A collisional origin to Earth’s non-chondritic composition?

Bonsor, Amy; Leinhardt, Z. M.; Carter, Philip J.; Elliott, Tim; Walter, Michael J.; Stewart, S. T.

doi:10.1016/j.icarus.2014.10.019

Cited by 83 publications

(53 citation statements)

References 40 publications

(99 reference statements)

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“…• The Earth and its sister terrestrial planets have higher bulk Fe/Mg ratios than the Sun and most chondrite classes (including t he C I c ho nd r it e s), consistent with mantle stripping and consequent enhancement of the ratio of core to mantle observed in the simulations of Stewart and Leinhardt (2012) and Bonsor et al (2015).…”

Section: Whither Primitive Mantle?supporting

confidence: 62%

Probing the Earth’s Deep Interior Through Geochemistry

White¹

2015

Geochem. Persp.

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Section: Whither Primitive Mantle?supporting

confidence: 62%

Probing the Earth’s Deep Interior Through Geochemistry

White¹

2015

Geochem. Persp.

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“…However, if the EER does not exist within the planet, this reservoir was lost to space by collisional erosion by large impactors [16][17][18][19] . If so, Earth's mantle is far more depleted than commonly suggested.…”

Section: Earth's Radiogenic Heat Generation Is Between 18 and 45% Lowmentioning

confidence: 99%

“…Although the existence of the EER is required to satisfy the mass balance of a chondrite-based 3 Earth, no evidence of such a reservoir exists. If the modern bulk silicate Earth has a chondrite-based composition, the missing EER must have remained in the deep Earth, completely hidden, for >4.5 billion years (Gyr) of convective mantle stirring, melting, and volcanism.However, if the EER does not exist within the planet, this reservoir was lost to space by collisional erosion by large impactors [16][17][18][19] . If so, Earth's mantle is far more depleted than commonly suggested.…”

mentioning

confidence: 99%

Connections between the bulk composition, geodynamics and habitability of Earth

Jellinek

Jackson

2015

Nature Geosci

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NATURE GEOSCIENCE | ADVANCE ONLINE PUBLICATION | www.nature.com/naturegeoscience 1 T he growth, internal differentiation, and geodynamic evolution of our planet can be partly constrained by the average composition of the silicate part of Earth (bulk silicate Earth). This basic constraint on Earth's history is difficult to infer, however, because geochemists cannot adequately sample a planet composed of oceanic and continental crust, a compositionally heterogeneous mantle, and a core. Owing to the heterogeneous make-up of Earth and necessarily incomplete sampling of the accessible parts of Earth, one approach to predict the bulk silicate Earth composition is to use models for Earth's formation. A long-standing conceptual picture for Earth's composition assumes that it formed by accretion of chondritic precursors, which are the most primitive, undifferentiated objects in the solar system (Box 1). All classes of chondrites have relatively constant ratios of elements that are both refractory (elements with high condensation temperatures) and lithophile (elements that remain in the silicate portion of Earth, including the crust and mantle), such as Samarium (Sm) and Neodymium (Nd). These elements are not fractionated during condensation from a hot nebular gas 1-4 or during separation of a metallic core with relatively low sulphur concentrations 5 . Therefore, ratios of the refractory lithophile elements in the silicate Earth have long been assumed to be the same as in chondrites, and the bulk silicate Earth has chondritic Sm/Nd ratios (ref. 2). The 146 Sm-142 Nd decay scheme ( 146 Sm half-life = 68 to 103 million years; ref. 6) provides a way to test this model: if the bulk silicate Earth and the chondrite reservoir have the same Sm/Nd, the 142 Nd/ 144 Nd of Earth and ordinary chondrites should be the same. The discovery that the accessible, modern terrestrial mantle has 142Nd/ 144 Nd that is 18 ± 5 ppm (0.018 ± 0.005‰) higher than ordinary chondrites, which exhibit isotopic compositions representative of planetary building material 4,7,8 , challenges the assumption that Earth has chondritic Sm/Nd ratios (refs 9-12). While there are other models for the origin of the superchondritic 142 Nd/ 144 Nd in the bulk silicate Earth (Box 1), we explore the hypothesis that the higher 142 Nd/ 144 Nd in the modern terrestrial mantle relative to ordinaryThe bulk composition of the silicate part of Earth has long been linked to chondritic meteorites. Ordinary chondrites -the most abundant meteorite class -are thought to represent planetary building materials. However, a landmark discovery showed that the 142 Nd/ 144 Nd ratio of the accessible parts of the modern terrestrial mantle on Earth is greater than that of ordinary chondrites. If Earth was derived from these precursors, mass balance requires that a missing reservoir with 142 Nd/ 144 Nd lower than ordinary chondrites was isolated from the accessible mantle within 20 to 30 million years of accretion. This reservoir would host the equivalent of the modern continents' budget of ...

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“…and developed a state-of-the-art collisions model for gravitydominated bodies that essentially maps collision outcomes based on the masses, collision speed, and impact angle for a given two-body collision. This collision model has been implemented into an N-body tree code (Lines et al 2014;Bonsor et al 2015) and used to examine planetesimal formation. Chambers (2013) implemented this collision model into the widely used Mercury integration package (Chambers 2001).…”

Section: Introductionmentioning

confidence: 99%

The Frequency of Giant Impacts on Earth-Like Worlds

Quintana

Barclay

Borucki

et al. 2016

ApJ

147

140

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The late stages of terrestrial planet formation are dominated by giant impacts that collectively influence the growth, composition, and habitability of any planets that form. Hitherto, numerical models designed to explore these late stage collisions have been limited by assuming that all collisions lead to perfect accretion, and many of these studies lack the large number of realizations needed to account for the chaotic nature of N-body systems. We improve on these limitations by performing 280 simulations of planet formation around a Sun-like star, half of which used an N-body algorithm that has recently been modified to include fragmentation and hit-and-run (bouncing) collisions. We find that when fragmentation is included, the final planets formed are comparable in terms of mass and number; however, their collision histories differ significantly and the accretion time approximately doubles. We explored impacts onto Earth-like planets, which we parameterized in terms of their specific impact energies. Only 15 of our 164 Earth-analogs experienced an impact that was energetic enough to strip an entire atmosphere. To strip about half of an atmosphere requires energies comparable to recent models of the Moon-forming giant impact. Almost all Earth-analogs received at least one impact that met this criteria during the 2 Gyr simulations and the median was three giant impacts. The median time of the final giant impact was 43 Myr after the start of the simulations, leading us to conclude that the time-frame of the Moon-forming impact is typical among planetary systems around Sun-like stars.

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A collisional origin to Earth’s non-chondritic composition?

Cited by 83 publications

References 40 publications

Probing the Earth’s Deep Interior Through Geochemistry

Probing the Earth’s Deep Interior Through Geochemistry

Connections between the bulk composition, geodynamics and habitability of Earth

The Frequency of Giant Impacts on Earth-Like Worlds

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