When I did a lot of work in them, there were two basic models, one conventional, one quite radical, that were fought over in publications, at meetings, and in the field. I had the privilege of spending time with adherents of both schools.

More to follow…

The theory I heard was that the Glaciers of ‘snowball Earth’ essentially erased 500 million years of geologic history…

There was a science fiction book that had- as a minor plot point – the revelation that a sentient technological species existed on earth during this missing period…

It was ‘The Light of Other Days’ by Arthur C. Clarke and Stephen Baxter…

Perhaps I do not have a deep enough appreciation of how deep ‘deep time’ is- but I think that a global civilization like ours would still leave easily discernible traces even after a half billion years… Just look at the extensive mines we make, the precisely patterned geological alteration of huge swaths of land we make with our cities- those will be obvious for 100′s of millions of years. The glasses and ceramics we make that are of obviously intelligent design will be far more likely to be preserved than bones.

We have even found the remains of a 2billion year old (natural) nuclear reactor and dissected it enough to reconstruct an idea of how it worked… (Don’t tell Johannes)

One of the reactors released 15,000 MWth.years of energy and consumed six metric tonnes of uranium. It operated over several hundred thousand years at a low average power of 100 kWth. Sixteen reacting zones where these natural reactors occurred have been identified.

The strata laid at the bottom of the ocean during the anthropocene will bear chemical evidence of a technological civilization…

I think that we can safely assume we are the first technological species on Earth, since had there been another, we would know it already.

I’ve got to catch a plane in a few hours so I’ll give your question its due consideration at 30,000 feet and get back to you.

The biggest question that nags me is the formation of greenstone metamorphic belts.

(https://en.wikipedia.org/wiki/Greenstone_belt)

The arising of complex life forms (the Cambrian Explosion) may not have been a particularly rare event in earth’s history, maybe that was just the last time it happened, since we haven’t had another snowball earth since. And since no fossil evidence of any previous metazoan ages survives, could it be there weren’t any?

Or, then again, maybe pre-Cambrian metazoan fossils have all been subducted into the mantle, the evidence destroyed. Maybe they have evolved multiple times in earth’s history and we have no way of knowing it!

Either way, I guess there still may be a few surprises left to be uncovered and explained in geology. Any guesses or speculations? Tell me, as a geologist yourself, what big puzzles remain to be resolved in your discipline?

Astronomy has Dark Matter and Energy, and galactic evolution has never been fully worked out. We still don’t know if life or intelligence is present in the cosmos (other than earth). Biology had its last big breakthrough in 1959, with DNA. Physics had its last big paradigm changes with Relativity and Quantum Theory, about a century ago. The latter led to the last big revolution in Chemistry, the nature of the chemical bond.

Is there anything in geology comparable to say, plate tectonics or the dinosaur-killer asteroid, that is still not fully understood, or waiting to be proven or discovered? Remember, both were 20th century discoveries. What kind of major revolutions can we expect in geology in the next century or so? What major problems can we expect to solve?

https://www.livescience.com/64692-snowball-earth.html

Although radiation can increase the mutation rate, its effects can also be negative for life, and multicellular life is less resistant to radiation than single-cells.

I’d forgotten about “snowball earth”. When did that occur, and how long did it last? Did it also affect the tropical oceans?

But enhanced radiation causing DNA mutations is a very compelling idea.