Best rock for radiometric dating
Fluctuations, or "anomalies", in the intensity of the magnetic field, occur at the boundaries between normally magnetized sea floor, and sea floor magnetized in the "reverse" direction.The age of these linear magnetic anomalies can be determined using fossil evidence and radiometric age determinations.
What has changed, is the shape and the distribution of continents across the globe.Less extensive mountains can also form when continents rift apart (e.g.East African Rift), or where hot spots form volcanic uplifts.In most cases mountain ranges take 10's of millions of years to form, and depending on the climate, may last for 100's of millions of years.Though the Appalachian mountains of the eastern United States were formed over 300 million years ago, due to the collision of North America and western Africa, remnants of this collisional mountain belt still reach heights of over than 2000 meters.The second goal is to illustrate the changing distribution of mountains, lowlands, shallow seas, and deep ocean basins through time.
The past positions of the continents can be determined using the following five lines of evidence: paleomagnetism, linear magnetic anomalies, paleobiogeography, paleoclimatology, and geologic history.
The similarity or dissimilarity of faunas and floras on different continents can be used to estimate their geographic proximity.
In addition, the evolutionary history of groups of plants and animals on different continents can reveal when these continents were connected or isolated from each other.
The ocean basins, on the other hand, are all less than 150 million years old.
Oceanic lithosphere, because it is more dense is continually recylced back into the interior of the Earth.
The ancient distribution of these, and other, rock types can tell us how the global climate has changed through time and how the continents have travelled across climatic belts.