Stochastic accretion of the Earth

2020 ◽  
Author(s):  
Paolo Sossi ◽  
Ingo Stotz ◽  
Seth Jacobson ◽  
Alessandro Morbidelli ◽  
Hugh O'Neill
Keyword(s):  
Building Blocks ◽  
Physical Processes ◽  
Volatile Elements ◽  
Volatile Element ◽  
Elemental Abundances ◽  
Stable Isotope Fractionation ◽  
The Earth ◽  
Gravitational Pull ◽  
Atmospheric Loss ◽  
Impact Events

<p>The Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. Abundances of volatile elements descend roughly log-linearly with their calculated volatilities during solar nebula condensation [1, 2]. This depletion, however, is not accompanied by any stable isotope fractionation, which would otherwise be expected during vaporisation/condensation and atmospheric loss attending accretion [3, 4]. Thus, the physical processes that led to the formation of the Earth are yet to be reconciled with its chemical composition. Here, we integrate N-body simulations of planetary formation [5] within a framework that combines estimates for the compositions of planetary building blocks with volatile element losses during collisions, to link Earth’s elemental- and isotopic make-up with accretion mechanisms. The smooth pattern of volatile depletion in the Earth reflects the stochastic accretion of numerous, smaller, partially-vaporised precursor bodies whose elemental abundances are set by the heliocentric distances at which they formed. Impact events engender vaporisation, but atmospheric loss is only efficient during the early stages of accretion when volatile species can readily escape the gravitational pull of the proto-Earth. The chemical and isotopic compositions of the most volatile elements are controlled by that of late-accreting material, during which time the proto-Earth is sufficiently large so as to limit atmospheric loss. Stable isotopes of moderately- and highly volatile elements thus retain near-chondritic compositions.</p> <p>[1] O’Neill and Palme (2008), <em>Phil. Trans. R. Soc.</em> 4205-38 [2] Braukmüller et al. (2019), <em>Nat. Geosci.</em>, 564-9 [3] Wang and Jacobsen (2016), <em>Nature</em>, 521-4 [4] Sossi et al. 2018, <em>Chem. Geol.</em> 73-84 [5] Jacobson and Morbidelli (2014), <em>Phil. Trans. R. Soc.</em> 20130174</p>

scholarly journals Complex Brines and Their Implications for Habitability

Life ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 847
Author(s):  
Nilton O. Renno ◽  
Erik Fischer ◽  
Germán Martínez ◽  
Jennifer Hanley
Keyword(s):  
Hydrothermal Vents ◽  
Eutectic Temperature ◽  
Saline Water ◽  
Volatile Elements ◽  
Form Complex ◽  
Shallow Subsurface ◽  
Elemental Abundances ◽  
The Earth ◽  
Theoretical Evidence ◽  
Life On Earth

There is evidence that life on Earth originated in cold saline waters around scorching hydrothermal vents, and that similar conditions might exist or have existed on Mars, Europa, Ganymede, Enceladus, and other worlds. Could potentially habitable complex brines with extremely low freezing temperatures exist in the shallow subsurface of these frigid worlds? Earth, Mars, and carbonaceous chondrites have similar bulk elemental abundances, but while the Earth is depleted in the most volatile elements, the Icy Worlds of the outer solar system are expected to be rich in them. The cooling of ionic solutions containing substances that likely exist in the Icy Worlds could form complex brines with the lowest eutectic temperature possible for the compounds available in them. Indeed, here, we show observational and theoretical evidence that even elements present in trace amounts in nature are concentrated by freeze–thaw cycles, and therefore contribute significantly to the formation of brine reservoirs that remain liquid throughout the year in some of the coldest places on Earth. This is interesting because the eutectic temperature of water–ammonia solutions can be as low as ~160 K, and significant fractions of the mass of the Icy Worlds are estimated to be water substance and ammonia. Thus, briny solutions with eutectic temperature of at least ~160 K could have formed where, historically, temperature have oscillated above and below ~160 K. We conclude that complex brines must exist in the shallow subsurface of Mars and the Icy Worlds, and that liquid saline water should be present where ice has existed, the temperature is above ~160 K, and evaporation and sublimation have been inhibited.

scholarly journals Origins and Early Evolution of the Atmosphere and the Oceans

2020 ◽  
Vol 9 (2) ◽  
pp. 135-313
Author(s):  
Bernard Marty
Keyword(s):  
Solar System ◽  
Solar Nebula ◽  
Noble Gases ◽  
Building Blocks ◽  
Anthropogenic Activity ◽  
Outer Solar System ◽  
Volatile Elements ◽  
Isotopic Signatures ◽  
Early Atmosphere ◽  
The Earth

My journey in science began with the study of volcanic gases, sparking an interest in the origin, and ultimate fate, of the volatile elements in the interior of our planet. How did these elements, so crucial to life and our surface environment, come to be sequestered within the deepest regions of the Earth, and what can they tell us about the processes occurring there? My approach has been to establish geochemical links between the noble gases, physical tracers par excellence, with major volatile elements of environmental importance, such as water, carbon and nitrogen, in mantle-derived rocks and gases. From these analyses we have learned that the Earth is relatively depleted in volatile elements when compared to its potential cosmochemical ancestors (e.g., ~2 ppm nitrogen compared to several hundreds of ppm in primitive meteorites) and that natural fluxes of carbon are two orders of magnitude lower than those emitted by current anthropogenic activity. Further insights into the origin of terrestrial volatiles have come from space missions that documented the composition of the proto-solar nebula and the outer solar system. The consensus behind the origin of the atmosphere and the oceans is evolving constantly, although recently a general picture has started to emerge. At the dawn of the solar system, the volatile-forming elements (H, C, N, noble gases) that form the majority of our atmosphere and oceans were trapped in solid dusty phases (mostly in ice beyond the snowline and organics everywhere). These phases condensed from the proto-solar nebula gas, and/or were inherited from the interstellar medium. These accreted together within the next few million years to form the first planetesimals, some of which underwent differentiation very early on. The isotopic signatures of volatiles were also fixed very early and may even have preceded the first episodes of condensation and accretion. Throughout the accretion of the Earth, volatile elements were delivered by material from both the inner (dry, volatile-poor) and outer (volatile-rich) solar system. This delivery was concomitant with the metals and silicates that form the bulk of the planet. The contribution of bodies that formed in the far outer solar system, a region now populated by comets, is likely to have been very limited. In that sense, volatile elements were contributed continuously throughout Earth’s accretion from inner solar system reservoirs, which also provided the silicates and metal building blocks of the inner planets. Following accretion, it likely took a few hundred million years for the Earth’s atmosphere and oceans to stabilise. Luckily, we have been able to access a compositional record of the early atmosphere and oceans through the analysis of palaeo-atmospheric fluids trapped in Archean hydrothermal quartz. From these analyses, it appears that the surface reservoirs of the Earth evolved due to interactions between the early Sun and the top of the atmosphere, as well as the development of an early biosphere that progressively altered its chemistry.

scholarly journals The Frequency and Predicted Consequences of Cosmic Impacts in the Last 65 Million Years

2004 ◽  
Vol 213 ◽  
pp. 289-294
Author(s):  
Michael Paine ◽  
Benny Peiser
Keyword(s):  
Financial Support ◽  
Global Climate ◽  
Catastrophic Event ◽  
The Past ◽  
The Earth ◽  
Global Events ◽  
Impact Events

Sixty five million years ago a huge asteroid collided with the Earth and ended the long reign of the dinosaurs. In the aftermath of this catastrophic event, the mammals arose and eventually mankind came to dominate the surface of the planet. The Earth, however, has not been free from severe impacts since the time of the dinosaur killer. We examine the likely frequency of major impact events over the past 65 million years, the evidence for these impacts and the predicted consequences of various types of impacts. It is evident that the mammals had to survive frequent severe disruptions to the global climate, and it is likely that over the past 5 million years hominids were faced with several catastrophic global events. Smaller but strategically located impact events could bring down our civilisation if they occurred today. Mankind has recently developed the expertise to predict and mitigate future impacts, but political and financial support are lacking.

General discussion after session V

1988 ◽  
Vol 325 (1587) ◽  
pp. 611-618 ◽  
Keyword(s):  
Origin Of Life ◽  
Time Perspective ◽  
Applied Mathematics ◽  
Building Blocks ◽  
Living Systems ◽  
Organic Chemical ◽  
General Terms ◽  
The Earth ◽  
The Origin Of Life ◽  
Emergence Of Life

N. C. Wickramasinghe ( Department of Applied Mathematics and Astronomy, University College, Cardiff, U. K. ). The question of the origin of life is, of course, one of the most important scientific questions and it is also one of the most difficult. One is inevitably faced here with a situation where there are very few empirical facts of direct relevance and perhaps no facts relating to the actual transition from organic material to material that can even remotely be described as living. The time perspective of events that relate to this problem has already been presented by Dr Chang. Uncertainty still persists as to the actual first moment of the origin or the emergence of life on the Earth. At some time between 3800 and 3300 Ma BP the first microscopic living systems seem to have emerged. There is a definite moment in time corresponding to a sudden appearance of cellular-type living systems. Now, traditionally the evolution of carbonaceous compounds which led to the emergence of life on Earth could be divided into three principal steps and I shall just remind you what those steps are. The first step is the production of chemical building blocks that lead to the origin of the organic molecules necessary as a prerequisite for the evolution of life. Step two can be described in general terms as prebiotic evolution, the arrangement of these chemical units into some kind of sequence of precursor systems that come almost up to life but not quite; and then stage three is the early biological evolution which actually effects the transition from proto-cellular organic-type forms into truly cellular living systems. The transition is from organic chemistry, prebiotic chemistry to biochemistry. Those are the three principal stages that have been defined by traditional workers in the field, the people who, as Dr Chang said, have had the courage to make these queries and attempt to answer them. Ever since the classic experiments where organic materials were synthesized in the laboratory a few decades back, it was thought that the first step, the production of organic chemical units, is important for the origin of life on the Earth, and that this had to take place in some location on the Earth itself.

The place of geophysics in the university - an academics view

1971 ◽  
Vol 2 (2) ◽  
pp. 45
Author(s):  
S.H. Hall
Keyword(s):  
Physical Oceanography ◽  
Physical Processes ◽  
Ionospheric Physics ◽  
The Earth ◽  
The University

If one seeks in any dictionary the meaning of geophysics, it is difficult, to my mind, to find an entirely satisfying one. One I found was the 'study of physical processes relating to the Earth'. A better one I feel would read 'the study of physical processes, state and properties relating to the Earth' ---. Most geophysicists not long ago insisted that this definition included the aesthenosphere, 1ithosphere, atmosphere, ionosphere, magnetosphere etc. -- if one judges by the contents of some geophysical journals, and thereby considered physical oceanography, meteorology, ionospheric physics, etc. as aspects of the all-embracing title-geophysics. In speaking on this topic as it relates to a department of geology, I should add that they have not had the temerity to include geology as a further aspect.

Volatile element chemistry during accretion of the earth

Geochemistry ◽  
2020 ◽  
Vol 80 (1) ◽  
pp. 125594 ◽  
Author(s):  
Bruce Fegley ◽  
Katharina Lodders ◽  
Nathan S. Jacobson
Keyword(s):  
Volatile Element ◽  
The Earth ◽  
Element Chemistry

High frequency radio emissions as a manifestation of physical processes in the auroral plasma

2020 ◽  
Author(s):  
Hanna Rothkaehl ◽  
Barbara Matyjasiak ◽  
Agata Chuchra ◽  
Roman Schreiber ◽  
Michał Marek ◽  
...  
Keyword(s):  
Auroral Oval ◽  
Physical Processes ◽  
Radio Emissions ◽  
Structure And Dynamics ◽  
Auroral Kilometric Radiation ◽  
The Earth ◽  
Auroral Plasma ◽  
Auroral Roar ◽  
Physical Plasma ◽  
Maximum Occurrence

<p>The Earth’s auroral region and its close neighbourhood is the origin of strong radio emissions caused by complex physical plasma processes. Among them we can list auroral hiss, auroral roar, auroral medium frequency (MF) burst, and auroral kilometric radiation (AKR).  Analysis of such emissions can provide information about magnetospheric structure and dynamics. </p><p>In this work we present selected cases of Earth’s AKR-like radio emissions observed by RELEC  and mission at the top side ionosphere leyers. The emissions are seen at frequencies of the order of hundreds of kHz in the ionosphere, just below the auroral oval and  can be observed not only in disturbed geomagnetic conditions, but also during quiet periods. The maximum occurrence is at ∼ 75 ◦ invariant latitude and can have extent up to ∼ 11 ◦ in invariant latitude.</p><p> </p>

A Deep Learning Technique for Automated Detection of ULF Waves in Swarm Time Series

2020 ◽  
Author(s):  
Alexandra Antonopoulou ◽  
Constantinos Papadimitriou ◽  
Georgios Balasis ◽  
Adamantia Zoe Boutsi ◽  
Konstantinos Koutroumbas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Deep Learning ◽  
Building Blocks ◽  
Data Availability ◽  
Topside Ionosphere ◽  
Ulf Waves ◽  
Dense Layer ◽  
Ulf Wave ◽  
The Earth ◽  
Swarm Satellites

<p>Ultra-low frequency (ULF) magnetospheric plasma waves play a key role in the dynamics of the Earth’s magnetosphere and, therefore, their importance in Space Weather studies is indisputable. Magnetic field measurements from recent multi-satellite missions (e.g. Cluster, THEMIS, Van Allen Probes and Swarm) are currently advancing our knowledge on the physics of ULF waves. In particular, Swarm satellites, one of the most successful mission for the study of the near-Earth electromagnetic environment, have contributed to the expansion of data availability in the topside ionosphere, stimulating much recent progress in this area. Coupled with the new successful developments in artificial intelligence (AI), we are now able to use more robust approaches devoted to automated ULF wave event identification and classification. The goal of this effort is to use a deep learning method in order to classify ULF wave events using magnetic field data from Swarm. We construct a Convolutional Neural Network (CNN) that takes as input the wavelet spectra of the Earth’s magnetic field variations per track, as measured by each one of the three Swarm satellites, and whose building blocks consist of two convolution layers, two pooling layers and a fully connected (dense) layer, aiming to classify ULF wave events in four different categories: 1) Pc3 wave events (i.e., frequency range 20-100 MHz), 2) non-events, 3) false positives, and 4) plasma instabilities. Our primary experiments show promising results, yielding successful identification of more than 95% accuracy. We are currently working on producing larger training/test datasets, by analyzing Swarm data from the mid-2014 onwards, when the final constellation was formed, aiming to construct a dataset comprising of more than 50000 wavelet image inputs for our network.</p>

Ice lines and the formation of Uranus and Neptune

2020 ◽  
Author(s):  
Olivier Mousis ◽  
Artyom Aguichine ◽  
Ravit Helled ◽  
Patrick Irwin ◽  
Jonathan I. Lunine
Keyword(s):  
Chemical Composition ◽  
Transport Model ◽  
Outer Region ◽  
Building Blocks ◽  
Planetary Formation ◽  
Physical Conditions ◽  
Elemental Abundances ◽  
Self Consistent ◽  
Protosolar Nebula ◽  
Do So

<p>We aim at investigating whether the chemical composition of the outer region of the protosolar nebula can be consistent with current estimates of the elemental abundances in the ice giants. To do so, we use a self-consistent evolutionary disc and transport model to investigate the time and radial distributions of H<sub>2</sub>O, CO, N<sub>2</sub>, and H<sub>2</sub>S, i.e., the main O-, C-, N, and S-bearing volatiles in the outer disc. We show that it is impossible to accrete a mixture composed of gas and solids from the disc with a C/H ratio presenting enrichments comparable to the measurements (70 times protosolar). We also find that the C/N and C/S ratios measured in Uranus and Neptune are compatible with those acquired by building blocks agglomerated from grains and pebbles condensed in the vicinities of N<sub>2</sub> and CO ice lines in the nebula. In contrast, the presence of protosolar C/N and C/S ratios in Uranus and Neptune would imply that their building blocks agglomerated from particles condensed at higher heliocentric distances. Our study demonstrates the importance of measuring the elemental abundances in the ice giant atmospheres, as they can be used to trace the planetary formation location and/or the chemical and physical conditions of the protosolar nebula.<span class="Apple-converted-space"> </span></p>

Sign in / Sign up

Export Citation Format

Share Document