Why does gravity cause layers of sediment to be horizontal

The truth about this is that all across the earth's surface there is gravity. So what happens is that sediments will deposit parrele on Earth's surface which is horizontal. Basicaly explained, As more sediment is added, it is compressed and then it is hardened into rock layers. 

Iam pretty sure it is c. 2000 bce

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].