I was watching a video about the Permian period of Earth’s history (*watch out for those Dinogorgans!)* and they talked about where various animals lived across the Pangea supercontinent.
It got me thinking – how do we know exactly what Pangea looked like? How do we know that, for example, Iran and Tibet were islands way back then? Is there enough geological evidence to be super confident about the make up of the super continent? Or is sort of a “best guess”?
In: Planetary Science
Geological features! Rocks are not identical, there are lots of different types of rock, and lots of variations even within a given type of rock. So, if you find an unusual type of rock in two different places, its likely that those places actually used to be closer together sometime in the past. A classic example of this is that the Appalachian mountains in the USA and the Scottish Highlands are actually part of the same ancient mountain range, identifiable by unique and distinct rock formations and types that are present in both locations, even though they are now separated by an entire ocean!
It really was very much a very large, complicated puzzle. And I don’t just mean by fitting the continents together. There are a lot of subtle details in rocks, such as their texture and chemistry, that can tell us about the conditions they formed under. Then you consider those details in the context of other scientific findings. Bit by bit, through the work of thousands of scientists, the puzzle takes shape.
If we take your example of how we know Iran and Tibet were islands: in the Permian these lands were part of a continental fragment that scientists call Cimmeria. We know it wasn’t originally a part of Asia because there are old faults and folds and rocks metamorphosed by heat and pressure, all pointing to an ancient collision between land masses. We can also match some of the rocks in Cimmeria to rocks in parts of Australia and other continents, so we know it rifted away from the southern continent of Gondwana. Sedimentary rocks and the fossils they contain can tell us if an area was underwater. For example shale is a fine-grained rock formed from mud, usually under the sea. It requires calm water, since fine sediment can’t settle if the water is stirred by waves or strong currents. The chemistry and fossils give us information on the climate. Some rocks even preserve a magnetic impression left by Earth’s magnetic field. All this together can tell us where the rock was when it formed.
Latest Answers