A seismologist plots the variation in velocity of Pand Swaves in different layers of the Earth during an earthquake. The information is shown in the graph. 15
P waves
10
Speed (km/s)
Swaves
Crust
Mantle
Outer core
Inner
core
0
1,000
2.000
3,000
4,000
5,000
6,000
Depth (km)
What can be concluded from the graph?
The layers of Earth have different densities.
O P and S waves are absorbed in the core.
The layers of Earth do not have distinct boundaries.
O P and Swaves always originate in the mantle and travel through the core.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

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chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.