Answer to Question 1
A
Answer to Question 2
Seasonal variations occur because Earth's orientation to the Sun continually changes as it travels along its orbit. Earth's axis is not perpendicular to the plane of its orbit around the Sun. Instead, it is tilted 2312 from the perpendicular; this is termed the inclination of the axis. If the axis were not inclined, Earth would lack seasons. The seasonal variation in the angle of the Sun above the horizon affects the amount of energy received at Earth's surface in two ways. First, when the Sun is directly overhead (at a 90-degree angle), the solar rays are most concentrated and thus most intense. The lower the angle, the more spread out and less intense the solar radiation that reaches the surface. Second, but of lesser importance, the angle of the Sun determines the path solar rays take as they pass through the atmosphere. When the Sun is directly overhead, the rays strike the atmosphere at a 90-degree angle and travel the shortest possible route to the surface. This distance is referred to as 1 atmosphere. However, rays entering at a 30-degree angle must travel twice this distance before reaching the surface, while rays at a 5-degree angle travel through a distance roughly equal to the thickness of 11 atmospheres. The longer the path, the greater the chance that sunlight will be dispersed by the atmosphere, which reduces the intensity at the surface.
The site of Dmanisi has produced some of the earliest H. erectus outside of Africa.
A sod house in North Dakota, 1896. Individual “bricks” of sod were hewn from the ground and stacked
This internal bypass passage in the thermostat housing directs cold coolant to the water pump.
Growth in Cold and Cool Clouds
Action of type I and type II topoisomerases, as shown by gel electrophoresis
Countries where malaria is prevalent today are located in the warm tropics and subtropics