Parts of the Earth may have originally been from another part of the galaxy, having crossed light years to form what we stand upon right now. This is the suggestion of research that says that the Milky Way should be full of flying rocks like Oumuamua, the interstellar asteroid that visited our solar system in October 2017, and they may act as triggers and also as the ingredients to form planets in developing planetary systems.
First came Oumuamua, and then on August 30th this year a comet Borisov was spotted which had come from outside our solar system. From 2023 the Large Synoptic Survey Telescope will watch the sky for such similar objects and it is hoped we will find more than 100 each year. This a wide-field telescope created to photograph the entire sky above it every few nights.
Malena Rice and her team looked at twenty solar systems and found that dark areas where debris must once have been. Until a planet crashed through the objects and sent at least some of them hurtling out of their existing systems. It is highly likely that some of this debris played a part in the evolution of our own Earth.