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It may seem that the earth is pretty stable. You can always count on the mountains being there when you look for them. But the Earth is a dynamic place. Volcanoes, floods, landslides, and earthquakes all change the landscape in ways we can see quickly. What we don’t typically see is that if we expand these processes over long periods of time, those same processes alter the landscape far beyond our experiences. The surface of the Earth is covered in a crust broken up into numerous plates, which are constantly shifting and moving. The plates only move between 2.5 – 15 cm/year (the previous link contains information on how this is measured and provides activities for teachers for use in the classroom), but add this up over millions of years and the Earth looks quite different. Add into this mountain-building and erosion wearing down the mountains and you get radically different geographies for the planet.
So what did the Earth look like in the past? There are two excellent sources providing maps of the planet through time. The first is the PALEOMAP Project, by Dr. Christopher Scotese. On this website, you will find maps ranging from 650 million years ago to the modern day and even into the future. There are 3D animated globes and interactive maps. He includes a methods section for how the maps wer put together and a list of references and publications. There is also a climate history section providing brief descriptions of the climate at various points in time. For teachers, there are several educational resources available, some of which are free, but others are available for a fee. There is even an app for the iPhone/iPad. It is not available yet for either android or Windows, but that has been admirably taken care of by the Howard Hughes Medical Institute with their Earthviewer app and they have done a wonderful job. the app is fully interactive, allowing easy scrolling through time and full rotation of the globe. You can also track atmospheric oxygen and carbon dioxide, day length, important fossils, biological and geological events, and major meteor impacts. The app even provides a bibliography of their source material. In addition to the maps from Dr. Scotese, the app extends the timeline back to 4.5 billion years (although this extension is obviously not nearly as detailed as the Scotese maps due to the greatly extended time and the greatly decreased amount of available data). All in all, a great app, also reviewed by the NSTA.
The second site that will be of interest is the Library of Paleogeography run by Dr. Ron Blakely. These maps cover approximately the same time frame as those provided by Dr. Scotese and are not animated. However, Dr. Blakely provides maps in different projections and provides regional coverage beyond that of global maps. So if you are specifically interested in paleogeographic maps of North America and Europe, this is an excellent resource.
A third site also provides paleogeographic maps which are very useful. In this case, the maps are secondary to the main purpose of mapping fossil locations. The Paleobiology Database contains records of fossil locations that have been published in the primary literature. One can perform a search by organism or group, country, rock unit or type, time interval, paleoenvironment, or publication. The results from the search are mapped onto global maps based on the PALEMAP Project.
All of these sources are available to the public and are used by professional researchers. Therefore, one can safely assume they represent accurate assessments of current, generally accepted thoughts on our Earth through time. You may notice that maps from Scotese and Blakely may not completely agree on all aspects. This is because it is very hard to piece together all the evidence and trace the movements of the continents backwards through time. Often, the data is incomplete and they have to make judgment calls based on the available evidence. Not everyone makes the same choices. This is true even for maps of current geography and is even more so for paleogeography. As we get more data and better techniques, those disagreements become fewer and fewer, but there is still much work to be done, so these maps can and will most likely be refined in the future to reflect new research.