, spatially discontinuous sedimentation across a basin. The transition from localized, variable sedimentation to even, basin-wide sedimentation marks the shift from stochastic landscape dynamics to deterministic deposition responding to the long-term balance between sediment supply and the creation of space to accommodate sediment. This threshold can be measured in a wide variety of stratigraphic successions and has important bearing on whether climatic, tectonic, or sea level signals can be recognized in physical sedimentary deposits.