The current worldbuilding project I have is going to be detailed - very detailed.

It's about the life of an alien planet called Nemo 4, and I want to chronicle the evolutionary history of that life, from the arrival of unicellular organisms on a comet to its now flourishing ecosystems.

But evolutionary history is closely tied with geographic history - continents joining up causes fauna exchanges, and animals evolve various adaptations to certain climates which are a product of geography.

So, I have a map of all the current continents, and the tectonic plates and which way they're moving. So, how can I work backwards from this map to know what my world looked like 10 million years ago, 100 million years ago, even a billion years ago?

I can presume that it is dependent on; a) tectonic plates, b) the speed at which they move, and c) sea level, which is affected by temperature.

Obviously, these things are largely based on sporadic, unpredictable events, but is there any way that I can plausibly go about constructing a timeline of the lay of the land of my planet?

If you think this is broad, off-topic, unclear etc. please say so, as it's a lot more helpful than doing it without saying anything.

  • $\begingroup$ I think you could have a quick look at how Earth looked at each geological eon and make your planet go through something similar on each stage. For example, you planet will have gone through a hadean phase at some point. $\endgroup$ Jun 25, 2018 at 15:43
  • 2
    $\begingroup$ Um you get a degree in Earth Science and then it's still guesswork and a lot of "what would be convenient here". $\endgroup$
    – Ash
    Jun 25, 2018 at 15:45
  • $\begingroup$ Current landforms are best for recent history, As you go farther back, current landforms tell an incomplete story. Example: The few remaining surface landforms around the Chicxulub Crater were insufficient to indicate that a major mass-extinction event took place there...and 65 million years is recent geologic history. $\endgroup$
    – user535733
    Jun 25, 2018 at 17:10
  • $\begingroup$ I'm afraid that most of this is just going to be things happening the eay you want them to happen, so you'll have to map out what you want and then tweak it. The planet's tectonic history is going to be written in the rocks. Have you placed your ancient cratons, mountain ranges, thrust zones and metamorphic belts, seamounts with coral reefs, volcanoes, flood basalts, sedimentary basins from ancient shallow oceans and other sedimentary layers? All of these geological cues are going to tell your planets tectonic history. Which direction you start from is up to you. $\endgroup$
    – Spencer
    Jun 25, 2018 at 17:53

2 Answers 2


If you want to go backward in your geological history, use these known phenomena:

  • Rivers flow from the top of the mountains to the sea, while doing so they carve V shaped valleys in the regions they cross
  • Glaciers do the same, but they carve U shaped valleys, and deposit particular materials where they melt (moraine)
  • Mountains raise either next to places where plaques are colliding or as a consequence on volcanic activity.
  • Sedimentary rocks form in the sea, with an higher amount close to rivers mouths. Also lakes or lagoons form sedimentary rocks.

For example it is known it is known that the Amazon River changed its flow along its history:

The proto-Amazon during the Cretaceous flowed west, as part of a proto-Amazon-Congo river system, from the interior of present-day Africa when the continents were connected, forming western Gondwana. Fifteen million years ago, the main tectonic uplift phase of the Andean chain started. This tectonic movement is caused by the subduction of the Nazca Plate underneath the South American Plate. The rise of the Andes and the linkage of the Brazilian and Guyana bedrock shields, blocked the river and caused the Amazon Basin to become a vast inland sea. Gradually, this inland sea became a massive swampy, freshwater lake and the marine inhabitants adapted to life in freshwater. For example, over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon.


Tectonics backwards:

Since you already have your continents and tectonics plates, you can create story backward following these principles:
1. Define the type of collision between your current plates, if it is a subduction, then one plate is dissapearing below the other (this usually does not happen, because subduction is between a sea plate and a continent plate), example: Nazca plate with South American plate. If the collision is straight, then both plates reduce their surface and increase their height, example: India and Asia plates in the Himalayas. If the collision is lateral, no important change on plates happens, example: Saint Andreas in California.
2. Once you have defined the collision, then you need to define the rifts, this is the place were the plates form and separate each other. Example: middle of Atlantic. Some rifts can be inside a continent.
3. Some plates might do not have a rift or a subduction, they just float around.
4. Once you have defined these two zones (rifts and collisions), where a plate is created and where it ends, then the moving backwards is easy, you just need to define the speed of each plate moving towards the rift and against the contact with other plates. Whenever two plates separate each other, a mountain is lost and maybe a sea appears.

While stronger is the collision, faster a mountain grows. Near the Ecuator, less erosion in mountains you'll have. Zones far away of collision between plates are usually flat. Coriolis effect create currents in the ocean that are clockwise in the north, and counterclockwise in the south. Hot water and big mountains increase rainfall.

But, is easier to go forward instead of backwards. Because rifts follow certain rules that are hard to fulfill if you go backwards, specially when you have to deal with the rule of triple junction.


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