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This chapter reviews the discussions in the preceding chapters and presents some concluding thoughts from the author. The biology of soil is of fundamental importance to the sustainability of life on Earth. Not only will new insights into the biology of soil improve our understanding of how managed and natural ecosystems are structured and function, it will better enable humans to predict the effects on ecosystems of human-induced global changes and enhance our ability to restore degraded ecosystems. However, soil remains the least understood, and perhaps most abused, habitat on Earth.

This chapter describes soil conditions that support grasslands in California and discusses how land use history in California has influenced soil biology and soil organic C cycling. It begins by describing California soils that support grasslands and considers some of the soil factors that influence the potential vs. actual distribution of grasslands in the state. Then, some examples of relationships between soil organic C cycling and the composition of microbial and plant communities are described after conversions from grasslands to cultivated agriculture, and vice versa. Recent research that utilizes agricultural practices to restore native perennial grasslands from annual grasslands is also included. The chapter concludes with some implications of future land use change on grassland soils and management.

This chapter provides an overview of the three chapters in Section 1. Chapter 1.1 considers the soil as a habitat. Chapter 1.2 reviews the levels of biodiversity that occur belowground. Chapter 1.3 considers how the soil biota actually delivers ecosystem services. It also explores the contrasting ‘soil biogeochemistry’ and ‘soil biology’ perspectives of how ecosystems function, and reviews the functional group concept.

This chapter discusses the last book that Charles Darwin wrote before his death that has been celebrated in the fields of soil biology and earthworm ecology as a landmark contribution. It is argued here that the relative neglect of Darwin’s “worm book” stems from his investigating a previously considered unorthodox topic: the formative impact of organisms on their physical, chemical, and biotic surroundings. Darwin’s understanding of the global effects of earthworms is presented here, after which it is shown that his conceptual and empirical framework is consonant with geophysiology—the science of the Earth as a living system. The chapter concludes with a discussion of the implications of Darwin’s argument in the contemporary context of global environmental degradation.