"Ancient mystical texts hint at earlier creation, the life that preceded the Garden, prequels to Genesis. These incarnations are not reported in the Bible because they are none of your goddamn business, but the evidence is everywhere. Some students of conspiracy believe there was a time when lizard people shared the earth with modern men, the older race dying as the younger emerged from the forest. The last of the lizards were worshipped as gods; these were the deities of ancient India and Greece. The technology—weapons and machines—created miracles. You can see the lizard kings in carvings from Mesopotamia, the oldest historical records, where humans bow before reptile men. You find them again in the Torah, where they appear as Nephilim..."

So current human population is 400 thousand times the maximum T-rex population at any one time. A few decades are enough to produce more human individuals than the entire T-rexes history. We also have the ability to go (and die) pretty much anywhere, so there will be human skeletons in every crevice, depth and environment on Earth. We also produce an absolutely staggering amount of artifacts of all kinds, from plastic straws to giant tunnels and artificial caves. There are zero chances an advanced civilisation on Earth won't be aware of us in 400 million years.

I think this is it: the point of this argument is to inspire some awe in the listener, making them realise how vast Earth's time is compared to our horizons.

But in practice, the argument is wrong. A dead animal's skin is expected to lasts weeks to months- and yet we have fossilised specimens. A footprint typically lasts hours, and yet we have ones that are hundreds of millions of years old. Even if the expected lifespan of our artifacts is nothing in comparison with these timespans, a small percentage of artifacts will either be preserved or leave recognisable traces- exactly as it happened for soft tissues and footprints. It's extremely naive to think that none of this will leave traces.

That is completely incorrect. We have sedimentary rocks from 100 M years ago on the Earth’s surface right now, that never underwent any kind of subduction.

Subduction only occurs at plate boundaries and is not nearly this fast. Continental plates float on top like foam and do not get subducted. It's the oceanic plate that is created at mid-ocean ridges and gets subducted at the margins.

2.) Other civilizations even in the nearest solar system would basically be impossible to detect. Even in our own solar system, there could be millions of undetected spacecraft right now. They're simply too small to see. To be detectable, they'd either have to be massive and massively disruptive, like Dyson spheres, which are and most likely will forever remain pure fiction, or they'd have to happen to use radio for communication.

3.) There are good reasons for them not to be using radio for communication. They might have discovered a different physical phenomenon that allows them to communicate in ways we can't detect. Or they might not be as reckless as humans and don't want to broadcast their presence and activity to completely unknown and potentially hostile other species.

At that age we can be pretty sure they did not have industry but they could have been like tribal hunter gatherers. If they did not build a lot and at large scale we’d have basically zero chance of finding anything. Stone, wood, animal skins, pottery, arrow heads, tools, etc., all that would be long gone. Metal would too but it might leave diagnostic traces, as would synthetic chemistry (plastics) or large scale fuel use.

Birds, the modern still living closest relatives of dinosaurs, are often strikingly intelligent especially relative to their brain mass. Dinosaurs had small brains relative to body size but while there is a correlation there with intelligence it’s not perfect. There’s exceptions, animals with small relative brain sizes that seem very smart, like elephants.