Scientist have hypothesized the oxygen began to build up in the earths atmosphere after the development of living things with the ability to photosynthesize?
true or false

The image shows ekgs of a person with normal heart waves and of a person having tachycardia. based on this image, what kind of condition is tachycardia? a. the heart beats abnormally fast. b. the heart beats abnormally slow. c. the right atrium of the heart stops working. d. the left ventricle pumps less blood to the aorta.

Which of the following is true of photosynthesis? a)carbon dioxide is a reactant b)water is a product c)most reactions within this process are exothermic d)oxygen is a reactant

What percentage of light hits earth's surface directly?