Question

how do scientists know how hot the core is? *
seismic waves
thermometers
oil wells
by measuring the electromagnetic spectrum

what two elements are the inner core mostly made of? *
carbon and hydrogen
iron and nickel
boron and nitrogen
gold and silver

what is the least dense layer of the earth? *
inner core
outer core
crust
mantle

Explanation:

Seismic waves help study Earth's core temperature. Inner - core is iron - nickel. Crust is least dense layer.

Answer:

1. Seismic waves
2. Iron and Nickel
3. crust