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Overview
Structure
CIDER development timeline
Upcoming Meetings
- 2012 Summer Program
Past Meetings
- 2011 Post-AGU Workshop
- 2011 Summer Program
- 2011 Imaging Workshop
- 2010 Summer Program
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2010 SEDI conference
- 2009 Workshop at Marconi Center
- 2008 Summer Program
- 2006 Summer Program
- 2004 Summer Program
- 2003 Workshop
CIDER Bibliography in progress
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Agenda & Video, Logistics, Participants, Travel Reimbursements, Announcements
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Science motivation for 2012 CIDER Summer Program
Many processes key to the birth of the modern Earth occurred early in our planet's history. The violent events of accretion determined the composition of the planet as well as its initial thermal state. The conditions of core formation determined its composition and consequently the dynamics of thermo-chemical convection in the modern outer core. Giant impacts profoundly altered Earth's chemical and physical state and created the Moon. Convection in the early mantle led eventually to plate tectonics. Widespread melting of the planet created Earth's earliest crust and was accompanied by massive degassing that lead eventually to Earth's unique atmosphere and equable climate.
The last 10 years have seen an explosion of new data and new models pertaining to the early Earth, catalyzed by advances in disciplines ranging from geophysics, geochemistry, planetary and atmospheric sciences, to geobiology. The aim of the 2012 CIDER Summer Program is to foster communication between disciplines to address key questions about the early Earth.
The composition, energetics, and earliest differentiation of the Earth are intimately linked with the process of accretion and the history of large to giant impacts on the growing protoplanet. Improvements in modeling have provided a wealth of data on accretion and impact processes, including the time scales of planetary accretion, the delivery of volatiles to Earth from the outer solar system, and the consequences of a giant impact on the formation of the Moon, the creation of a magma ocean and the retention of H2O and other volatiles.
Recent developments in geochemistry yield spectacular glimpses of the early Earth. Evidence from 142Nd isotopes seem to require either that the Earth accreted from materials distinct from chondritic meteorites or that there is a considerable hidden geochemical reservoir deep in the Earth that has persisted for >4 Ga. One possibility calls into question standard models for terrestrial accretion and the other suggests that early differentiation continues to influence the structure and dynamics of Earth's mantle. Both challenge long-standing assumptions about the composition of the Earth. Combination of short-lived chronometers such as 182Hf/182W with more conventional isotopic systems sheds light on the timing of planetary accretion and its earliest differentiation, including core formation and the birth of the Moon.
A key chapter in early Earth evolution is formation and crystallization of a vast magma ocean (or oceans?) in which most or all of the mantle was melted owing to heat produced by accretion, giant impacts, early radionuclides, and the gravitational potential energy liberated from segregation of the metallic core. Magma ocean solidification may have lead to density stratification of the resulting crystalline mantle, which in turn would have affected the style of early convection.
Improved seismic imaging of the deepest parts of the mantle reveals complex structures that may have formed in the first billion years. The bottommost ~200 km of the mantle, known as the D" layer, seems to have a distinct composition that may have survived ~4 Ga of mantle convection, and this may corroborate evidence from 142Nd. Further, D" includes regions of partial melt at the core mantle boundary that may be remnants of a primordial magma ocean. Advances in mineral physics have begun to reveal that this region may be composed of materials with novel properties, in part owing to changes occurring in the perovskite phase at the temperature and pressure conditions of the lowermist mantle (i.e. the "post-perovskite" phase), in part owing to a change in spin state of iron at depth. Further development of isotopic and geophysical probes, as well as mineral physics and geodynamical studies are required to fully comprehend how the legacy of early Earth is expressed in the deepest parts of the mantle, and determine how mantle dynamics made the transition from its early regime to plate tectonics.
Magma oceans also allowed profound degassing of the solid Earth, and likely created an early atmosphere hundreds of times thicker than that of the present day. This early atmosphere was also affected by mass losses to space. Debate continues as to the composition of this early atmosphere and how it changed through time, its relation to climactic evolution, to formation and stabilization of the oceans, and its relationship to prebiotic chemistry.
Another key aspect of Deep Time is the thermal evolution of the planet. Differentiation of the early Earth combined with self-compression created a dense metallic core that stores much Earth's thermal energy. Gradual release of this energy through crystallization of the inner core, is key to the origin and maintenance of the geodynamo. We do not know when in Earth history the geodynamo began or when the inner core was born. Further investigations of the magnetization of ancient rocks and minerals and modeling of core dynamics and the early magnetic field are needed. In addition, the secular cooling of Earth's interior has influenced the core, as the origin of the inner core and the powering of the geodynamo are intimately related to the history of heat fluxes across the core-mantle boundary. To understand Earth's thermal history, we can look at everything from the history of Earth's magnetic field, as it may record the thermal evolution of the core, to temperature dependences of the physical and chemical properties of mantle materials, to the compositions of mantle and volcanic rocks.
Finally, there is the question of the earliest formation of continental crust and lithosphere. Continental cratons preserve rocks as old as 4 Ga or perhaps older, but recent discoveries from zircons – zirconium silicate accessory minerals that function as unique time capsules –from the Jack Hills of western Australia demonstrate that differentiated rocks not too different from modern continental crust was forming as early as 4.4 Ga. Moreover, these same zircons demonstrate that liquid oceans were present and that surface recycling processes similar to plate tectonics or formation of significant thicknesses of lithosphere were occurring almost from the outset of Earth history. The wealth of data from the Jack Hills presents strong challenges to our understanding of early geodynamics and early evolution of Earth's hydrosphere and climate. On the other hand, recent seismic investigations of the oldest parts of continents, i.e. the Archean "cratons" indicate that the top part of the lithosphere may be chemically distinct and may have formed under a different convective regime than the deeper parts, which can be explained more readily by processes resembling current ocean floor creation and subduction.
The quest for understanding the impact of Deep Time on the modern Earth requires a multi-disciplinary effort, at the intersection of geochemistry, seismology, mineral physics, geodynamics, atmospheric science and geobiology. Deep Time is a timely and relevant subject for a multi-disciplinary CIDER summer program.
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For inquiries and practical questions, contact Micaelee Ellswythe (micaele AT berkeley DOT edu).
For questions on the scientific program, contact Marc Hirschmann, (mmh AT umn DOT edu) or Barbara Romanowicz, (barbara AT seismo DOT berkeley DOT edu).
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