Whenever he thought about it, he felt terrible. And so, at last, he came to a fateful decision. He decided not to think about it. ~John-Roger and Peter McWilliams
Q:

Dear 100 Hour Board,

When our civilization collapses, how long will it take before its remnants can no longer be seen in the archaeological record?

-Not Wegener

A:

Dear plate person,

This is a lovely question, and the answer is difficult to define, but the science writer Peter Brannen lays it out in "The Anthropocene is a Joke," and essentially, in geologic terms, we would practically not even be visible. Just a blip. We make many changes, but even so--we overestimate our own importance on a geological timeline.

Oh, wait, you said archaeological record. Um, frankly, I don't know. First of all, it depends what you mean. Gavin Lucas, a Cambridge scholar and thinker and author such nerd-books as The Archaeology of Time  and Understanding the Archaeological Record posits the archaeological record is often argued to be one of the three following things:

  1. The archaeological record is material culture
  2. The archaeological record is the material remains of the past
  3. The archaeological record is the sources used by archaeologists

1. Okay, material culture is stuff made by people,"the total body of objects made by, used by, or associated with, humanity." It involves things we made--artifacts--and ecofacts, natural objects associated with human activity--maybe charcoal, collected plant seeds, that kind of thing.

2. Material remains: I don't understand this concept well, but it's like the "remains, traces, residues" left by past human activity. This definition is a little more expansive. Might it include stuff like footprints? I don't know. I only got as far as Intro to Archaeology.

3. Sources: "Everything the science of archaeology has found and created..." "...what archaeologists have learned from the artifacts they have documented. This spans the entire world; archaeology is the human story that belongs to everyone's past and represents everyone's heritage."

I think we're going to go with some vague blend of the first two: I'm going to say anything that seems human, or hominid, is the beginning of our archaeological record, and then choose the oldest one by age.

Now, the oldest known monumental site humans have going on is Göbekli Tepe, in Southeastern Turkey, near the Iraqi border (fun fact! I almost went here once in 2017, but the site was closed to visitors at the time, the nearby museum had to do. We'd putz and fritter around the larger geographic area and eventually rent a diesel car, which a gas station tragically filled with gas, and then the engine went dead in the middle of the Turkish countryside, and we were eventually helped by kind Turkish farmers, but anyways that's another expensive story). Göbekli Tepe dates back some 11,000 years (110 centuries!) to 9130 BCE, which being some 110 centuries and probably at least 160 human lifetimes (optimistically)--is wild and pretty sobering.

But we can get older, much older, because we're not just getting the oldest monumental site, we're going for the oldest archaeological site associated with us, with evidence of hominids--not humans, but a hominid ancestor--might either be the site of Laetoli, in Tanzania, which has footprints in ash going back 3.7 million years, but fossils that are older (how much older? I don't know, friend) or possibly in Ethiopia, (maybe the site of Hadar), with a hominid skull 3.8 million years old.

Okay, that's what I've cobbled together, and now I'm just going to speculate wildly with little-to-no background in any of this:

If there's some record of footsteps from four-ish million years ago, it seems plausible some part of us or something we've made will be around in another four--oh, let's go for five--million years from now. Beyond that, who knows? That first article I referenced in the beginning suggests even a twelve-inch layer of mud left in the geologic record from any of the time humans have existed would be remarkable, indeed:

...Perhaps, perhaps, if one was extremely lucky in surveying this strange layer, across miles of desert-canyon walls, a lone, carbonized, and unrecognizable piece of fishing equipment may sit perplexingly embedded in this dark line in the cliffs. Some “epoch” this...

There's a lot of context to that statement, and I'd recommend just reading the whole article, which is humbling and interesting, and also pretty long. It's a pretty good article, and I have only one criticism of it, for the author has forgotten the one thing immune to the vicissitudes of the archaeological record, the ravages geologic history, indeed, the apparent passage of time:

800px-Queen_Elizabeth_II_in_March_2015.jpg
(source)

Long Live the Queen,

--Ardilla Feroz

posted on 11/05/2020 11:31 a.m.
If you're not limiting us to a *terrestrial* archaeological record, we've left some stuff on the moon that should last a very, very, very long time. If you look at how stuff breaks down, something can come eat it, wind and water can erode it, oxygen can corrode it, and the sun can irradiate it. Without appreciable amounts of wind, water, life or oxygen on the moon, our footprints and garbage should be there almost indefinitely, unless a meteor has some very good aim.
posted on 11/05/2020 3:49 p.m.
An interesting point! But rest assured--the Queen will deal with the Moon and the rest of its meddling spacekind.

--Ardilla Feroz
posted on 11/06/2020 4:14 p.m.
I do not know if the word "archaeological" can refer to items in outer space, but we should also consider that we have sent two space probes (Voyagers 1 and 2) equipped with golden records and a stylus so that intelligent civilization can get a glimpse of our society.

The records contain both pictures and sounds of earth including a description of how we write and use numbers to do math, pictures of the Earth and moon, several instructive images about human biology, and music (including Johnny B Goode by Chuck Berry and works by Beethoven and Stravinsky).

If we count these as archaeological, then those two specs of information will contain recoverable data almost indefinitely, certainly for billions of years.

-The Man with a Mustache

Sources:

https://en.wikipedia.org/wiki/Voyager_Golden_Record

https://space.stackexchange.com/questions/4743/for-how-long-will-the-voyager-records-remain-playable