The nature of the Earth prior to the oldest known rock record: the Hadean Earth

Abstract

Statements about the Earth's history prior to 3.8 Ga ago, the age of the oldest rock sequence now known on Earth, are based on indirect evidence (such as that derived from meteorites and lunar samples) and on plausibility arguments, the persuasiveness of which often depend more on the eloquence of their advocates than on the weight of relevant data. Such statements, however, are of profound importance as they relate to one of the central issues of this volume - the origin of biologic systems (see Chapter 4) - an event that may well have occurred during the pre-3.8-Ga-old "Hadean" segment of Earth history. Yet understanding of the Hadean Earth is far from complete; in particular. and because of the paucity of directly relevant data, theorists dealing with the problem are obliged to work with "models," constructs that can be no better than the input assumptions. New data or interpretations can cause these models to be discarded or recast. The discussion presented in this chapter should be seen in this light: basic physical principles need to be understood, but for the present, detailed scenarios or predictions based upon them are best regarded as "convenient fictions," worthy of discussion but not enshrinement.

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