"This world may be only illusion -- but it's the only illusion we've got." --Edward Abbey

I. Life Through Time: Reading the Fossil Record

1. Charles Lyell: ". . . the present is the key to the past."
   1. It was becoming increasingly clear that the Earth was much older than anyone had suspected. (There had to be a lot of time to accommodate the growing number of extinct organisms, and the great changes in biodiversity.) How old, no one was sure. . .
   2. But how to interpret the rocks? Building on work by many other geologists, a 19th-century English lawyer-turned-geologist named Charles Lyell formulated the principle of uniformitarianism.
      1. This is a complex topic, because the word "uniformitarianism" has several different shades of meaning, most of which we're not going to go into.
      2. But in its modern form, it can be stated like this: Present-day processes, which can be observed now, can be used to explain past events. In other words:

         "The present is the key to the past."

      3. Example: You can go to, say, Hawaii, and watch molten lava cool and harden into black rock called basalt.
         
         Lava eruption and basalt at Pu'uo'o, Kilauea, Hawaii

         If you find similar rock elsewhere -- even if there's no volcano anywhere near -- it is most reasonable to assume that it was made by the same process.

      4. Other examples of this type of reasoning were in the slide show, such as the ripple marks in both beach sand at low tide and in ancient sandstone. . .
      5. There are times when geologists make exceptions. This is not an iron-clad law! But uniformitarianism is very good at generating testable hypotheses.

1. In 1831, British naval captain Robert Fitzroy was preparing a surveying and mapping mission to the coasts of South America.
   1. He took along a recent university graduate with a strong interest in biology and geology, by the name of Charles Darwin. . .
2. The Beagle sailed around the world, taking almost five years (1831-1836). Most of the voyage was taken up by surveying the coasts of South America.
   1. Darwin collected fossils in South America, and noticed that they seemed oddly similar to the living organisms that were, and are, native to South America. Example: The fossils of glyptodons and giant sloths look like giant versions of living armadillos and tree sloths.
3. On the home stretch, the Beagle briefly stopped at a few small islands about six hundred miles off the Pacific coast of South America: the Galàpagos Islands
   1. The Galàpagos Islands are volcanic islands -- some of the volcanoes are still occasionally active -- and they're relatively young compared to the mainland.
   2. These islands have many species that are unique to themselves -- but at the same time, that resemble South American species. Examples: prickly pear cactus trees; marine iguanas; giant tortoises, big enough to ride but still much like the gopher tortoises of the Americas; unique kinds of seagulls and mockingbirds. . . and many more.
   3. What's more, in many cases, different islands had different species.
      1. Example: Each island, and in some cases each separate mountain peak on the same island, has a giant tortoise with a differently-shaped shell.
      2. Example: There are fourteen species of finch on the islands, each of which feeds on a different food source and has a beak adapted to that food source.
   4. This raises the question: What is all this diversity doing here?
4. And back sailed the Beagle. . .