1-1 Earth Systems Science and Environmental Geology

The key thing to understand about the Earth as a system is that while there is effectively no exchange of matter with other celestial bodies, there is an extraordinary amount of exchange of matter and energy within the various systems of the Earth (e.g., between the atmosphere and oceans). Much of that exchange is driven by the energy we receive from the sun, but energy from within the Earth is also an important driving force, especially over geological time.

Some of the more obvious interactions that take place all around us are summarized on Figure 1.2.1 in the textbook. Almost all of these interactions involve water in some way. That might be the flow of water as rain or streams or underground, but it also includes the massive amount of water moved through the atmosphere in the form of water vapour, as well as the transfer of substances suspended or dissolved in water. Movement of water in the form of ice is also important.

As shown on Figure 1.2.2, by far the greatest volume of water flow on Earth is via evaporation from the oceans and rain back down into the oceans. The annual volume of river flow into the oceans is less than 10% of the amount rain that falls on the oceans, and the flow of groundwater to the oceans is less still. It is also important to note that the volume of water transferred from land to the atmosphere—by evaporation and by transpiration from plants—is greater than the volume that flows into the oceans and rivers. Most of that transfer (about 90%) is by direct evaporation (from the ground and from lakes and rivers), and the rest is by transpiration from plants.

Although there are many ways that water moves, it also remains within some reservoirs for very long periods. This is illustrated on Figure 1.2.3.  Water is held within plants, the atmosphere and in rivers for only weeks, on average, but in glaciers (because they remain frozen) and the oceans (because they are vast) for thousands of years. Groundwater deep within the crust moves extremely slowly and can remain there for millions of years. Not shown on Figure 1.2.3 is the water contained within minerals in rocks, some of which can remain locked up for hundreds of millions, or even billions, of years.

The key roles of the sun in various Earth Systems processes are illustrated on Figure 1.2.5.  Solar energy drives water movement through evaporation and ocean currents (and wind currents as described in Box 1-1 below), but it also powers the growth of plants, heats the surfaces of the Earth directly—and then the atmosphere indirectly—and contributes to geological processes like weathering.

Box 1-1 What is an Atmospheric River?

In November of 2021 the residents of southern British Columbia and northern Washington became very familiar with the term “atmospheric river”, as wave after wave of moisture-laden air flowed in from the Pacific, bringing devastating floods, slope failures and other disasters to the region (more on that later in this course). Figure 1-1 shows the moisture and cloud pattern from a similar but less powerful atmospheric river in January 2020. The intensity of the blue and green colours is proportional to the amount of moisture being transported (as water vapour and water droplets). According to NOAA, a strong atmospheric river can transport water at a rate between 7 and 15 times the flow of the Mississippi River.

An atmospheric river is a graphic illustration of the Earth system in action, as it represents the transportation of water onto land. That same water then flows off the land bringing massive amounts of sediments and dissolved constituents into the ocean. The river flows of November 2021 in southern British Columbia would also have transported parts of peoples homes and other belongings, plus ripped up vegetation and the carcasses of thousands of farm animals, out into the ocean.

The construction of mountains is critically important to Earth Systems because it enhances the rate of erosion and weathering. Weathering plays a role in controlling the climate by consuming carbon dioxide from the atmosphere and transferring it to the ocean and eventually into ocean sediments. While the sun is, by far, the major driver of Earth systems, the Earth’s internal energy also plays an important role. Some of the critical internally-driven processes are illustrated on Figure 1.2.6. They include mantle convection, which drives plate tectonics, and therefore contributes to plate collisions and mountain building, volcanism (which contributes water and important gases to the atmosphere) and subduction (which moves geological and other materials from the surface back into the mantle).

Figure 1.2.6 doesn’t show the Earth’s core, where the convective motion of liquid iron generates the Earth’s magnetic field. The magnetic field is critical to life on Earth as it deflects the charged particles of the solar wind (that would have stripped away our atmosphere by now without a magnetic field) and protects us from harmful cosmic radiation.

As noted in the Declaration on Earth System Science (Box 1.3 in the textbook) and illustrated on Figure 1.2.7, the Earth System can be changed significantly by human activities, and there is no shortage of evidence that this is happening now. The current most serious consequence of human activities is that we are changing the climate, but other consequences include destruction and poisoning of ecosystems on both land and in the oceans, destabilization of slopes, and disruptions to surface water systems. These other consequences are all made worse by climate change.

Section 1.3 of the textbook provides a brief overview of the topics that are covered in Environmental Geology. Please review that carefully, as it will give you an idea of where we are going in this course, and how many of the different topics that we’ll be covering relate to one another.