Milankovitch and Tidal Cycle History (MATCH)

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The Apollo 11 moon landing on July 20 1969, was a major achievement in the history of human civilization. The rock samples brought back showed that the moon was 4.5 billion years old, and so must have formed only 200 million years or so after Earth formed. The mirrors left on the surface of the moon during the Apollo missions allowed us to very accurately measure the Earth-moon separation, and the rate at which the Earth and the Moon are moving away from each other or receding. This recession rate is estimated to be 3.8 cm/year. However, if this recession rate was constant in time, the moon would only be 1.5 billion years old, otherwise it would have been torn apart by the Earth's gravitational field. Here lies an obvious paradox: the age of the moon and the present-day recession rate do not add up!The reason the moon is receding is tidal friction: the loss of tidal energy into the ocean is gradually slowing the Earth's rotation rate and pushing the moon away from the Earth. If tidal friction is weak, the moon will recede more slowly, whilst if tidal dissipation is large, the moon will recede more quickly. However, we currently have very few reliable estimates of the dissipation of tidal energy over the history of Earth. Furthermore, these are restricted to a few time slices over the more recent Earth history (the past 250 million years). These estimates indicate that the tidal dissipation rate has not been constant over time. Work by team members have predicted the existence of a "super tidal cycle" - with a period of 400 million years - in which the tidal dissipation varies by a factor of four and is associated with continental drift.The dawn of supercomputers has facilitated the development of high-accuracy global tidal models, which allow us to simulate the tidal dissipation rates in Earth's past. From the modelled dissipation, we can compute the past lunar recession rates for a large number of time slices. The recession rates from the model will be constrained for a few periods using data from bore holes. In bore holes there are signals of long-term climate cycles laid down in the sediments, but to analyse them you need the lunar recession rate. Using a new approach developed by the team, we will analyse data from a number of holes and provide a tool to confirm the model results. The novelty of our approach being that it does not assume a constant recession rate and so allows us to achieve a step change in our understanding of the evolution of the tides globally and quantify the evolution of Earth-Moon separation on geological time-scales.Achieving this aim will allow us to better predict the evolution of the Earth-moon system by providing detailed estimates of the lunar recession rate over the past 600 million years. This has implications for ocean tides in the Earth system, for example how the tide provides energy for stirring the ocean and thus sustaining biological production and influencing the climate-controlling global ocean circulation patterns. The project results will also be important for any investigation in need of lunar recession or tidal dissipation rates, for example investigations of past climate cycles, sediment laminations, and for simulations of past climates.