Which of the following describes a positive feedback loop?
when blood sugar is low, the body sends hormones that increase blood sugar.
when the body senses that the heart rate is very high, it secretes hormones that decrease the heart rate.
when a pregnant woman begins to go into labor, the body sends hormones that increase the intensity of the labor contractions.
when someone is exercising intensely, the body sends hormones that increase oxygen supply for cellular respiration.

1. the geologists have established a set of principals that can can be used o determine the relative ages of rock. this principal is applied to sedimentary and volcanic rocks. the rocks exposed to wall of grand canyon has layers and by studying the number of horizontal layers in the rock(strata) the relative age can be determined. the layer first formed will appear at the bottom and the the layer of strata last formed appear at the top. by using this information the approximate age of rocks can be determined.

2. carbon dating is used to find the relative age of rock in numbers which means for the rocks that has age between 1-70,000 years.

3. for the rocks of age range between 1,000 - billion of years potassium-argon dating is used.