Natural Environmental Change: The Last 3 Million Years

By A. M. Mannion | Go to book overview

Introduction

1.1

Preamble

The Earth has never been characterised by a constant, static environment; environmental change has been the norm rather than a rarity throughout the c. 5000×106 years of Earth history. On both a temporal and spatial basis, the rate of change has varied, with long periods of gradual and subtle transformation punctuated by major upheavals. The study of Earth history has developed in a similar way, with periods of consolidation following the acceptance of major theories.

Environmental change has also been rhythmical in character because of the influence of regular fluctuations such as the revolution of the Moon around the Earth and the revolution of the Earth around the Sun. Such fluctuations influence the pattern of tidal frequency and seasonality. The Earth experiences additional oscillations which are cyclical, e.g. the recurrence of phenomena such as mountain building or climatic change generated by the periodicity of the Earth’s orbit around the Sun (the Milankovitch hypothesis—see Section 2.4), which have occurred throughout geological time.

These and all other aspects of Earth history have influenced, and been influenced by, life. The manifestation of this relationship is the operation of biogeochemical cycles whereby, as is implied by the term, chemical exchanges occur between the compartments of the Earth (the lithosphere, hydrosphere, biosphere and atmosphere, Figure 1.1) and are mediated by living organisms that comprise the Earth’s biota. Consequently, environmental change can be expressed in terms of adjustments in global biogeochemical cycles. Such changes have been ultimately associated with climatic change throughout Earth history, especially in relation to the carbon, nitrogen and sulphur cycles.

Only in the last 200 years has the idea of a dynamic Earth been in vogue. Theories concerning plate tectonics, the

Figure 1.1 The relationships between the lithosphere, hydrosphere. atmosphere and biosphere

-1-

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