<span>Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability.
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Decaying tree would be considered a biotic as it is now dead, however it will form an ecosystem of bacteria, fungi and other saprotrophs.
From diffusion of nutrients from underlying layers
Well the U.S. consumes about 7.19 Billion barrels of petroleum related products in 2016.
The U.S. currently uses roughly 25% of all of the world's global reserves.
Hey, America likes oil, leave them alone