6. eons are the broadest category of geologic time, and we live in the phanerozoic eon. the
phanerozoic eon is further divided into eras. what divides the three eras of the phanerozoic
eon?
rams
o a. mass extinction events separate the three eras from each other.
o b. the first life on earth and the first multicellular life on earth separate the three eras from each
other.
o c. the appearance of carbon on earth and the appearance of atmospheric oxygen separate the
three eras from each other.
o d. the development of insects and the development of flying insects separate the three eras
from each other.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds