What are the two sources of thermal energy in Earth's interior? A. solar heating and gravity
B. combustion and solar healing
C. radioactive decay and combustion
D. gravity and radioactive decay

What overall charge must all compounds have

Significant figures are digits read directly from the measuring instrument plus one more digit, which is __ by the observer.

Which set of characteristics best describes igneous rock? a) largest type of rock, made of organic matter, hardest type of rock b) least abundant type of rock, made of other rocks, made mostly of minerals c) found on all continents, contains wavy bands of stripes, contains fossils d) most abundant type in earth's crust, made of magma/lava, contains no fossils