My Personal Summary
This textbook offers an introduction to physical geography, which is the study of the interactions between the Earth’s climate system, landscapes, oceans, plants, animals and people.
Part 1: Atmosphere, Oceans, Weather and Climate
- The layer of gases surrounding the Earth rises about 500 kilometers above the surface. The troposphere is the lower level of the atmosphere that extends about 6 kilometers above the surface and is responsible for the weather we experience.
- The release of energy from the Sun is the main driver for water, air and wind motions and most life on Earth.
- The Earth absorbs a small percentage of radiation from the sun in the form of short-wave radiation and reflects it back towards the atmosphere in the form of long-form radiation.
- About 78% of Earth’s atmosphere is nitrogen, 21% is oxygen, and only 1% is a mix of methane, nitrous oxide, carbon dioxide and other gases. However, these are the gases that absorb the thermal energy emitted by the Earth and radiate this energy back towards Earth, providing a heating effect.
- The same thing happens in a greenhouse, in which glass allows short-wave radiation to pass through it but then traps the long-wave radiation reflected by plants, creating warmer air inside the greenhouse. This is where the term greenhouse effect comes from. This effect is actually a good thing because it keeps the temperature of Earth warm enough where humans and other organisms can thrive.
- There are two main processes that drive global wind circulation. (1) The uneven distribution of the Sun’s radiation over the Earth’s surface. Since the Earth is a sphere, solar radiation is spread over a larger area near the poles compared to the equatorial regions where it is more concentrated. Since heat is always transferred from hot materials to cooler materials, the warm air from the equator will naturally try to rise and move towards the poles. (2) The second driver of global wind circulation is the Earth’s rotation. Winds move right in the northern hemisphere and left in the southern hemisphere, known as the Coriolis effect.
- The Earth is tilted at a 23 degree angle, which causes the four seasons. When the Earth’s axis points towards the sun, it it summer for that hemisphere. And when it points away from the sun, it is winter for that hemisphere.
- Trade winds are winds that blow from east to west around the equator at lower levels of the troposphere. These are winds that sailors used to take advantage of when sailing from a western location (like Europe) to an eastern location (like North or South America).
- There tends to be a greater amount of the Sun’s energy received in the form of ultraviolet energy in mountainous areas.
- At around 30° north and south there are major zones of descending air which are clear and dry and this is where most of the world’s large deserts are found.
Part 2: Climate Change and Carbon
- The Earth has been around for about 4.6 billion years. Ice sheets have existed on Earth during the past 2.4 million years. This period is known as the Quaternary period. The start of this period was initiated by plate tectonics. When plates moved in such a way that Antarctica became situated over the South Pole, it allowed a large land mass to cool and build up an ice sheet when then further cooled the climate by becoming a large reflective body of the Sun’s energy.
- The last 10,000 years have been relatively warm and this warm period within the Quaternary is known as the Holocene.
- It’s absolutely certain that the burning of fossil fuels and deforestation has caused an increase in global temperature.
Part 3: Tectonics, Weathering, Erosion and Soils
- The Earth’s crust is formed of moving plates; at the edges of plates earthquakes and volcanic activity are common.
- In the center of oceans new crust is formed; at the edge of oceans the crust sinks back into the mantle.
- Weathering by physical and chemical processes wears down rock. Climate and rock type are important controls of weathering process rates.
- Erosion transports weathered material by water, wind, and slow and fast mass movement.
- Soil is made up of minerals from weathered rock, organic matter, water and air. Soil formation is affected by climate, the parent material, topography and organisms.
- The texture of soil particles, structure and chemistry of a soil are crucial in determining its water and nutrient exchange capacity and hence its use for plant growth.
- Careful soil management is required as humans have degraded large areas of soil across the Earth through poor agricultural practice and pollution.
Part 4: Water and Ice
- Water evaporates from oceans, soil, living things (transpiration), rivers and lakes. At some point this water vapor condenses to water or ice in the atmosphere and returns to the Earth’s surface as precipitation. Some of this precipitation will infiltrate into the soils and rocks below the surface where it flows more slowly to river channels or sometimes directly to the oceans.
- There are four main stores of water. These are the world oceans, polar ice, terrestrial waters and atmospheric water. The oceans hold 93% of the water, polar ice holds 2%, the soils, lakes, rivers and groundwater hold 5% and the atmosphere holds a thousandth of 1% of water resources.
- Groundwater stores around 30% of the Earth’s freshwater (i.e. not salty). However, if this groundwater is to be available to supply river flow the rock or soil needs to be permeable, enabling water to flow through it. Layers of rock porous enough to store water and permeable enough to allow water to flow through them in economic quantities are called aquifers.
Part 5: The Geography of Ecosystems
- Biogeography is the term used to describe the geography of the biological world. It involves the study of the distribution and patterns of life on Earth and of the underlying processes that result in these patterns.
- The biosphere is the biological part of the Earth which incorporates the Earth’s surface and a shallow layer below it, the oceans and the lower atmosphere. Variations within the biosphere may result from factors including climate, geology, soil type, human action and biotic processes.
- A biome is a large area characterized by its vegetation, soil, climate and wildlife.