 Greetings! Behind me you can see the Nittany Valley State College and the Penn State campus and I just want to point out to you that you can see a mix of land uses including the town and forest and agricultural fields. Prior to European colonization of North America this region would have been entirely forested including that valley behind me. In 2007 when I began teaching Earth 530 I didn't make an introductory video for Unit 6 on the biosphere and thus here we are in 2014 making that video. Much has happened in the interim. For example Earth's population has grown by 500 million people to over 7 billion total people living on earth. Much of society has begun to recognize the degradational effects of human activities on the landscape. Let's consider an example. You likely recall that I am a geologist thus this example I will provide of humanity's effect on the critical zone is from the geological literature. A study from 2005 by Bruce Wilkinson. Look at the graph in front of you and notice that on either one of the y-axis is described annual loss of sediment and soil either measured in tons or in meters per million years. On the x-axis you can see time from the present on the right to 2000 years before present on the left. The solid black line crossing the graph shows a long-term average natural erosion rate calculated by various means through geologic time. What you should notice then is that in the open diamonds is shown that's this cumulative effect of erosion by human processes. Early on in humanity's history this is primarily by agriculture and as you move from the left to the right of the diagram following those open diamonds you'll see that the rate increases and that increases as a function of agricultural activities as well as industrial and construction activities. The point of this graph is that if you compare this open diamond at present to the solid black line crossing the graph showing natural erosion rates you should notice that there's an orders of magnitude shift in humanity's erosive effect to values that now exceed long-term natural rates by as much as 50 times. I want to stress what I just said the combined effects of humanity at present now erode and transport more solid material on earth's surface than all natural processes combined. Our 7.1 billion people move more dirt than all wind streams rivers and glaciers combined. Thus in this unit 6 when we consider biotic effects on the critical zone we cannot ignore humanity. Throughout the semester you've been exposed to various topics associated with human degradation of the critical zone. In lesson 12 you will focus on this topic to provide some talk some context. In unit 6 we will consider topics of biodiversity and ecological processes and ways in which landscape scale character is this characterization of biotic attributes may be considered. Life on earth can be classified into six kingdoms. Of these kingdoms most people are familiar with the plant and animal kingdoms. Kingdoms are further subdivided and the finest level of that subdivision is species. To give you some perspective on numbers some estimates suggests that 8.7 million species exist on earth and that means that up to 90% of life on earth has yet to be discovered. Each organism may play a unique role in its ecosystem and therefore may impact the critical zone in a unique manner. Let's consider some examples. We've hiked about two miles on this glorious July day to this clearing in the Rothrock State Forest. The clearing is here due to a combination of human and invasive species but the continued presence of the clearing, the maintenance of it if you will, is due to colonization by Allegheny mound ants. In the background here you can see at least three ant mounds and those mounds range in size from three to four feet in diameter and two to two and a half feet high. Let's have a closer look. The Allegheny mound ants are known to create mounds up to ten feet in diameter and five feet high with tunnels that extend to similar depths below ground. In the process of building the mounds the ants churn the soil thus introducing fresh mineral matter from depth to the more intensive weathering environment at the surface. Their tunnels increase soil porosity thereby providing pathways for water and gas transfer deeper into the soil than otherwise would be possible. The ants also inject formic acid into nearby vegetation thus killing it an easing expansion of the colony. Here you can see a halo of dead blueberry branches surrounding this active colony. Here you can see an abandoned colony that's six feet in diameter and up to two and a half feet high. We can tell it's abandoned because it's now vegetated by mosses and grass. The resident black pear population likes to eat the ants and their eggs which may explain the presence of this crater in the top of the once thriving colony. The sound you hear is from hundreds of thousands of cicadas that have erupted from the landscape during these few weeks approaching summer solstice. Another example of life interacting with the critical zone. The cicadas emerge from soil burrows churning the soil and introducing mineral matter from depth to the surface. Notice the pen for scale. The burrows also increase soil porosity thereby providing pathways for water and gas transfer deeper in the soil profile than might otherwise be possible. The combination of molted larval exoskeletons and dead adult cicadas may also periodically introduce a new source of organic matter to the surface litter of the forest floor and o-horizon of the forest soil. The first example was from the animal kingdom and now I'd like to consider what for most of you is going to be a less obvious effect of the plant kingdom. If a tree falls in the woods does it matter? Here beside me you can see a fallen deciduous tree and you can also see that the root mass of that fallen tree has incorporated large pieces of rock and sediment and soil. What geologists call tree throw. In this process the tree rips up the substrate and churns the soil aerating an otherwise subterranean realm and setting off a cascade of changing geochemical and ecological processes. In a typical Appalachian mountain setting this process can entirely overturn a landscape in a few thousand years. On a slope the effect can be relatively dramatic. In the Appalachian mountain region a typical hill slope away from the erosive effects of a stream erodes primarily by gravitational processes that geologists call creep. Creep is the slow downward slide of loose soil mantle on top of a more compacted and less mobile zone of soil and rock. Detailed studies of the rates of sediment and soil movement and erosion by tree throw demonstrate that tree throw erodes at a rate that is at least two orders of magnitude greater than creep. Thus in temperate regions of earth like the Appalachian mountains trees are the dominant erosive force on the landscape other than humans. I hope these examples have demonstrated that the biosphere interacts with the critical zone in unique ways that may not be immediately obvious to most people. As you study the biosphere in unit 6 and consider the critical zone near your home or school remember this complexity and value it. A topic we will also consider in this unit 6.