Elements Covers

Thematic Articles

The Formation of the Solar Systems: A Recipe for Worlds

This paper summarises the recipe – the raw and processed ingredients plus some of the processes – behind making our solar system 4,600 million years ago. Like a gourmand recipe, the solar system formed from many disparate ingredients, many of these ingredients themselves being the products of complex processes. Thus, to create the habitable solar system we see today required extensive work and processing. However, unlike a food recipe, much of how this happened is poorly understood, although a combination of new observations and analysis is ensuring that progress continues to be made.

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Comets in the Path of Earth

Earth’s atmosphere offers little protection against comet impacts, because many comets are bigger than 1 km. Fewer comets hit Earth than asteroids of the same size, except perhaps for sizes larger than 10 km. Comets release copious amounts of solid debris called meteoroids, and these meteoroids disperse to form meteoroid streams, some of which cause meteor showers on Earth. Recent meteor shower observations reveal the presence of potentially dangerous parent comets and trace their dynamical evolution. In addition, some showers leave a signature of “cosmic dust” in our atmosphere.

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Organic Molecules and Volatiles in Comets

Organic molecules and volatiles (e.g. H2O, CO, CO2) are the major components of comets. The majority of the organic compounds found within comets were produced by ice irradiation in dense molecular clouds and in the protoplanetary disk prior to comet formation. Comets are essentially repositories of protocometary material. As a result, comets do not show the clear trends in chemical and isotopic compositions that would be expected from our understanding of their formation locations. Rather, comets record chemical evolution in the protoplanetary disk and allow us to unveil the formation history of the organics and volatiles.

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The Rosetta Mission and the Chemistry of Organic Species in Comet 67P/Churyumov-Gerasimenko

Comets are regarded as probably the most primitive of solar system objects, preserving a record of the materials from which the solar system aggregated. Key amongst their components are organic compounds – molecules that may trace their heritage to the interstellar medium from which the protosolar nebula eventually emerged. The most recent cometary space mission, Rosetta, carried instruments designed to characterize, in unprecedented detail, the organic species in comet 67P/Churyumov–Gerasimenko (67P). Rosetta was the first mission to match orbits with a comet and follow its evolution over time, and also the first mission to land scientific instruments on a comet surface. Results from the mission revealed a greater variety of molecules than previously identified and indicated that 67P contained both primitive and processed organic entities.

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Flyby Missions to Comets and Return Sample Analysis

Images from flyby missions show comets to be geomorphically diverse bodies that spew jets of gas, dust, and rocks into space. Comet surfaces differ from other small bodies because of their ejection of mass into space. Comet solids >2 µm are similar to primitive meteorite ingredients and include the highest temperature materials made in the early solar system. The presence of these materials in ice-rich comets is strong evidence for large-scale migration of solid grains in the early solar system. Cometary silicates appear to have formed in numerous hot solar system regions. Preserved interstellar grains are rare, unless they have eluded identification by having solar isotopic compositions

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Seeing Snails in a New Light

Luminescence is exhibited by many common minerals, some of which have been exploited for dating. Calcite has the potential to date events that occurred over millions of years, but a series of challenges has hindered its use in dating limestone building stones, speleothems, and mollusk shells. Now, however, promising results from calcite luminescence dating have been achieved from an unexpected source: the opercula grown by certain species of snail. Coupled with innovations in luminescence imaging systems, snail opercula offer an exciting new approach that may finally unlock calcite’s potential for dating.

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Luminescence Thermochronometry: Investigating the Link between Mountain Erosion, Tectonics and Climate

Luminescence thermochronometry is a recently developed method that can constrain erosion histories at sub-Quaternary timescales. Luminescence thermochronometry determines the timing and rate at which electrons are trapped and thermally released in minerals, in response to in situ radiation and rock cooling. Erosion histories can be inferred by translating rock cooling rates into an erosion rate using knowledge of the Earth’s thermal field. In this article, we use examples of luminescence thermochronometry applied to the Himalaya mountains, the New Zealand Alps and the Japanese Alps to infer (and link together) wider aspects of regional erosion, climate and tectonic activity.

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Timelines for Human Evolution and Dispersals

Luminescence dating has been instrumental in constraining the age of archaeological and human skeletal remains. Thermoluminescence dating was applied originally to heated pottery and burnt flint, and optical dating was developed subsequently to estimate the depositional age of sun-bleached sediments associated with artefacts and fossils. These methods have helped establish numerical timelines for human evolution and dispersals over the last half million years, including the earliest evidence for modern humans in Africa, Asia and Australia, and the comings and goings of archaic humans in Eurasia and Indonesia. Here, we recount the major role that luminescence dating has played recently in enriching our understanding of global human history.

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Dates and Rates of Earth-Surface Processes Revealed using Luminescence Dating

Understanding rates and variability of Earth-surface processes is vital to assessing natural hazards, landscape response to climate change and addressing concerns related to food security and water supply. Surface processes affect the critical zone, where life interacts with the land surface, and are archived in sediment records. Luminescence dating provides an age estimate for sediment deposition and can provide dates to calculate rates and recurrence intervals of natural hazards and Earth-surface processes. This method has produced robust age estimates from a wide range of terrestrial, marine, tectonic, and archaeological settings. Importantly, luminescence dating covers an age range that spans the last several decades to the last several hundred thousand years, providing critical rates and dates for evaluating processes that are important to society.

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