Oceanic crust is more dense which makes it subduct and continental crust is less dense which makes it override the oceanic crust during subduction
for better research go to under NOAA - Climate.gov
This is a short paraphrased summary of the article about ice cores in that website.
Answer: Researchers in labs may melt or crush bits of the ice core a little at a time, each deeper layer shows the time in the Earth's climate history. Tiny pieces of pollution, metals, radoiactive fallout, pebbles, sea salt, volcanic ash and even air bubbles all present important information that researchers can look for to track changes in the atmosphere's composition and temperature.
They have a Dictatorship, because their Government controls all factories, businesses, what you do, and where you go.
I’m pretty sure it’s the Inuit people hopefully I answered it correctly