Negative feedbacks are necessary to prevent Earth-like planets from becoming runaway greenhouses and runaway glaciations and thus uninhabitable. Different negative feedbacks could be operative over the habitable lifetime of a planet. The carbonate-silicate cycle has been invoked as a major negative feedback throughout Earth’s 4-billion-year history. It is likely that early in Earth's history the negative feedback of the carbonate-silicate cycle may have been inoperative or at least significantly less effective than today. This undermines the main negative feedback mechanism proposed to stabilize surface temperature on wet rocky planets for the first billion years or so.

In this project, you will aim to investigate what types of abiotic and biotic weathering might have been active on Earth between 3-4 billion years ago. Students with an interest in programming can use existing planetary evolution and climate models to constraint the relative magnitudes of the different negative feedbacks. Your research will help answer open questions on the role of abiotic and biotically enhanced weathering in a young planet’s habitability.

This project will suit students looking for a 3-6 month project who have an Astronomy or Earth Science background and wish to undertake research in Planetary Sciences.

Over the coming decades, many potentially habitable planets will be discovered, and their atmospheres will be characterised using spectroscopy. To understand if an exo-atmosphere is conducive to life on the surface, one needs to model a range of atmospheric and stellar parameters to estimate the surface conditions. The current generation of photochemistry-climate models which simulate atmospheres given thermodynamic and chemical inputs to make such predictions are slow and resource-intensive.

In this project, you will aim to use existing computer codes and datasets to train a machine-learning algorithm to predict the surface temperature, pressure and flux of atmospheric gases when given the bulk composition of a planetary atmosphere along with other planetary and stellar parameters. Your research will help speed up the analysis, thereby allowing us to understand the range of atmospheric compositions that could be of interest in future remote detection of exoplanetary life.

This project will suit students looking for a 9-12 month project who have a Astronomy or Earth Science background and wish to undertake research in Planetary Science. Some experience in Python programming and data analysis is desirable.

Extant life on Earth shares a common ancestor that probably existed ∼4 billion years ago. The distinct stoichiometry of some elements in each environment and life form could be utilised as a ‘fingerprint’ to probe the association between life and its habitat. The earliest archaea and bacteria, the closest descendants of the Last Universal Common Ancestor (LUCA), were likely to have evolved and diversified around hydrothermal vents. Hydrothermal systems exist in a variety of tectonic settings and each alternative with its unique geochemical properties offers a compelling case as a plausible habitat for LUCA.

In this project, you will aim to analyse the elemental composition of the earliest life forms on Earth and the elemental fingerprints of different hydrothermal settings. As part of your research, you will investigate how the composition of Earth’s oceans, and thus hydrothermal settings have evolved over the last 4 billion years. Your research will help us understand where life might have emerged on Earth, and where it might emerge and evolve on other planets.

This project will suit students looking for a 6-9 month project who have a Biology or Earth Science background and wish to undertake research in Astrobiology or Origin of Life.

While gazing at the Earth from orbit, some astronauts have described a cognitive shift known as the overview effect. Here we describe an analogous biological overview effect produced by looking at the tiny twig of humanity on the tree of life. We describe the increasingly precise phylogenetic tree of all life on Earth and how it shows us our place in nature among the other eukaryotes, metazoa, vertebrates and apes. We discuss problems with this tree including the assumption of sexual isolation, purely vertical gene transmission and the dependence of the epoch of LUCA (Last Universal Common Ancestor) on the completeness of the tree. We compile and present the most concise taxonomic overview of the evolution of our lineage from LUCA to humans. We conclude with a description of how the biological overview effect might help us survive.

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We review planetary habitability. We discuss the physical and biological constraints on the habitability of Earth and other rocky planets. The section on the “physics of habitability” examines the conceptual limitations of circumstellar habitable zones that are conventionally used to discuss habitability. Using the Earth as an example, we discuss how habitability can vary over spatial and temporal scales. In the section on the “biology of habitability,” we describe how life may be the dominant force in keeping a planet habitable over long durations. In the Gaian Bottleneck model, biotic regulation to provide the necessary level of negative feedback, to counter greenhouse and albedo positive feedbacks, is a prerequisite for sustaining habitability. We discuss how the conditions required to start life may be different from conditions required to sustain life and how abiogenesis habitable zones may be short-lived and highlight nuanced views on how planetary habitability evolves over time. We discuss problems associated with defining habitability based on anthropocentric or Earth-specific characterization of life. We suggest how studying the coevolution between life and the environment could offer better insights into the making of a habitable planet.

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Ice-giant-sized planets are the most common type of observed exoplanet, yet the two ice giants in our own solar system (Uranus and Neptune) are the least explored class of planet, having only been observed through ground-based observations and a single flyby each by Voyager 2 approximately 30 years ago. These single flybys were unable to characterize the spatial and temporal variability in ice giant magnetospheres, some of the most odd and intriguing magnetospheres in the solar system. They also offered only limited constraints on the internal structure of ice giants; understanding the internal structure of a planet is important for understanding its formation and evolution. The most recent planetary science Decadal Survey by the U.S. National Academy of Sciences identified the ice giant Uranus as the third highest priority for a Flagship mission in the decade 2013–2022. However, in the event that NASA or another space agency is unable to fly a Flagship-class mission to an ice giant in the next decade, this paper presents a mission concept for a focused, lower cost Uranus orbiter called OCEANUS (Origins and Composition of the Exoplanet Analog Uranus System).

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The Universe is ~13.8 billion years old. The first stars formed ~13.6 billion years ago. During the first ~2 billion years of star formation, the abundance of rock-forming elements was probably not high enough to produce rocky planets massive enough to hold water and atmospheres. Recent evidence suggests that Earth-like planets are common and have been common. The Sun and Earth are 4.6 billion years old. Thus, for 6 billion years preceding the formation of the Earth (from ~11 to ~5 billion years ago), preterrestrial wet rocky Earth-like planets in circumstellar habitable zones formed and evolved. Here, we review the elemental production and fractionation that led from the hot big bang, to the production of elements necessary for rocky planets (e.g., Fe, O, Si, Mg) and the production of elements necessary for life as we know it (e.g., C, H, O, N). Thus, we trace the potentially universal evolution from physics to chemistry to biochemistry and life. We argue that the elements, molecules, rocky planets, and geochemistry produced by these processes are fundamental requirements for life. As far as the fundamental geochemistry and biochemistry of life is concerned, there does not seem to be anything special about the Earth compared to other wet rocky planets. Thus, it is very plausible that some kind of life may have emerged many billions of years before the emergence of life on Earth. As we learn more about the geochemistry of the early Earth and the origin of the first life on Earth, we are learning about the life which probably emerged before the existence of our Solar System.

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The break-up of the supercontinent Pangaea around 180 Ma has left its imprint on the global distribution of species and resulted in vicariance-driven speciation. Here, we test the idea that the molecular clock dates, for the divergences of species whose geographical ranges were divided, should agree with the palaeomagnetic dates for the continental separations. Our analysis of recently available phylogenetic divergence dates of 42 pairs of vertebrate taxa, selected for their reduced ability to disperse, demonstrates that the divergence dates in phylogenetic trees of continent-bound terrestrial and freshwater vertebrates are consistent with the palaeomagnetic dates of continental separation.

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The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. Here, we present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.

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For life-forms like us, the most important feature of Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. During the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabited regions on Earth tell us that temperature and the presence of water are the main constraints that can be used in a habitability classification scheme for rocky planets. Our compilation and review of recent exoplanet detections suggests that the fraction of stars with planets is ∼100%, and that the fraction with rocky planets may be comparably large. We review extensions to the circumstellar habitable zone (HZ), including an abiogenesis habitable zone and the galactic habitable zone.

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We review the most fundamental features common to all terrestrial life. We argue that the ubiquity of these features makes them the best candidates for being features of extraterrestrial life. Other frequently espoused candidates are less secure because they are based on subjective notions of universal fitness, not on features common to all terrestrial life. For example, major transitions in the evolutionary pathway that led to Homo sapiens are sometimes considered to be fundamental transitions in the evolution of all life. However, these “major transitions” are largely arbitrary because a series of different major transitions can be identified along the evolutionary pathway to any extant species.

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As we begin to understand the origin and evolution of life on Earth and investigate the possibility of extraterrestrial life, the need to scientifically approach fundamental questionssuch as ‘What is Life ?’ increases. In beginning to answer such questions we can look at the ingredients of life on Earth. Here we present an overview of our understanding of the composition of life on Earth. At the level of chemical elements, the major ingredients are carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus along with trace amounts of elements like sodium, potassium, iron and copper. Here we present the correlation between the elemental composition of life (humans and bacteria), the Sun and sea water. Some elements like carbon, nitrogen and phosphorus are more abundant in life than in sea water, while others like chlorine and sodium are more abundant in sea water than in life. We quantify differences in elemental abundances in life, relative to sea water and attempt to interpret them in terms of chemical constraints on metabolic activities and harnessing energy. We discuss how future investigations could further our understanding of the origins and evolution of life on Earth.

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