Sedimentary rock indicates the current or past existence of ___.
water
lava
plants and animals
carbon dioxide
------


Choose ALL the answers that apply.

The crust is:
the thinnest layer
made of large pieces called plates
mostly made of silicon dioxide
the outermost layer of the earth
also called the hydrosphere
---


The ozone layer _____.
is part of the troposphere
is used to send radio signals
protects the earth from UV radiation
is made of charged ions and free electrons
---