If the Earth was destroyed by a cataclysmic event such as a large mass colliding with it, such that it fractured into multiple pieces, would any trace of human civilisation remain intact ?
I.e., if some alien race discovered the remnants and thoroughly examined them, would they find anything that would suggest that a civilisation once existed on that world?
If so, would these traces include substantial things like buildings or structures remaining intact on pieces of the fractured earth?
Even if Earth's surface will be completely cleaned, there is a chance that alien scientists would notice some signs of civilization left on the Moon or a near planet.
If the catastrophe was not big enogh to disrupt Earth gravitation field it is also possible that some of more than 3000 satellites will be still orbiting the planet.
An impact like that would not "fracture" the Earth, it would "splat" it, like if you shot a big drop of water with a BB gun. On large scales like that, there is nothing that is "solid"; everything behaves like fluid or putty. You cannot even drill 10 kilometer down into the "solid" crust of the Earth without the bedrock closing in on the hole as if it was a malleable material being squeezed.
With an event like that, every place on Earth will have an earthquake that is entirely off the scales. The crust of the Earth will ripple and flex in completely unimaginable ways. This will shatter any and all man-made structures.
And even if you would get some really large chunks, these will eventually crumble under their own gravity and form new spheroids. Nothing will remain standing because the very ground we stand everything on will have shaken so violently that no structure will remain intact.
That said...
Even a pile of rubble is a trace. If your aliens' scientists are worth their salt, they will notice very curious distributions of materials. There will be billions of blotches and spots all over the place where they find concentrations of compounds that just cannot form on their own.
The one thing that can stop this is if the partitioning is so violent that the extremely thin crust that we live on gets crushed, blended and mixed into the hot contents of the rest of the planet as the chunks collapse under their own gravity. Unfortunately — for you — it is not at all unlikely that this is exactly what will happen.
This however is not unlikely is that what you meant to say?
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Mar 7, 2017 at 14:06
Any impact large enough to 'fracture' the Earth, would first melt it. For example, the impact that made the moon likely liquefied the entire crust. In that case, there will be nothing identifiable on the Earth. Other answers mention this that and the other thing that might be recognizable; but liquefaction and a vigorous stirring (since there is no other way to describe being hit with a moon sized object at 4 km/s) would mix all evidence of humanity in with quintillions of tons of water and rock and mantle until nothing could be identified, with one exception mentioned below.
Another comment points out that the liquefaction of Earth would likely not leave much standing on the near side of the moon. However, there are a few probes lost in the vast-ness of deep space, and some broken-down rovers on Mars that will be there for some time. Not that long, in the case of Mars, due to the dust storms.
While you could not identify a layer of activity to associate with an 'Anthropocene', given the vigorous mixing mentioned above, alien geologists would know something was up. We humans have made non-trivial amounts of some elements that should not be there. The fission yield curve shows what nuclear wastes are produced in what relative abundances. Of the seven long lived fission products in nuclear waste, Technetium-99, Cesium-135, and Zirconium-93 are each relatively common.
Alien geologists, assuming they showed up in the next 1-5 million years, would wonder where all these unexpected isotopes on an otherwise barren world came from. Or maybe they won't wonder because they are Daleks and they sent the planet-liquidizer.
It strongly depends on which level of details they can examine the sample.
There are many traces that indirectly point to a civilazation.
So these traces would suggest that a civilization existed. Large structures would remain, again, not as big thing (no Coliseum or Big Ben for them to look at), but as a distinct chemical trace ( a skyscraper would maybe leave a lump of molten steel derived from its supporting frame, together with methamorphic rocks originated from the concrete and building stones)
Sufficiently advanced civilizations leave a geological record. Let me quote from Anthropocene (Wikipedia):
The Anthropocene has no agreed start-date, but one proposal, based on atmospheric evidence, is to fix the start with the Industrial Revolution (late eighteenth century)
[...]
Fossil record
Increases in erosion due to farming and other operations will be reflected by changes in sediment composition and increases in deposition rates elsewhere.
[...]
Trace elements
In terms of trace elements, there are distinct signatures left by modern societies. For example, in the Upper Fremont Glacier in Wyoming, there is a layer of chlorine present in ice cores from 1960s atomic weapon testing programs, as well as a layer of mercury associated with coal plants in the 1980s. From 1945 to 1951, nuclear fallout is found locally around atomic device test sites, whereas from 1952 to 1980, tests of thermonuclear devices have left a clear, global signal of excess 14C, 239Pu, and other artificial radionuclides.
If it would be possible to examine the composition of the fragments, geologists could extrapolate geological events related to technological eras. This would be similar to today's geologists knowing the composition of the atmosphere millions of years ago just using the fossil record.
Please note that traces of the anthropocene exist all over the world, not only in inhabited areas.
The question would be whether the cataclysmic event would completely obliterate the geological record (imagine nuking an archaeological site), or add on top of it (imagine dropping napalm on an archaeological site, with enough napalm residue to make an extra layer on top).
A planet being ripped into an asteroid belt due to high gravitational tidal forces is very much like the formation of a planetary ring. Imagine you could send some geologists up to Saturn, and bring back some chunks of its ring. Would there be big enough fragments of the crust to see the geological eras? Or would the fragmentation melt everything together? The harder the cataclysmic event, the harder the geology/archaeology gets.
On the surface, probably not.
While a comment noted that an impact large enough to "fragment" a planet will behave more like a "splat", the implications of this have largely been missed. Such an impact will produce an enormous cloud of ejecta (a significant fraction of the planetary mass) which will mostly fall back to the surface. This will have two effects.
First, the impacts will produce an enormous amount of heat, and a lot of the impact areas will become molten, erasing any signs of man-made artifacts.
Second, even a small fraction of the planet's mass will bury the remnant surface very deep. For instance, assuming uniform density, 1% of the earth's mass will produce a blanket about 13 miles deep. Given the scale of the ejection event, a fairly uniform coverage should be assumed.
As a result, any visiting aliens had better be interested in relatively deep (much deeper than we can do) exploration of the pathetic remnant of a once-living planet. Exposure of core material at high temperature will have locked up all the atmospheric oxygen, and for quite some time the surface temperatures will be high enough to keep the water as vapor (that is, steam).
Of course, you may have noticed a possible loophole in the opening sentence of this answer. The ejecta will not entirely return to the surface, and for a shorter or longer period some of it will orbit the earth - we'd probably have a very nice set of rings for a few millenia - and if the visitors are lucky they might encounter artifacts in orbit. The odds on this are not great, but I don't see how they would be zero, either. You'd expect to see fragments of refined metal, and small, dense objects might survive the ejection process in a recognizable form. This might apply to objects such as steel tools and jewelry. Platinum, for instance, is quite hard, strong, and melts at very high temperatures.
EDIT Even a badly damaged Rolex would be a pretty sure sign that someone had been on the planet.
Unless, of course, the Blind Watchmaker debate is universal. END EDIT
If the Earth is destroyed to the point of melting the crust and destroying all possible artifacts, there are still those that were not on the Earth at the time.
Besides artifacts on the Moon, Mars, Venus, Titan, and various radioactive radio-sending beacons heading slowing to the Oort cloud, there is a cloud of sattelites including many in a rather distant Geosynchronous orbit. These may be scattered rather than vaporized. Even if the expanding cloud batters them, they will also move away and at least some of them may remain as recognisable anomolies in the debris.
Assuming current level technology, the first thing the aliens will find on their scanners would be radiation spots from the melted down 447 nuclear reactors that are currently active.
This would be a pretty unmistakable sign of civilisation.
There are actually some fairly significant artifacts which would be much easier to discover than anything on the Moon, Mars or things like puny inter planetary probes...
There are five S-IVB Saturn V third stages in heliocentric orbits, and they are all obviously artificial to anyone looking for them. Being that they are twice the size of a London bus, they would be the most likely artifact to be found by anyone surveying the solar system.
Such a collision would eject significant mass from surface. Nearly all of that mass would fall on the surfaces of Earth and Moon. This would melt and reform both surfaces removing all traces of us on either surface. It would also destroy all satellites orbiting Earth or Moon. This is supposed to be how the Moon was created. (Probably without the part about the traces of advanced civilization being erased?)
The collision would do nothing about traces outside the Earth-Moon system, so given some time a record of our existence could be launched to stable orbit in space. Earths L4 and L5 points, maybe? So if you want the aliens to find traces of us, it is easy to do. Kind of interesting to think of what we would choose to record of ourselves and what the aliens would think of it, really.
...if some alien race discovered the remnants and thoroughly examined them
As the OP implies, let's assume no limits on the practical abilities of our aliens to filter the debris (i.e. they are arbitrarily good at forensic study).
Diamond (melting point ~4500K) should survive immersion in magma at the temperature of the mantle (~4000K). Therefore, they will find unnaturally cloven gem-stones. The golden ring will melt, the hand that wore it will vaporize, but the gem will remain. Love, truly is eternal.
The proportion of the different - stable - isotopes tend to be the same in the whole Universe.
Nuclear reactions change these proportions, and thus they remain visible forever even after all of them decayed, even after trillions of years.
Although our radioactivity changes only a very small part, compared to the mass of the whole Earth. If somebody would mix the whole volume of the Earth, we couldn't measure anything in it.
It depends the technology earth had at that point. But radio-waves would remain, sadly most of the first human things they may have heard, would be Hitler. Still our legacy may remain and maybe would be possible to pinpoint earth's position. Plus our many satellites and debris would scatter.We would always have the probe we are sending to the edge of solar system (forgot the name) it contains several artifacts from earth including a map to find earth,blood and also music!
