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 Sun's Surface
Earth’s history is divided into nested sets of time--eons, eras, periods, and epochs--and is called
Earth’s history spans 4.5 billion years. Geologists and paleontologists have pieced together the his
Scales of Atmospheric Motion
Earth-Moon-Sun Positions during the Neap Tide
Daily Variations in Temperature and Relative Humidity