Our chief aim in writing this book is to interpret, decipher, and describe the complex history of our planet over the most recent half billion years and the processes through which it has changed, and to compile maps of both the distribution of the many tectonic plates through that time, and also show where the lands and seas were situated over that long period. As is usual with narration, we start at the beginning and carry on progressively through time as it elapsed, but the result of that natural sequence is to commence by discussing the periods over which we have the fewest quantitative constraints on Earth’s old geography, and thus our geographical reconstructions gradually become more accurate as time continued on up to the present day.
After a brief introduction (Chapter 1) we describe the varied and often independent methods (Chapter 2) that we have used to reconstruct old lands and seas. In Chapter 3, we list all the unit areas among the many which make up our planet and which are the ones we have used in the construction of our kinematic computer-generated palaeogeographical maps through time, with a very brief sketch of their geological constitutions. Each of those units, which vary in size from large continents to small terranes, can be downloaded digitally.
The history of the Earth falls naturally into two very unequal divisions: the Precambrian, in which there are no fossils of use in determining the positions of the former continents, and that, including the origin of the planet, is only summarised here in Chapter 4. The Precambrian was followed by the Phanerozoic at 541 million years ago (Ma), and the latter started with the Palaeozoic, from which there is no old in-situ ocean crust preserved, but when the biota was distributed in faunal and floral provinces which are very relevant in assessing oceanic separations in the absence of much useful geophysical data (apart from palaeomagnetism). The boundary between the Palaeozoic and the overlying Mesozoic to the present day was at 252 Ma, after which the ocean-floor magnetic stripes and other useful geophysical data become progressively more abundant and objective, but when the biota, although interesting in its evolutionary development, is again of no primary help in deciphering the palaeogeography. Thus there are separate chapters here for each of the main geological systemic periods from the Cambrian to the Quaternary (Chapters 5 to 15).
Over the past billion years, our planet’s climate has fluctuated wildly between hot and cold temperatures, some so extreme that any life has been scarcely possible. Thus, as well as mentioning those climates during the individual periods in Chapters 4 to 15, the final Chapter 16 brings together the many factors which affect and support the Earth’s climate, and also describes how and why that climate has changed so much during the half billion years and how it has come to be what it is today.