Remnants

During millennia of space exploration, human travellers found remnants and ruins of ancient alien civilizations. It was "Knock, knock, who's there?" but there was no answer...

Had any stranger passed by he would have wept also; for the whole flower garden was wrecked; naught remained but trampled mould and remnants of plants, with here and there some solitary flower that had escaped being crushed to pieces, and which with its colours yet gay and bright looked still beautiful, though fallen.

Pulsars are dense remnants of dead stars that regularly emit beams of radio waves, which is why some call them "cosmic lighthouses."

Soon the disenfranchised, downtrodden laymen started a full out uprising, seeking to tear out the remnants of their oppression.

Microplastics — the remnants of plastic bags, takeout containers and straws that almost-but-not-quite disintegrate in the oceans — are found in 3 out of 4 fish, such as squid, cuttlefish and swordfish in markets around the world.

In a study published Wednesday in the science journal Nature, Laurentian University geologist Elizabeth Turner detailed how she found fossilized three-dimensional structures that resemble modern sponge skeletons in thin sections of rocks taken from the remnants of a prehistoric ocean reef.

The Western Wall is one of the few remnants of the Temple in Jerusalem.

A really interesting research paper is "KIC 8462852: Remnants of a Failed Early Type II Civilization?"

King Ziri continued to chase the remnants of Rima's army across the country.

Archeology is the science that studies the remnants of human civilization.