Is there any way that someone now can deliberately add a verifiable date to an object/structure/etc.? Something that a million plus years from now would objectively demonstrate the age to a researcher of the future.

Considering the strong tendency to disregard old written historical records people of the future will likely face a similar dilemma attempting to accurately date any ruins of our present day buildings.

Maybe you could engrave the relative positions of some nearby stars onto a plaque or something like that? Ceramic lasts basically forever, right? Maybe you wouldn’t get “Tuesday, Deceduary 110th 2132” level of precision but you could perhaps get something pretty precise with the right choice of stars?

We know what the positions of those stars were back into the ancient past and forwards into the distant future. We can engrave positions corresponding to any date we like onto such an object. It provides no proof of date.

There's no need. All of our biological waste (e.g. wood) will provide reliable carbon dates within the range of ~50k years. Radioisotope ratios in our metals and construction materials can be used to date our inorganic ruins on geologic time scales.

Radioisotope dating doesn't work for stone structures like the one described in this article, because it would date the age of the stone, not the structure. But concrete is poured, and steel forged or reforged at or close to its actual use date. So radioisotope ratios in these materials ought to give a reliable dating mechanism on very long timescales.

Someone could put hermitically sealed cartridges of something that will decay nicely into a high visibility container that's designed to stay permanently built into the structure itself. Future humans could drill through the solid exterior and retrieve samples of the decaying inner material providing definitive means of precisely dating the structure. Designing it to be used more than once by successive generations would help keep future history more accurate than ancient history.

Why bother? Radiocarbon dating is only good up to about 50k years. Longer than that and you would use longer lived radioisotopes which are in the construction materials anyway.

The article specifically says that they "drilled down into the hill and collected core samples that allowed them to use radiocarbon dating techniques to learn the ages of the layers that make up the hill."

They didn't randomly pickup dirt from the base of the pyramid and date it as you seem to be implying, they used the standard method of taking core samples at various depths to find the dates of the various layers of the pyramid. Based on that they made the claim.

The radiocarbon date of the material used in the construction of the hill doesn’t change when it is pushed around to make a hill. That dirt was already old.

I would advise reading the study as it provides much more information, including stratigraphic profiles of 4 different layers, maps/images of the trenches, borehole data, and various remote sensing surveys.

Unit 1 (surface): 2,000-1000BC Unit 2 : 6,000-5000 BC Unit 3: 24,000-14,000BC Unit 4: NO data

Unit 2 is clearly artificial and represents a construction layer. It has pieces of cut columnar basalt aligned parallel to the ground -- which does not occur naturally, so it is undisputedly artificial.

The soil filled on top of Unit 2 contains homogenous radiocarbon dates and no weathering indicating it was placed all at the same time.

They unit 3 layer contains weathered rounded boulders stacked on top of each other -- this type of weathering normally occurs in a stream an their presence on top of a hill does seem to indicate they were placed there. They also seem to be placed into structures forming a wall. While it is less obviously artificial than unit 2 -- they still provide some compelling evidence that it is indeed artificial.

They claim unit 4 is a natural andesite lava flow that has been "sculpted", but I don't see any evidence to back up that particular claim in the paper, unless i missed it.

TLDR: they did exactly what you mentioned -- took samples from above / below / inside various construction layers, and the dates match the stratigraphic context.... It wasn't just 'scooped up in the vicinity of the pyramid.

I agree given the nature of their claims, it would be ideal if they included another dating method like OSL to go along with the radiocarbon dates, but the radiocarbon dates themselves are not as half-hazard as you make them out to be.

https://onlinelibrary.wiley.com/doi/10.1002/arp.1912

That's not what I mean by "in context." For radiocarbon dating, the term "in context" means that it is established that the radioisotopes were captured at a time coinciding with or in some way limiting upon the date of the activity under consideration, in this case the construction of the pyramid structure.

1. Soil is alive--it is constantly interacting with the atmosphere, if it is close enough to the surface, and the nutrients which seep through it and the various organic matter that lives inside it. You might be able to reliably date a peet bog or other undisturbed anoxic system, but packed soil in a tropical environment is a bit more suspect (no matter how buried). Otherwise the "date" of the soil is continuously evolving based on local conditions that are difficult to calibrate. That's why archeologists typically date things like the charred remains of a cooking fire, not soil.

2. Ok, assume that these dates are in any way meaningful. That still doesn't establish the age of the structure as claimed in the article. Surface dates are totally suspect for the reasons I gave above, but for the purpose of this point we can grant it. So Unit 1 provides only an unsurprising minimum age. The packed dirt in Unit 2 & 3 on the other hand is construction back-fill: the radiocarbon age of the packed soil is the average age of the soil they used in construction. But that soil was already old. Think about it this way: if you took that surface soil from Unit 1 and put it on top of your house porch, we'd now be able say your porch was constructed between 2,000-1000BC.

This article establishes that there were two construction phases, and that these phases were likely carried out at different times because different sources of back-fill soil were used. But that's it. The actual dates have no relation to the human activity.