Why does excessive exercise cause muscles to become stiff and sore?
During vigorous exercise, the circulatory system cannot supply oxygen to uncle fibers quickly enough. In the absence of oxygen, the muscle cells begin to produce lactic acid, which accumulates in the muscle. It is this build-up of lactic aid that causes soreness and stiffness.
What causes sinkholes?
Sinkholes are usually formed by the dissolving action of groundwater or the seepage of above-ground streams into the limestone below, causing cracks or fractures in subterranean rock.
Which chemical element is the most abundant in the universe?
Hydrogen (element 1) makes up about 75% of the mass of the universe.