How do we know what the earth was like
before humans existed?
Tree rings, ice sheets,
and sediments on the ocean floor
reveal how our planet’s temperature
and ice cover
have changed over the course of
hundreds of thousands of years.
For example,
scientists can determine prehistoric temperatures
by drilling deep into the ice
in places like Greenland and Antarctica
and analyzing the makeup
of ancient snow.
Similarly,
scientists have figured out that the
shells of marine microorganisms
carry indicators of how salty the ocean is.
By looking at shells that have decomposed and settled on the ocean floor,
they can estimate the volume of ice on the planet
thousands of years ago.