On remarkable realization associated with the discovery of sea floor spreading was that

Compared to continents, the crustal floor of the oceans is very young.

Explanation:

This is true because oceanic crust is constantly being recycled. It is subducted into the mantle where it is destroyed and new oceanic crust is produced at mid-oceanic ridges, so it is younger than the continents.

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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.