How to explain lack of fosil fuels on an Earth-like exoplanet?

Question

Planet - habitable, tidally locked planet orbitting red dwarf.

Aim: a realistic answer (neither involving handwavium nor aliens that used it all) why a virgin planet that already experienced a while ago its great oxygenation event, has practically no easily accessible (by standards of early XXIst century technology) fossil fuels sources. I mean especially oil and natural gas, however lack of coal would also be beneficial.

Thus the questions:

1) How to explain that?

2) What fossil fuel sources would still be accessible anyway?

My tries:

1a) Maybe continental drift that moved continent with fossil fuels sources in the coldest regions under a few km of ice, and moved those that were covered with ice to the light side of the planet)

1b) Really deep ocean - makes any drilling extra hard

2) Presumably some bog would be unavoidable. I have no idea about gas and oil. To be safe I thought about putting them in tiny quantities that do not justify drilling.

Answer 1

Mass extinctions have nothing to do with large oil deposits, unlike at least 2 answers have said it does.

Oil accumulates largely due to vegetation and aquatic life forms dying and their carbon/hydrogen remains are locked away under some barrier over very long periods of time...

If scientists came upon a planet that had little or no fossil fuels they would likely think 1 of 3 things.

1. Life on this planet is young, thus not enough time to accumulate.

2. The processes that create oil were somehow being blocked or retarded. For example, if the vegetation on the planet didn't lose it's leaves ever this would greatly reduce the speed that oil was being produced, whether was a result of it's orbit causing summer to be very long or the plantlife just didn't develop that way.

3. You're dealing with a planet that had alien sentient life and they used it all up and then something happened to them, either died out, or left, or something.

The first hypothesis is relatively easy to check. Just determine the age of the star and the planet and such and we can come up with an estimate of how old life is based on that.

The second hypothesis should be easy too. Just look monitor the vegetation for a few years.

The third hypothesis... You should be able to find some ruins somewhere, or an artifact that says don't touch if they restored the environment.

If you couldn't find or come to any conclusion within a few years then maybe you got a worthwhile mystery that I can't think up any explanations for.

Answer 2

You have a slight technical hitch with your planet, in that the mechanism for getting lots of free oxygen into the atmosphere is the long-term burial of organic carbon. Basically, if you bury carbon in the form of trees and dead ocean life in sediments (which become rocks), it can't combine with oxygen and thus does not decompose to return that carbon back to the atmosphere as CO2.

So to have a lot of atmospheric oxygen, you have to have a lot of buried organic carbon. Over geological time that carbon tends to turn into coal and oil.

So how can you get around this?

1. Make the planet quite young, in comparison to Earth. Let's say it is in the early phase of Earth's equivalent of the Devonian Period. So there is plenty of life on land, and it will be habitable to humans, but it won't have accumulated the huge coal and oil deposits of our Carboniferous and onwards. The Devonian forests are burying trees like the clappers, but those dead trees are still pretty much all peat or really, really low grade lignite. There will be oil and coal (Earth has Per-Cambrian coal deposits!) but these will be tiny. They may not be commercially viable to extract.
2. The planet did have big coal and/or oil reserves, most of which were right slap bang on the edge of subduction zones. Those rocks have been dragged down into the upper mantle and melted. Downside: when a portion of that molten rock gets erupted back out in any mountain building going on over the top of the subduction zone (like the volcanoes in the Andes), it's going to be instant global warming as it returns all the carbon to the atmosphere.

Answer 3

Fossil fuels come from the non-decomposition of organic matter, if you have sufficient oxygenation in the atmosphere and at depth in the water column then carbonaceous sediments can't accumulate in large volumes. The ocean one is a toss up the current currents in the world ocean prevent any great build up of organic matter on Earth's ocean floors because there's enough Oxygen at depth to break down that material and liberate the Carbon to the food chain and/or atmosphere, that wasn't always the case which is why the Middle-East, North Sea, and Gulf of Mexico oil reserves. Completely unrelated but down here in New Zealand we have oil that's being baked out of relatively young bituminous coal deposits, as in from only 30MYA instead of northern hemisphere coal measures from 350MYA, these coals have a lot of waxy molecules from flowering plants which is why our crude sets at room temperature. Back on point the ocean can either be well mixed or shallow or better yet both to boost oxygen levels and remove the possibility of oil deposits, this assumes and requires a basically passive tectonic history in which ocean topography hasn't changed all that much over geological time, in a tidal lock situation that's not actually an unreasonable assumption. You will still get landlocked deposits of carbon in low-lying areas subject to permanent water that prevents decomposition, in a highly oxygenated environment these will be small, slow to accumulate, of very low grade, and by the nature of the swampy environments in which they're found hard to extract, you're talking about peat and lignite no true coals.

This is a geologically static planet with a very active atmosphere and active nutrient cycles, it's not a total contradiction in terms but thought needs to be put into the cycling of key nutrients, phosphorus particularly, back out of the ocean basins, something like mayflies that take their nutrients from the seabed and return them to land with their mating flight, the way salmon put nutrients into the arboreal forests only dialed up a few magnitudes and all over the world.

Answer 4

Coal and Oil come from millions of years of pressure on biological matter (Plant and Animal respectively). Hence the name Fossil Fuels

• With Oil, it is only efficient when a mass extinction occurs, resulting in many dead bodies in a relatively small area during a relatively small amount of time. If in your world, there is never a great extinction, it is reasonable to say that oil will be in such small pockets that mining for it will not be feasible.
• Coal is a little harder to explain, as plants grow in large groups and leaf litter will result in coal eventually. I see only two solutions here;
  1. In your world, plants do not gather in group, perhaps this is a desert world and large groups of plants are impossible.
  2. Decomposers are much, much more efficient, meaning that dead fallen plants are eaten before they are covered.

Of course unless there is already alien life on your planet, there will be no fossil fuels to begin with because there will be no fossils.

Answer 5

One of the biggest events that lead to oil today is the algae, they converted massive amounts of carbon dioxide to oxygen. They were so effective, they caused an ice age and gone extinct. I guess the evolution thought carbon dioxide to be an endless resource, reminds me of modern humans. The corpses of these organisms became oil. If your world had oxygen to begin with, you might not have such an event. Leading to a world with small amounts of oil. This won't effect coal tough.

Answer 6

In order to explain why there are no fossil fuels you have to explain an absence of mass extinction events. The reason mass extinctions result in oil deposits is the trapping of large quantities of biomass that does not have a chance to decompose and release the carbon back into the atmosphere.

The most likely cause of mass extinction events ( barring consumption as may be the case with humans on Earth, or global war / colonization in the sci-fi realm ) is comet impacts during the early age of the star system, after planets have cooled and complex life has formed. Large sibling planets, a la Jupiter, outside the orbit of the planet in question are known to perturb comet orbits and direct them away from the smaller sibling.

To give some perspective on time spans here, with respect to our solar system:

1. age 4.6 billion years
2. life has been around about 4 billion years
3. the sun will burn for about another 5 billion years or so

It is not clear if this has a very high probability of preventing all impacts on a given planet, but it seems there is a fair chance, with the billions of star systems in a single galaxy, there may be a few where this has happened.

However, this would preclude any of the interesting evolutionary events that also occur after mass extinction events. We do not seem to have a model for that kind of evolution, very long periods, billions of years, of un-eventful ( ha ha ) evolution, and it's not clear what such a model would look like.