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Giant ore deposits are priority targets for mining companies. A review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency.
About 4 billion years ago, the terrestrial planets were bombarded by asteroids following an orbital shake-up of the outer Solar System. Lunar samples, planetary cratering records and dynamical models piece together an increasingly coherent view of this bombardment interval.
A 500,000-year-long period of warmth in the middle Eocene was marked by high atmospheric carbon dioxide concentrations and prolonged dissolution of carbonate in the deep oceans. Numerical simulations attempting to capture these features identify gaps in our understanding of the causes of this and similar perturbations.
Temperature change over the past 2,000 years has shown pronounced regional variability. An assessment of all available continental temperature reconstructions shows a clear twentieth century warming trend, but no evidence of a coherent Little Ice Age or Medieval Warm Period.
