The Geography and Ecology of a Supervolcanic Planet

Question

What would be the geographical and ecological implications for an Earth-like planet that experienced intense volcanic and supervolcanic activity on a scale that, while decreasing over time, was far greater during its prehistoric past than anything ever seen on Earth? Eruptions would have had ejecta mass exceeding 10¹⁵ kg and VEIs of 8 or higher. (VEI stands for Volcanic Explosivity Index; 8 is the highest number on this scale that has occurred in recorded history.)

I'm specifically curious about the effect such volcanic activity would have on continents, the fertility of the soil and presence of other natural resources, and, of course, any life that might evolve on the planet in question. Could humanoid life develop on such a planet, or would life be fundamentally different than that of Earth?

Answer 1

Super Volcanism that extreme means that every other magnitude of eruption will be occurring on an enormous scale. Super volcanos are driven by an overabundance of internal heat on enormous plumes of magma emerging from the core-mantle boundary. This also means that plate tectonics, which is driven by convection in the mantle, will be occurring at an accelerated rate. If this world had plenty of water to form continental crust it would be racing (geologically speaking) around building mountains and creating rift valleys.

This magnitude of volcanism would probably create a toxic atmosphere similar to that during the Hadean Eon of Earth which ended ~4000 Mya, but with more sulfur compounds. Any rain would likely be very acidic and the oceans would be acidic too. For the global temperature, I'm not sure because volcanic eruptions release CO₂ and which traps the sun's heat but also ash and sulfur dioxide which has a cooling effect. I will lead towards this world being overall cooler.

Life would likely be some form of extremophile not unlike what you would find near a deep ocean vent. I doubt it would get more complex than some form of algae that can metabolize the toxic atmosphere.

Natural resources would be abundant, every bit of the elemental makeup of the world would make an appearance on the surface and the extreme tectonic activity would expose rich seams of minerals. There would also probably be diamonds everywhere due to the abundance of diatreme eruptions and of course ash everywhere.

Summary: A hellish world with little to no complex life, but abundant natural resources everywhere.

Edit:

After clarification from the OP on his question.

After the Earth accreted and recovered from the moon-forming impact some ~4600 Mya life arose very quickly at about ~4300 Mya but it was not until about ~2300 Mya that oxygen even became present in the atmosphere. There was no real abundant (complex) life on earth until the Cambrian Explosion about ~550 Mya.

So if your planet suffered extreme volcanism, like the Haden Eon, don't expect complex life to arise for about 3500 Million years after the conclusion of the volcanism. That also is about the time it would take for the atmosphere to even support humanoid life.

You could readily end up with a planet very much like Earth 3.5 Billion years after the volcanism.