Norman H Sleep

Stanford University | SU · Department of Geophysics

The Paleocene‐Eocene Thermal Maximum (PETM) and the lower Chron 29n hyperthermal event were recently proposed to have been triggered by the meteorite impacts that formed the Marquez Dome (Texas, USA; 58.3 ± 3.1 Ma) and Boltysh (Ukraine; 65.39 ± 0.14 Ma) craters, respectively. We use shock physics hydrocode simulations and radiative forcing calculat...

As Mars transitioned from an early Earth-like state to the cold desert planet it is today, it preserved a near pristine record of surface environments in a world without plate tectonics and complex life. The records of Mars’ Earth-like surfaces have remained largely untouched for billions of years, enabling space exploration to provide critical ins...

We provide an overview of a 2019 workshop on the use of fragile geologic features (FGFs) to evaluate seismic hazard models. FGFs have been scarcely utilized in the evaluation of seismic hazard models, despite nearly 30 yr having passed since the first recognition of their potential value. Recently, several studies have begun to focus on the impleme...

Strong seismic waves from the July 2019 Ridgecrest, California, earthquakes displaced rocks in proximity to the M 7.1 mainshock fault trace at several locations. In this report, we document large boulders that were displaced at the Wagon Wheel Staging Area (WWSA), approximately 4.5 km southeast of the southern terminus of the large M 6.4 foreshock...

The near‐field velocity pulse of large strike‐slip earthquakes brings near‐fault stiff crystalline rock into failure. The uppermost ~2 km beneath Pump Station 10 (PS10) likely failed nonlinearly during the 2002 Denali earthquake. High‐frequency S waves traversed this region during and immediately after failure with only weak waves reaching the surf...

Slip during large crustal earthquakes continues for extended periods of time on spatially extensive fault planes. High‐frequency body waves from other parts of the fault system thus impinge on patches of the fault that are still actively sliding. Intuitively, the material within sliding fault planes does not rheologically distinguish between the lo...

Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear inelastic failure. We examine implications of nonlinear viscous flow, which may be appropriate for shallow muddy soil, and contrast them with those of Coulomb friction within a shallow reverberating uppermost layer with low‐seismic velocities. Waves refract i...

The icy shells of Enceladus and Europa consist from top down of cold (~100 K) ice at low (<0.1 MPa) pressure, cold ice at high pressure up to ~10 MPa, and warm ice near 273 K the base. The pressure ~10 MPa and temperature near 273 K of basal ice within Enceladus and Europa are similar to that within terrestrial glaciers that are known to have seism...

An international consensus policy to prevent the biological cross-contamination of planetary bodies exists and is maintained by the Committee on Space Research (COSPAR) of the International Council for Science, which is consultative to the United Nations Committee on the Peaceful Uses of Outer Space. Currently, COSPAR’s planetary protection policy...

Real contacts on the scale of ~10 μm support gigapascal shear tractions and normal tractions on rapidly sliding faults. At sliding velocities above ~0.1 m/s, the asperity tips of the contacts become hot and weak. The macroscopic friction depends on the average strength of the asperity tips during their lifetimes of contact. The strength of the aspe...

The traditional tree of life from molecular biology with last universal common ancestor (LUCA) branching into bacteria and archaea (though fuzzy) is likely formally valid enough to be a basis for discussion of geological processes on the early Earth. Biologists infer likely properties of nodal organisms within the tree and, hence, the environment t...

Seafloor and passive margins gradually subside as a result of thermal contraction of the underlying lithosphere. Thermal subsidence is also an attractive mechanism for the Michigan basin. For subsidence to occur within this previously stable continental region, some mechanism is needed to heat the lithosphere and to reduce the buoyancy of the conti...

How can scientists conclude with high confidence that an exoplanet hosts life? As telescopes come on line over the next 20 years that can directly observe photons from terrestrial exoplanets, this question will dictate the activities of many scientists across many fields. The expected data will be sparse and with low signal-to-noise, which will mak...

A normal-fault offsets the Cretaceous-Paleogene boundary layer and lower units at the well-known Madrid and Long's Canyon outcrops near Trinidad, Colorado, but not the overlying units. Seismite structures are present at both sites. Strong seismic waves from the Chicxulub crater likely triggered an event on the exposed fault that has not slipped aga...

Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear anelastic failure. The construct of coulomb friction yields testable predictions about this process for strong‐motion records. Physically, the anelastic strain rate increases rapidly with increasing dynamic stress, and dynamic stress is proportional to the di...

Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on ∼35 km thick continental crust (DePaolo et al., 1983; Montanari et al., 1983; Hildebrand and Boynton, 1988, 1990). This evidence, along with ejected terrestrial chromites (Olds et al., 20...

Strong long-period (∼3 s) seismic waves impose dynamic strains on the shallow subsurface. The dynamic strain is the dynamic velocity divided by the phase velocity of thewaves. The dynamic stress is the strain times the shear modulus. A testable hypothesis is that the shear modulus of the rock self-organizes so that the rock barely fails in friction...

Strong Rayleigh waves are expected to bring the shallow subsurface into frictional failure. They may nonlinearly interact with high-frequency S waves. The widely applied Drucker and Prager (1952) rheology predicts that horizontal compression half-cycle of strong Rayleigh waves will increase the strength of the subsurface for S waves and predicts th...

Naturally occurring Cr(VI) has been ascribed to terrestrial Cr(III) oxidation by Mn (di)oxides, generated through reaction of Mn(II) with molecular oxygen (O 2). However, hydrogen peroxide (H 2 O 2) is a potential oxidant of Cr(III) that may form in serpentinization (high H 2 , low O 2) systems where chromite [i.e., the main mineralogical source of...

The silicate Earth contains Pt-group elements in roughly chondritic relative ratios, but with absolute concentrations <1% chondrite. This veneer implies addition of chondrite-like material with 0.3-0.7% mass of the Earth's mantle or an equivalent planet-wide thickness of 5-20 km. The veneer thickness, 200-300 m, within the lunar crust and mantle is...

The main San Andreas Fault strikes subparallel to compressional folds and thrust faults. Its fault-normal traction is on average a factor of γ=1+2μthr(1+μthr2+μthr), where μthr is the coefficient of friction for thrust faults, times the effective lithostatic pressure. A useful upper limit for μthr of 0.6 (where γ is 3.12) is obtained from the lack...

Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt,...

Numerical calculations assuming linear elasticity by Böse et al. (2014) indicate that an Mw 7.75 earthquake on the Newport–Inglewood fault would cause 5 m/s of horizontal peak ground velocity (PGV) within the Los Angeles basin. However, the dynamic strain from this event would take much of the uppermost few hundred meters of basin rock beyond its f...

Strong seismic waves bring rock into frictional failure at the uppermost few hundred meters. Numerous small fractures slip with the cumulative effect of anelastic strain and nonlinear attenuation; these fractures should not distinguish between remote sources of stress. Still, frictional failure criteria are not evident especially when seismic waves...

Strong tidal stresses brought much of the icy shell of Enceladus into frictional failure at past times of high orbital eccentricity. The frictional behavior of shallow terrestrial rock exposed to repeated episodes of strong seismic waves provides analogy. Frictional failure produces cracks that lower the shear modulus. Seismic regolith develops whe...

Much of the Earth's mantle was melted in the Moon-forming impact. Gases that were not partially soluble in the melt, such as water and CO2, formed a thick, deep atmosphere surrounding the post-impact Earth. This atmosphere was opaque to thermal radiation, allowing heat to escape to space only at the runaway greenhouse threshold of approximately 100...

Strong seismic waves produce frictional failure within shallow pervasively cracked rocks. Distributed failure preferentially relaxes ambient tectonic stresses, providing a fragility measure of past strong shaking. Relaxation of the regional fault-normal compression appears to have occurred within granite from 768 m down to ~1000-1600 m depth at the...

Lithospheric structure changes at low spreading rates (<40 mm a-1), such that steady state molten rock cannot exist above the normal Moho depth of ~6 km. Dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable. One import...

The JamesWebb Space Telescope is slated for launch in 2018. Working primarily in the infrared, the James Webb will search for the first bright objects of the early Universe, examine how galaxies evolve, study the birth and development of stars, and investigate the physical properties of star systems as they relate to the building blocks of life. An...

Archean asteroid impacts, reflected in the presence of spherule beds in the 3.2-3.5 Ga Barberton greenstone belt (BGB), South Africa [Lowe et al., 2003], generated extreme seismic waves. Spherule bed S2 provides a field example. It locally lies at the contact between the Overwacht and Fig Tree Groups in the BGB, which formed as a result of the impa...

We obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate wit...

Detection of antineutrinos from U and Th series decay within the Earth (geoneutrinos) constrains the absolute abundance of these elements. Marine detectors will measure the ratio over the mantle beneath the site and provide spatial averaging. The measured mantle Th/U may well be significantly below its bulk earth value of ~4; Pb isotope measurement...

Cosmic collisions between terrestrial planets resemble somewhat the life cycle of the phoenix: worlds collide, are consumed in flame, and after the debris has cleared, shiny new worlds emerge aglow with possibilities. And glow they do, for they are molten. How brightly they glow, and for how long, is determined by their atmospheres, and by their mo...

Distributed anelastic deformation accommodates long-term motion in the "lid" region above blind faults. The flowing sequence of cyclic processes may lead to self-organization within lids composed of quartz-rich clay-bearing sedimentary rocks. Coseismic slip on the deep fault imposes strain and displacement on the lid. Sufficient strain brings the l...

Great outer rise earthquakes are a tsunami hazard as they occur on steeply dipping faults (Lay et al., 2009). The largest instrumentally recorded of these events are the 1933 Sanriku Japan earthquake (Mw = 8.4) and 1977 Sumba Indonesia earthquake (Mw = 8.3) (Lay et al., 2009). Seafloor bathymetry (Kobayashi et ai, 1998) and plate kinematics indicat...

Rate and state friction formalism represents the dependence of macroscopic shear traction τM on sliding velocity V and the history of the sliding surface. In macroscopic terms, τM = PN[μ0 + a ln(V/Vref) + b ln(ψ/ψnorm)], where PN is normal traction, μ0 is the coefficient of friction, a ≈ b ≈ 0.01 are small dimensionless parameters, Vref is a refere...

Life inhabits the subsurface of the Earth down to depths where temperature precludes it. Similar conditions are likely to exist within the traditional habitable zone for objects between 0.1 Earth mass (Mars) and 10 Earth masses (superearth). Long-term cooling and internal radioactivity maintain surface heat flow on the Earth. These heat sources are...

Analog station LUC near Lucerne, California, recorded strong motions from the nearby (1.25 km) fault rupture during the 28 June 1992 Landers mainshock. The records illustrate general issues that can arise at near-field stations. In the area of the station, weathered granite regolith with 400 m/s S-wave velocity overlies intact granite with 3000 m/s...

Venus’s descent into hellish heat must have been caused by its proximity to the Sun. The story of how Venus lost its water becomes: too much sunlight caused a runaway greenhouse effect, any water evaporated, and the hydrogen escaped into space.

Solid, liquid, and gaseous products of life's metabolic processes have a profound effect on the chemistry of Earth and its fluid envelopes. Earth's mantle has been modified by the ubiquitous influence of life on recycled lithosphere, with dramatic changes resulting from subduction of redox-sensitive minerals following the rise of photosynthetic oxy...

The end-Permian extinction decimated up to 95% of carbonate shell-bearing marine species and 80% of land animals. Isotopic excursions, dissolution of shallow marine carbonates, and the demise of carbonate shell-bearing organisms suggest global warming and ocean acidification. The temporal association of the extinction with the Siberia flood basalts...

Cracking within shallow compliant fault zones self-organizes so that strong dynamic stresses marginally exceed the elastic limit. To the first order, the compliant material experiences strain boundary conditions imposed by underlying stiffer rock. A major strike-slip fault yields simple dimensional relations. The near-field velocity pulse is essent...

The S-wave velocity in the shallow subsurface within seismically active regions self-organizes so that typical strong dynamic shear stresses marginally exceed the Coulomb elastic limit. The dynamic velocity from major strike-slip faults yields simple dimensional relations. The near-field velocity pulse is essentially a Love wave. The dynamic shear...

Strong seismic waves cause frictional failure within regolith on hillslopes. The material responds anelastically to the combined oscillating dynamic and static gravitational stresses. Gravity drives preferential downslope movement of the transiently weakened material. The net effect over many earthquake cycles is a tens of meter thick slow landslid...

Submarine hydrothermal vents above serpentinite produce chemical potential gradients of aqueous and ionic hydrogen, thus providing a very attractive venue for the origin of life. This environment was most favourable before Earth's massive CO(2) atmosphere was subducted into the mantle, which occurred tens to approximately 100 Myr after the moon-for...

Small-scale convection transfers heat from the asthenosphere into the base of the lithosphere. Scaling constraints are obtained on features associated with such convection that may be resolved by seismic studies. Compact notation arises by simply representing rheology: viscosity changes by a factor of e with a temperature increase of Teta and the m...

Replying to C. T. Reinhard & N. J. Planavsky Nature 474, doi:10.1038/nature09959 (2011); N. Dauphas & J. F. Kasting Nature 474 doi:10.1038/nature09960 (2011); C. Goldblatt & K. Zahnle Nature 474 doi:10.1038/nature09961 (2011) Reinhard and Planavsky1 and Dauphas and Kasting2 question whether the formation of Fe2+/Fe3+-rich sediments and the preserv...

Most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an "aqua planet" like Earth, the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that "land planets" (desert worlds with limited surface water) have wider habitable zones tha...

Small-scale convection supplies heat flow of ∼17 mW m−2 to the base of stable continents where xenolith studies resolve the geotherm. However, effects of small-scale convection are difficult to resolve in ocean basins. On first pass, most seafloor appears to subside to an asymptote compatible with ∼40 mW m−2 convective heat flow. These common regio...

Some basic questions about Archean plate tectonics can be addressed by examining accretionary Archean margins, in particular fault zones with significant strike-slip components on the Canadian Shield. (1) Were the oceanic plates typically rigid like modern plates? Yes. Significant lateral viscosity contrasts in the lithosphere between plates and pl...

The Earth became habitable once CO2 could be subducted into the deep mantle. It is likely that the Earth's surface became clement or even frigid within a few million years after it cooled to habitable temperatures (less than 120°C). Early life obtained its energy from chemical disequilibrium produced by internal processes within the Earth and photo...

Of the many volcanic chains on the Pacific plate, only two have a demonstrable long-lived (>70 million-year- long) age progression: the Hawaiian-Emperor chain of the northwestern Pacific and the Louisville chain of the southwestern Pacific. Paleomagnetic data, plate circuits, sediment facies and geodynamic modeling indicate rapid southward motion o...

The formalism of stagnant-lid convection provides a framework for interpreting seismic studies of the base of the lithosphere. Most of the lithosphere behaves as a rigid conducting lid. The rheological boundary layer lies between the lid and the more adiabatic asthenosphere. The properties of the rheological boundary layer control the vigor of conv...

Modern theories of planetary accumulation do not build Venus dry and Earth wet save by unlucky chance. If Venus and Earth were built of the same stuff, Venus's descent into ruin must have been caused by its proximity to the Sun: too much sunlight brought a runaway greenhouse effect, the oceans and seas evaporated, and the hydrogen in the water was...

Strong seismic waves produce frequent episodes of transient oscillating dynamic stress in the shallow subsurface within seismically active areas. Dynamic stress drives slip on a network of preexisting small fracture planes and leaves residual stresses once shaking ceases. The residual stresses act as prestresses during the next strong earthquake. L...

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1973. Vita. Includes bibliographical references (leaves 198-227).

Porous brittle rocks fail in shear and compaction. Rate and state friction describes such failure on a planar surface, while end-cap failure describes the failure of a continuum. Both formalisms include Coulomb failure in shear at low normal tractions. Rate and state friction includes slow compaction of gouge by normal traction when shearing is not...

A sparse geological record combined with physics and molecular phylogeny constrains the environmental conditions on the early Earth. The Earth began hot after the moon-forming impact and cooled to the point where liquid water was present in approximately 10 million years. Subsequently, a few asteroid impacts may have briefly heated surface environm...

Strain within certain major exhumed fault zones concentrated within a ∼1 mm wide permanent slip zone. A surrounding 10 mm thick fault core is strongly damaged. Concentration of seismic strain rate within a very thin zone is expected both for rate and state friction and weakening of the slip zone by flash melting at real contacts. In both cases, the...

There is ample geological evidence that Earth's climate resembled the present during the Archaean, despite a much lower solar luminosity. This was cast as a paradox by Sagan and Mullen in 1972. Several solutions to the paradox have been suggested, mostly focusing on adjustments of the radiative properties of Earth's atmosphere e.g. Kasting (1993),...

We are deeply disturbed by the recent escalation of political assaults on scientists in general and on climate scientists in particular. All citizens should understand some basic scientific facts. There is always some uncertainty associated with scientific conclusions; science never absolutely proves anything. When someone says that society should...

Photosynthesis produces effects that are evident in the oxidation state of crustal rocks and the trace element and isotopic chemistry of mantle-derived magmas.I attempt to correlate events in the geological record with genomic events.

Environmental niches in which life first emerged and later evolved on the Earth have undergone dramatic changes in response to evolving tectonic/geochemical cycles and to biologic interventions, as well as increases in the Sun's luminosity of about 25 to 30 per cent over the Earth's history. It has been inferred that the greenhouse effect of atmosp...

Numerical calculations and observations indicate that surface waves reverberate within sedimentary basins. A site response approach is inapplicable to the nonlinear attenuation of these waves as the energy passes repeatedly through the shallow subsurface. Computed dynamic stresses obtained by using published ShakeOut calculations (Graves et al., 20...

We propose the Chaotian Eon to demarcate geologic time from the origin of the Solar System to the Moon-forming impact on Earth. This separates the solar system wide processes of planet formation from the subsequent divergent evolution of the inner planets. We further propose the division of the Hadean Eon into eras and periods and naming the proto-...

Recent high precision ¹⁴²Nd isotope measurements showed that global silicate differentiation may have occurred as early as 30—75 Myr after the Solar System formation [Bennett V, et al. (2007) Science 318:1907—1910]. This time scale is almost contemporaneous with Earth's core formation at ˷30 Myr [Yin Q, et al. (2002) Nature 418:949—952]. The ¹⁸²Hf-...

The thermal subsidence of basins formed above thick continental lithosphere differs from that of young passive margin basins and of young oceanic crust in that stagnant lid convection supplies significant heat flow from the asthenosphere. The lithosphere eventually approaches thermal equilibrium where the convective heat added to its base balances...

The traditional habitable zone lies between an inner stellar radius where the surface of the planet becomes too hot for liquid water carbon-based life and on outer radius, where the surface freezes. It is effectively the zone where photosynthesis is feasible. The concept extends to putative life on objects with liquid methane at the surface, like T...

The atmosphere of the Earth passed from rock vapor after the moon-forming impact, eventually to clement conditions. A solid surface froze after ~10 m.y., when tidal heating waned. Much of the Earth's CO2 and water remained in the atmosphere. Soon thereafter the atmosphere cooled to ~500 K with a liquid water ocean and a ~100 bar CO2 greenhouse. Fur...

We propose the Chaotian Eon to demarcate geologic time from the origin of the Solar System to the Moon-forming impact on Earth. This separates the solar system wide processes of planet formation from the subsequent divergent evolution of the inner planets. We further propose the division of the Hadean Eon into eras and periods and naming the proto-...

The current (and past) mantle adiabat beneath continents is hot enough that ascending carbonate-rich domains partially melt liberating kimberlites. Over the last 2 Ga, most of these kimberlites have been trapped and frozen in the deep continental lithosphere, forming a massive CO2 reservoir. Geochemical studies of kimberlites that reached the surfa...

Changes in the S-P delay of repeating earthquakes near Parkfield, California, after strong shaking in the 2004 mainshock, occur at surface stations but not at borehole stations. This result indicates that rock damage occurs mainly in the upper few tens of meters in fractured rock with a low seismic velocity. In addition, changes in coda-primary del...

The thermal evolution of the lithospheric slab at subduction zones and its geophysical effects are numerically calculated. An alternating-direction, implicit, finite-difference scheme is used to compute the thermal models taking into account all heating sources and phase boundaries. These models, with the appropriate spreading rates and dip angles,...

Bends in volcanic hotspot lineaments, best represented by the large elbow in the Hawaiian-Emperor chain, were thought to directly record changes in plate motion. Several lines of geophysical inquiry now suggest that a change in the locus of upwelling in the mantle induced by mantle dynamics causes bends in hotspot tracks. Inverse modeling suggests...

Studies of kimberlite clan rocks indicate extensive reaction of these magmas with the deep lithosphere (Francis and Patterson, Lithos 2008). Heat balance constraints indicate implies that this process implies a major geochemical deep lithospheric reservoir for CO2. Stagnant-lid (including chemical-lid) convection supplies heat to the base of contin...

Photosynthesis has had geologic consequences over the Earth's history. In addition to modifying Earth's atmosphere and ocean chemistry, it has also modulated tectonic processes through enhanced weathering and modification of the nature and composition of sedimentary rocks within fold mountain belts and convergent margins. Molecular biological studi...

We obtain scaling relationships for convection beneath a chemically distinct conducting lid and compare this situation with isochemical stagnant lid convection. In both cases, the vigor of convection depends upon the small temperature contrast across the actively convecting rheological boundary layer, that is, ΔTrheo, the temperature difference bet...

Geologists observe a transition at full spreading rates of 10-15 mm/yr between slow ridge axes with a normal thickness of oceanic crust (ca. 6 km) and ultraslow ridge axes with a thinner crust and outcropping mantle peridotites. I examine this transition with 2-D kinematic thermal models. The fate of the basaltic magma has a major effect on the tem...

Strong seismic waves cause nonlinear behavior in the shallow subsurface in fractured rocks. Seismologists use low-amplitude signals from small repeating earthquakes to measure S wave velocity decrease after strong motion. The 2004 Parkfield, California, earthquake provides examples of such velocity changes in fractured sandstone with an S wave velo...

Chains of volcanic edifices lie along flow lines between plume-fed hot spots and the thin lithosphere at ridge axes. Discovery and Euterpe/Musicians Seamounts are two examples. An attractive hypothesis is that buoyant plume material flows along the base of the lithosphere perpendicular to isochrons. The plume material may conceivably flow in a broa...

Pre-photosynthetic niches were meagre with a productivity of much less than 10(-4) of modern photosynthesis. Serpentinization, arc volcanism and ridge-axis volcanism reliably provided H(2). Methanogens and acetogens reacted CO(2) with H(2) to obtain energy and make organic matter. These skills pre-adapted a bacterium for anoxygenic photosynthesis,...

A brief pulse of extreme acceleration ~20 m s-2 was recorded at Station FZ16 during the 2004 M w 6.0 Parkfield, California, earthquake. The sustained acceleration at the dominant frequency is a factor of ~2 below the maximum. Here we show that the pulses of extreme acceleration might originate in the shallow subsurface, rather than on the main faul...

The shallow habitable region of cratonal crust deforms with a strain rate on the order of approximately 10(19) s(1). This is rapid enough that small seismic events are expected on one-kilometer spatial scales and one-million-year timescales. Rock faulting has the potential to release batches of biological substrate, such as dissolved H(2), permitti...

The tectonic mechanisms of heat escape have evolved over time as the Earth's interior cooled. The Earth condensed from rock vapor to liquid magma in a few t-housand years following the Moon-forming impact, ∼4.5 billion years ago. The liquid magma convected vigorously and cooled rapidly, cooling the Earth in a few million years to mostly solid mush-...

Numerous linear chains of volcanoes are perpendicular to the isochrons of oceanic plates. As lithospheric thickness increases with plate age, these "flowline" hotspots are frequently attributed to the flow of buoyant plume material along the base of the lithosphere. Here the base of the lithosphere forms an upside-down drainage pattern for plume ma...

Shear from flow in the mantle tilts the conduits of mantle plumes. The density stratification at the top of the plume conduit is then unstable in cross section with cold material over hot. This stratification drives cross-stream convection. Such convection including the Stokes' law rise of the plume conduit through the ambient mantle readily mixes...

The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission to image planetary systems of nearby stars simultaneously in a few wide spectral bands covering the visible light (0.4-0.9 μm). It achieves its power by combining a high accuracy wavefront control system with a highly efficient Phase-Induced Amplitude Apodization (PIAA) c...

We address the first several hundred million years of Earth's history. The Moon-forming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over similar to 1,000 yrs. As it cooled the Earth degassed its volatiles into the atmosphere. It took another similar to 2 Myrs for the magma ocean to freeze at the surface. The c...