A few thoughts on extinction...
My usual line is, if I give a lecture on extinction (and while this is not specifically a lecture on extinction, there is extinction in it) -- is that we have to have some murder -- so it's going to be a good story. [tape is blank for a while due to an electrical outage. During this period, a brief review was given of the age of the Earth and the repeated occurrence of background and mass extinction therein. While the Earth is 4.6+ billion years old, and life is 3.5-3.8 billion years old, most of the focus on the lecture will be on the last 400 Million years, as it is in this point that life flourished on land.]
I'm back live. Life (on land and otherwise) is contingent upon the very organisms that Karl was talking about...plants (a favorite bumper sticker of mine asks, "Have you thanked a green plant today?)" Certainly, we understand plants as autotrophic organisms that give us the foods that we eat and that capture the sun's energy. Whether you are a vegetarian or you are a carnivore, ultimately, it is plants that give you energy. This permits the diversity of animals, this gives us the diversity of life on earth. While we generally tend to think of plants as food, plants are important in other ways too. They create environments. They modify earth climate. They create three-dimensional space, a three dimensional space in which much of the diversification of animal life takes place. So, plants are significant to our very existence - without them, we would not be here.
What I propose to do today is to trace the history of plants. I am going to focus specifically on terrestrial plants because we are terrestrial organisms. Very few of us poke our heads under water. I haven't poked my head under water enough. I could tell you a story about the evolution of plants in an aquatic environment and how they influence other aquatic plants, marine invertebrates, marine vertebrates, etc. But, I am going to focus on the terrestrial portion of the planet because that is what we are most familiar with. This is what your students are going to be most familiar with. So, let's move and first set the stage as it were.
Look at the diversity of kinds of habitats on the present earth:
they range widely from the spruce biome on the one hand, to a tropical environment,
to a temperate forest
or to the great grasslands of the central portions of the continent, Africa, Asia, South America, North America.
Each of these possesses different plant structure and diversity, each of them supports a different kind of animal life. A diversity of habitats even occurs within a small area of the Earth, by example, the diverse habitats such as we have in California, from the oak woodlands that make California so beautiful, to the spring wild flowers that dominate this spring in particular because of the extraordinary rains that we have had.
From the montane forests and the chaparral lands, there is an enormous diversity of plant life harboring an enormous diversity of animal life.
Even in the areas of apparent harshest environment of the present day, we find specialized organisms that are living in these environments. This is what we are used to. This is what we think of when we think of the Earth, what we think of the animals and the plants on Earth. But it wasn't always thus. No.