Cosmic composites: Rocks from space and their astonishing influence on earth and humanity

Meteorites are some of the most complex natural materials known. They are incredibly compositionally diverse rocks, ranging from chunks of almost pure iron and nickel metal, which derive from the cores of disrupted planetary bodies, to pristine collections of dust and ice that have existed virtually umolested since the birth of the Sun. Certain types of meteorites contain the oldest materials ever dated, and some even host the direct remnants of previous generations of stars that contributed material to build our Solar System. Meteorites are time capsules of information about Solar System history and evolution, and, simply put, are a scientific treasure trove. In addition, whereas most meteorites come from the scores of planetary bodies that now reside in the asteroid belt, some even represent samples that originate directly from our Moon and Mars. However, although the value of information we have gained about Earth and the Solar System from studying meteorites as scientific objects cannot be underestimated, the principal importance of meteorites to humanity is far more complex due to their oftentimes spectacular arrivals and important payloads. From a cultural perspective, many of the world’s ancient empires and most popular religions have inflection points in which meteorites played an important role, in some cases drastically altering the course of history. Christianity was an obscure cult followed by relatively few people until a timely meteoritic interaction changed its trajectory. The most venerated object in the Islamic faith almost certainly has a meteoritic origin, and for a short time, worship of a meteorite (adorned with fancy dressings and gemstones) was even the official religion of the Roman Empire. Wars have been waged (and ended) due to encounters with extraterrestrial materials. Temples have been built to honor fallen stones, and early cultures were enamored by the metal found in meteorites, as they did not yet know how to produce such metal themselves. These numerous overlaps between humans and meteorites were critical in shaping modern culture around the world, yet the most important contributions of meteorites to Earth started happening shortly after the planet formed ~4.5 billion years ago. If meteorites had not interacted with the Earth shortly after its formation, the Moon would not exist. Earth likely would not have liquid water at its surface or offer a habitable atmosphere. The continued bombardment of Earth by space rocks gives humans access to many of the precious metals crucial for modern technology—such as iridium, platinum, and gold—which would otherwise be thoroughly sequestered in Earth’s core and inaccessible for exploitation. In addition, and probably most importantly, meteorites were the primary delivery vehicles for the complex organic materials that eventually created the biosphere. Many of the organic building blocks thought essential for the emergence of life are present in primitive meteorites, with one sample alone hosting over 80 amino acids (known life uses only 20 of these). In addition, multiple nucleotide bases of both RNA and DNA as well as other vital biomolecules have been discovered in extraterrestrial specimens, indicating that the building blocks of life could have been created abiotically in the outer Solar System and delivered to Earth via meteorites. And, of course, a meteorite impact was influential to ending the long reign of the dinosaurs, paving the way for mammals to rapidly evolve and thrive, promptly taking over the helm as Earth’s dominant class of creature. In this presentation, I will discuss the immense influence meteorites have had on our planet, spanning from its creation to modern human culture. In addition, I will highlight some of the incredible scientific insights we have gained from the study of these unique materials, and some of the active areas of research in reconstructing the history and evolution of our Solar System

Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions

Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years

Uranium isotope ratios of Muonionalusta troilite and complications for the absolute age of the IVA iron meteorite core

The crystallization ages of planetary crustal material (given by basaltic meteorites) and planetary cores (given by iron meteorites) provide fiducial marks for the progress of planetary formation, and thus, the absolute ages of these objects fundamentally direct our knowledge and understanding of planet formation and evolution. The lone precise absolute age of planetary core material was previously obtained on troilite inclusions from the IVA iron meteorite Muonionalusta. This previously reported Pb–Pb age of 4565.3 ± 0.1 Ma—assuming a 238U/235U =137.88—only post-dated the start of the Solar System by approximately 2–3 million years, and mandated fast cooling of planetary core material. Since an accurate Pb–Pb age requires a known 238U/235U of the sample, we have measured both 238U/235U and Pb isotopic compositions of troilite inclusions from Muonionalusta. The measured 238U/235U of the samples range from ∼137.84 to as low as ∼137.22, however based on Pb and U systematics, terrestrial contamination appears pervasive and has affected samples to various extents for Pb and U. The cause of the relative 235U excess in one sample does not appear to be from terrestrial contamination or the decay of short-lived 247Cm, but is more likely from fractionation of U isotopes during metal–silicate separation during core formation, exacerbated by the extreme U depletion in the planetary core. Due to limited Pb isotopic variation and terrestrial disturbance, no samples of this study produced useful age information; however the clear divergence from the previously assumed 238U/235U of any troilite in Muonionalusta introduces substantial uncertainty to the previously reported absolute age of the sample without knowledge of the 238U/235U of the sample. Uncertainties associated with U isotope heterogeneity do not allow for definition of a robust age of solidification and cooling for the IVA core. However, one sample of this work—paired with previous work using short-lived radionuclides—suggests that the cooling age of the IVA core may be significantly younger than previously thought. This work indicates the metallic cores of protoplanetary bodies solidified no earlier than the first ∼5–10 million years of the Solar System.This work was supported by a Sofja Kovalevskaja award from the Alexander von Humboldt Foundation (G.A.B.)

Disk transport rates from Ti isotopic signatures of refractory inclusions

The early solar system was a dynamic period during which the formation of early solids set into motion the process of planet building. Although both astrophysical observations and theoretical modeling demonstrate the presence of widespread transport of material, we lack concrete quantitative constraints on timings, distances, and mechanisms thereof. To trace these transport processes, one needs objects of known early formation times and these objects would need to be distributed throughout parent bodies with known accretion times and distances. Generally, these criteria are met by “regular” (i.e., non–fractionated and unidentified nuclear and excluding hibonite‐rich) Ca‐Al‐rich inclusions (CAIs) as these objects formed very early and close to the young Sun and contain distinctive nucleosynthetic isotope anomalies that permit provenance tracing. However, nucleosynthetic isotopic signatures of such refractory inclusions have so far primarily been analyzed in chondritic meteorites that formed within ~4 AU from the Sun. Here, we investigate Ti isotopic signatures of four refractory inclusions from the ungrouped carbonaceous chondrite WIS 91600 that was previously suggested to have formed beyond ~10 AU from the Sun. We show that these inclusions exhibit correlated excesses in 50Ti and 46Ti and lack large Ti isotopic anomalies that would otherwise be indicative of more enigmatic refractory materials with unknown formation ages. Instead, these isotope systematics suggest the inclusions to be genetically related to regular CAIs commonly found in other chondrites that have a broadly known formation region and age. Collectively, this implies that a common population of CAIs was distributed over the inner ~10 AU within ~3.5 Myr, yielding an average (minimum) speed for the transport of millimeter‐scale material in the early solar system of ~1 cm s−1.Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Lawrence Livermore National Laboratory http://dx.doi.org/10.13039/10000622

Replication Data for: Lack of late-accreted material as the origin of 182W excesses in the Archean mantle: Evidence from the Pilbara Craton, Western Australia

• 182W and HSE indicate partial lack late-accreted material in Pilbara source. • Only of normal amount of late-accreted material present at 3.3 Ga. • Similar 182W characteristics of other mantle sources indicates common process. • 182W–HSE mismatch for other sources caused by dissimilar behaviors of HSE vs. W. • Moon and pre-late accretion BSE had similar 182W

Replication Data for: Lack of late-accreted material as the origin of 182W excesses in the Archean mantle: Evidence from the Pilbara Craton, Western Australia

• 182W and HSE indicate partial lack late-accreted material in Pilbara source. • Only of normal amount of late-accreted material present at 3.3 Ga. • Similar 182W characteristics of other mantle sources indicates common process. • 182W–HSE mismatch for other sources caused by dissimilar behaviors of HSE vs. W. • Moon and pre-late accretion BSE had similar 182W

Replication Data for: Lack of late-accreted material as the origin of 182W excesses in the Archean mantle: Evidence from the Pilbara Craton, Western Australia

• 182W and HSE indicate partial lack late-accreted material in Pilbara source. • Only of normal amount of late-accreted material present at 3.3 Ga. • Similar 182W characteristics of other mantle sources indicates common process. • 182W–HSE mismatch for other sources caused by dissimilar behaviors of HSE vs. W. • Moon and pre-late accretion BSE had similar 182W

Fossil records of early solar irradiation and cosmolocation of the CAI factory: A reappraisal

Calcium-aluminum–rich inclusions (CAIs) in meteorites carry crucial information about the environmental conditions of the nascent Solar System prior to planet formation. Based on models of 50V–10Be co-production by in-situ irradiation, CAIs are considered to have formed within ~0.1 AU from the proto-Sun. Here, we present vanadium (V) and strontium (Sr) isotopic co-variations in fine- and coarse-grained CAIs and demonstrate that kinetic isotope effects during partial condensation and evaporation best explain V isotope anomalies previously attributed to solar particle irradiation. We also report initial excesses of 10Be and argue that CV CAIs possess essentially a homogeneous level of 10Be, inherited during their formation. Based on numerical modeling of 50V–10Be co-production by irradiation, we show that CAI formation during protoplanetary disk build-up likely occurred at greater heliocentric distances than previously considered, up to planet-forming regions (~1AU), where solar particle fluxes were sufficiently low to avoid substantial in-situ irradiation of CAIs