The Earth

USEFULNESS OF THE EARTH’S HISTORY

The Earth’s history is in itself a very interesting research theme, but it is also essential if we want to understand fully what is happening in the present Earth. For example, let us consider the Earth’s magnetism. As said in earlier chapters, the fluid motion within the metallic core acts as a generator and gives rise to the geomagnetic field. Studying magnetohydrodynamics in the present-day core alone, however, will not lead to a total understanding of the origin of the geomagnetic field, because many of its characteristics, such as the reversals of its magnetic polarity, need to be examined on a time scale of tens of millions of years. In order to understand why and how the geomagnetic field emerged, we need to understand not only the evolution of the core, but also the evolution of other components in the Earth system. In fact, most topics in Earth sciences can be understood more deeply in the context of the evolving Earth. The Earth is steadily cooling down with declining internal heat production, and everything is changing with time, albeit very slowly.

Studying the Earth’s history also provides the most effective means to forecast the fate of this planet. We cannot, of course, predict everything by studying the past. For example, research into the Earth’s history does not give us a particularly useful way to predict the timing of major earthquakes, which may occur anytime. Also, studying the past does not instantly provide a clue to what we should do for the future. History does not repeat itself in exactly the same way. A careful reconstruction of what happened in the past must be followed by a theoretical study to understand why and how exactly it happened. Without this combination of observations and theory, we cannot extrapolate our understanding to the future Earth with confidence.