The question of whether Mars could have supported life has driven intensive exploration of the planet's surface through satellite and robotic missions. Complementary research has focused on identifying and understanding meteorites from Mars, which offer the only direct samples of the crust available to science. Together, these studies have not only sought signs of extraterrestrial life and habitable environments, but tried to understand how the planet has changed through time: from an ancient world of oceans and landforms remarkably familiar to Earth, to the cold, dry, barren planet that we see today. Why Mars has followed a dramatically different path to Earth is a major issue in our understanding of terrestrial planet evolution. How has Mars lost heat? Has volcanism and volcanic outgassing changed through time? Is volcanism and seismic activity ongoing? How has impact cratering shaped the planet through time? It has become clear that much of the surface of Mars is very ancient, and that its rocks retain direct evidence of the planet's separation into a crust and mantle. As a result, volcanism is thought to be driven by mantle plumes, rather by tectonic forces at plate boundaries as on Earth, and to have reduced rapidly in intensity to a minimum as the planet has cooled. This relatively simple geological model compared to the Earth suggests declining rates of exchange between the surface, atmosphere and interior through time, including the cycling of potential nutrients, heat loss and volcanism. This view has been challenged by recent evidence for considerable diversity in volcanic and sedimentary rocks and processes on Mars. However, new understanding of the planet is hindered by a mismatch between Martian meteorites and rock types seen on the surface, as well as a lack of reliable age information that can be used to test how the crust, mantle and atmosphere have evolved and interacted through time. Addressing these issues is a primary aim of ongoing and new Mars exploration missions, including NASA InSight and Mars 2020 and the ESA ExoMars Rover, and also requires resolution of conundrums in the Martian meteorite collection. The UoP2 Mars Consortium brings together internationally leading expertise in Martian meteorites, radiometric dating and planetary geology to address these challenges. Two related projects will capitalize on conceptual and analytical advances in the laboratory analysis of planetary materials led by the applicants, as well as the rapidly growing inventory of Martian meteorites in collections around the world, to generate new datasets and knowledge. Project 1, entitled "Secular evolution of Martian magmatism" focuses on placing robust new age constraints on Martian volcanic processes. Previously, this has been very difficult because the samples have experience extreme compression and heating during impact events, which disturb the isotopic systems used for dating. We will overcome this using advances led by Darling in identifying nanoscale deformation features in dateable crystals that can be avoided or targeted for radiometric dating using the latest techniques in mass spectrometry. Project 2, entitled 'Martian Breccias; the missing link in the search for Meteorite Source Regions on Mars?' focuses on linking the meteoritic and remote sensing records to build a more complete picture of the Martian crust. This will be achieved by resolving the origin and spectral signature of newly discovered brecciated rocks that offer uniquely broad sampling of Martian crustal rocks through clasts of different origin, in combination with new and compiled data on the mineralogy and geochemistry for other Martian meteorite groupings. The results will lead to new holistic models for Martian geological evolution. This new knowledge will help to address one of the four Science Challenges of the STFC Science Roadmap1: How do stars and planetary systems develop and is life unique to our planet?

This study will test the hypothesis that wear patterns on fossil conodont teeth differ according to whether species lived on the sea floor or above it. If wear does differ, as it does in fish teeth, this will provide a new way of increasing the reliability of conodonts in geological and deep-time environmental analysis. Conodonts were small, eel-like primitive fishes. They have been extinct since the end of the Triassic, but the 300 million year record of their microscopic fossil teeth is exceptionally complete, and they are easy to obtain in large numbers by dissolving limestone in weak acid. Consequently, conodonts are among the most important tools for geological dating - determining when rocks were laid down and when geological events occurred. They are also increasingly important tools for investigating the palaeoclimate, palaeotemperature and palaeooceanography of geological periods in deep time, studies which are important for understanding the context of current climate change. For example, investigations of the oxygen isotopes in conodont teeth are providing new insights into glaciations, sea level and sea temperature hundreds of millions of years ago. Conodonts are particularly suited to such studies because the structure and calcium phosphate composition of their tooth crown maximises the chances that the chemical signatures recorded in the teeth reflect ocean conditions at the time the animal was alive, and minimises changes caused by the process of fossilization. Recent work indicates that isotopic analyses based on conodont crown tissue give more reliable results than analyses of any other fossil teeth or shells of comparable age. Realising the full potential of conodonts, however, requires that we can constrain their ecology and mode of life. Differentiating between benthic taxa, which lived on the sea floor, and pelagic taxa, which lived away from the sea floor and in surface waters, is particularly important. The best taxa for geological dating are pelagic, because pelagic taxa have broader (potentially global) distributions. They also disperse more rapidly, so the time at which a newly evolved pelagic species first appears in the fossil record in different locations is more likely to be synchronous (important for establishing the age equivalence of rock sequences). Analyses that interpret shifts in the chemical composition of conodont tooth crowns in terms of temperature or sea level must exclude the possibility that differences between samples reflect differences in the depth habitat at which the sampled conodont species lived (deeper water is cooler). Unfortunately, the mode of life of conodonts is poorly constrained, and this causes problems. We know that they were active swimming animals that ranged from shallow nearshore through to deep ocean environments, but determining whether a particular species occupied a benthic or a pelagic niche is difficult. Current methods, based on hypothetical distributions of conodonts along depth gradients, are rather crude and generally unreliable. This proposal aims to develop a new approach to constraining the depth habitats of conodont taxa. Recent work led by the investigator discovered that patterns of tooth wear in benthic feeding fish differ from those of pelagic feeding fish and can be used to study changes in feeding in fossil fish. Does the same apply to conodonts? In order to find out we will conduct the first systematic analysis of conodont tooth wear and test the hypothesis that pelagic feeding and benthic feeding species exhibit different wear patterns. This will be based on microscopic investigation of hundreds of conodont teeth and detailed statistical analysis of the patterns of wear preserved on their surfaces. These teeth will be taken from samples where, unlike most conodonts, the palaeoecology of the species is well constrained. If differences are detected, isotopic analysis will provide independent data concerning temperature/depth habitat.

The aims of this project are simple. By rotting velvet worms (onychophorans) under controlled conditions we will generate the data required to start correctly interpreting the fossil record of lobopodians. Accurate placement of lobopodians in the Tree of Life has the potential to resolve a major evolutionary problem: the origin of the arthropods. Arthropods are arguably the most successful animals on Earth: more diverse and abundant than any other group, they are important and familiar to everyone. Yet the identity of the arthropods' nearest living relatives, and the details of arthropod origins and early evolution remain unclear. In contrast to arthropods, onychophorans are both obscure and enigmatic. With their fat legs and body annulations they resemble a conga-line of overweight Michelin-men. A recent popular account of animal relationships noted that 'no group has prompted more zoological debate' (Tudge 2000, The Variety of Life) - exactly where onychophorans sit in the Tree of Life remains controversial. Surprisingly, answering the question of onychophoran relationships holds the key to unlocking the evolutionary emergence of the arthropods, and this is where fossil lobopodians have a major role to play. These extinct, soft-bodied organisms (almost all of Cambrian age) share a number of important anatomical features with onychophorans, but recent evolutionary analyses suggest that fossil lobopodians include the ancestors of arthropods, of onychophorans, and of panarthropods (the larger group to which both onychophorans & arthropods belong). Consequently, finding the correct places for fossil lobopodians in the Tree of Life has the potential to reveal the sequence in which important characteristics of arthropods and onychophorans were acquired. If lobopodian branches do fill the gap between living onychophorans and arthropods, we may be able to resolve relationships between the major arthropod branches. This potential can only be realised with correct placement of lobopodians, and this requires new information about how they decayed. Much of the current disagreement over the placement of lobopodians arises because we don't understand how the process of decay affected their bodies prior to fossilization. Studies of other organisms show that decay rapidly alters the appearance of important anatomical features. As soft tissues rot and collapse the shape and juxtaposition of body parts - crucial criteria for anatomical comparison - change significantly. Other features rot away completely. We need new data so that these changes, which will have affected all fossil lobopodians to some degree, can be taken into account when interpreting their anatomy. We will employ a new approach to the experimental study of how animals decay, recently developed in our lab. We will rot onychophorans under controlled lab conditions and carefully record their important anatomical features (many of which they share with fossil lobopodians) at timed intervals as they decompose. From this we will determine the rate and sequence of decay of features; when and how their juxtaposition, shape and appearance change. This will allow us to establish criteria for the recognition of decay-transformed features in fossil lobopodians and reassess the anatomy and evolutionary relationships of these controversial animals (including exceptionally well-preserved new material). It will also allow us to further test a hypothesis developed from our ongoing decay experiments: that the decay of evolutionarily important anatomical features of soft bodied animals is not random - features that are most useful for recognizing evolutionary relationships are the most likely to decay rapidly. If this pattern is widespread it is an important yet previously unrecognised bias in reconstructing the evolutionary relationships of fossils.