Answer to Question 1
D
Answer to Question 2
The nature of the layers, their properties, and the forces that influence them have been learned largely by the study of shock waves associated with distant earthquakes. Seismic waves, low-frequency pulses of energy generated by earthquakes, can spread rapidly into Earth in all directions and then return to the surface. Sensitive seismographs have allowed researchers to study the ways seismic waves refract and bounce off abrupt transitions between Earth's inner layers.
If Earth were uniform (homogenous) throughout, seismic waves would radiate from the site of an earthquake in straight lines. If the density, or rigidity, of Earth increased smoothly with depth, seismic wave velocity would increase evenly with depth, and the waves would gradually bend upward toward the surface. If Earth were layered inside, some seismic waves would be reflected at the boundaries between layers, whereas others would bend. Seismic evidence shows that Earth is layered.
The span of Homo sapiens sapiens’ time on earth
the fatty acid molecules expose the smallest possible hydrophobic surface area
Relationship of the electrocardiogram to electrical conduction in the heart.
Conduction system of the heart.
Earth-Moon-Sun Positions during the Spring Tide
Cardiac conduction system