How Long Would It Take For A Car To Erode Near-Seamlessly Into The Environment?

Question

I'm writing a short story that takes place many decades into the future. A major plot point is that a car that was promised to a future archaeologist via inheritance has naturaly eroded to the point that only a few scraps remain.

The following are true.

• The car was parked in a remote field in rural Oklahoma.
• The car is not near a body of running water, is not in direct sunlight, and is parked on rocky soil that cannot support large amounts of vegetation.
• No human being had ever interacted with the vehicle since it was abandoned. Either directly or indirectly.
• The car is parked in the partial shade of a rock crag.
• All that remains of the car are a few scatted pieces of scrap to signify that a car was once parked there.
• The car in question was a slightly used 2019 Honda Civic.

Only taking natural forces into account, how long would it take the car to near-seamlessly erode into the environment while still leaving some material trace?

Answer 1

I feel very comfortable with a prediction that a Honda Civic left unattended and exposed to the elements would be recognizable as having once been some kind of car 100 years ago but now little more than rusty bits. I expect there to be little to even suggest it was a car after 200 years apart from the engine block and drive train.

We have an abandoned car that looks to be 70 years old in our forest (admittedly not a field). It is almost completely disintegrated. I only know it is a car because I took a good look at the odd rusty thing sticking out of the ground.

Here is an image of cars from the (in)famous Belgian Car Graveyard.

These were working cars at the time they were abandoned. A mechanic did not know what to do with them in 1966 following France's withdraw from NATO.

Even in dry places cars disintegrate rapidly. These cars were abandoned about the same time (60-70 years ago):

Finally, here is an actual 1978 Civic happily on the entropy highway. It is 42 years young and stored in a barn out of the elements!

Answer 2

10 years - car looks the same, tyres are deflated.

100 years - car's paint failed, car looks rusty all around. Interior rot away, with dust and goo covering the insides.

1000 years - through holes became much more noticeable, doors fell off, front window fell in. Soft insides are empty, dried and wiped away by the wind, just bare metal and solid plastic remains visible.

10 000 years - structure completely collapsed. Car's middle part is now thin, trunk is a bit higher, motor is the most noticeable part - as a pile it is higher. You can recognize that it is a car only from front glass - it is now dark from oxidized plastic layer inside, but shape is recognizeable.

100 000 years - majority of the mass in this pile is not from a car anymore. Even slightest wind would have by now removed rusty particles and oxidized plastic particles, and add natural dust instead. Glass still can be seen partially exposed from the pile, sanded down to a matt surface by even a slightest wind.

1 000 000 years - at this time scale diffusion begins to play a role. Even remaining glass parts will begin to diffuse with particles around them, merging on the surface. Pile will become one solid rock.

Answer 3

Regardless of how fast it actually disintegrates, in a few hundred years at most it will be covered by dirt and other debris, therefore cannot be found without digging. Objects tend to "settle" into the earth. This is caused mostly by wind pushing sediment against the object, along with seeds that produce vegetation that attract even more debris. In a hundred years, you probably can see some of it. In two hundred, maybe not. Maybe an object on a high rocky mountain would be visible longer, but that venue seems largely inaccessible for your story type, and is pretty far from what you envision already.

Answer 4

There's one thing to keep in mind about parking this thing in Oklahoma: the wind is infamous for a-sweepin' down the plain. The trivial answer to your question is "until a tornado hits it". If you don't get hit by a tornado but are simply in the general area near one, you can experience wind gusts of 100-150 mph over a swath nearly a half mile wide. Being hit by flying debris at those speeds - or by the large hailstones that frequently accompany tornadoes - can tear a car to shreds (it's like being hit by a baseball that was dropped from an airplane at cruising altitude). Even Oklahoma's non-tornadic winds can throw gravel and small rocks hard enough to put a deep gouge in the paint, crack glass, and bring tree limbs down on top of the car.

Once the car's outer protection is damaged, the real deterioration begins. Exposed metals start rusting out. Plastic parts will photodegrade over time, and rubber parts can dry out, stiffen, and crumble within a decade. Critters move in and start tearing up the interior. Once it sits long enough, the ethanol can separate from the rest of the gasoline and start corroding the vehicle from the inside within a few years. Once the tires go flat and disintegrate, you'll have metal parts in contact with the ground where they'll encounter more moisture and rust faster.

As all these components start breaking down and falling apart, the Oklahoma wind will blow the loose bits away. The prairies of Oklahoma naturally experience wildfires every 1-30 years, which will strip your car of anything left that's remotely flammable.

The final remaining pieces of the car that will be left over and in a recognizable state will be portions of the engine block. It's a large, solid hunk of metal and will take a very long time to rust away completely. It's possible that some of the large fiberglass body panels might be recognizable for a while, but only if they can manage to stay in pieces large enough to not get blown away. Some large portions of the metal frame may also still exist, as they're typically treated to inhibit rust.