Free energy sources in the very long run

Judson - 2017 - The energy expansions of evolution

The history of the life–Earth system can be divided into five ‘energetic’ epochs, each featuring the evolution of life forms that can exploit a new source of energy. These sources are: geochemical energy, sunlight, oxygen, flesh and fire. The first two were present at the start, but oxygen, flesh and fire are all consequences of evolutionary events. Since no category of energy source has disappeared, this has, over time, resulted in an expanding realm of the sources of energy available to living organisms and a concomitant increase in the diversity and complexity of ecosystems. These energy expansions have also mediated the transformation of key aspects of the planetary environment, which have in turn mediated the future course of evolutionary change. Using energy as a lens thus illuminates patterns in the entwined histories of life and Earth, and may also provide a framework for considering the potential trajectories of life–planet systems elsewhere. 

Free energy is a universal requirement for life. It drives mechanical motion and chemical reactions—which in biology can change a cell or an organism. Over the course of Earth history, the harnessing of free energy by organisms has had a dramatic impact on the planetary environment. Yet the variety of free-energy sources available to living organisms has expanded over time. These expansions are consequences of events in the evolution of life, and they have mediated the transformation of the planet from an anoxic world that could support only microbial life, to one that boasts the rich geology and diversity of life present today. Here, I review these energy expansions, discuss how they map onto the biological and geological development of Earth, and consider what this could mean for the trajectories of life–planet systems elsewhere.

Worth reading in its entirety for the log-timescale perspective on energy budgets alone, but also as a fantastic piece of science writing and communication. "Of all the planets and moons in the Solar System, Earth is the only one to have fire..."

Human socio-economics predict elephant population better than elephant habitat

Understanding spatial differences in African elephant densities and occurrence, a continent-wide analysis
Willem F. de Boer, Frank van Langevelde, Herbert H.T. Prins, Peter C. de Ruiter, Julian Blanc, Marc J.P. Vis, Kevin J. Gaston, Iain Douglas Hamilton

The densities and survival of many wild animals are presently at risk. Crucial for improving conservation actions is an understanding on a large scale of the relative importance of human and ecological factors in determining the distribution and densities of species. However, even for such charismatic species as the African elephant (Loxodonta africana), spatially explicit, large-scale analyses are lacking, although various local-scale studies are available. Here we show through continent-scale analysis that ecological factors, such as food availability, are correlated with the presence of elephants, but human factors are better pre- dictors of elephant population densities where elephants are present. These densities strongly correlate with conservation policy, literacy rate, corruption and economic welfare, and associate less with the availability of food or water for these animals. Our results suggest that conservation strategies should be organized in a socioeconomic context. The successful conservation of large animal species could depend more on good human education, greater literacy, good governance, and less corruption, than merely setting aside areas for conservation.

h/t Nitin