Biology : Semester II


IntroductionSection 1 | Section 2 | Section 3 | Section 4 | Section 5

  Section One:

Part 1 | Part 2 | Part 3 | Part 4

Biology : History of Life on Earth : Part One


Fossils are any evidence of past life. This is a very broad definition that includes the standard shells, bones, petrified wood, and leaves. However, there are many more things that can become fossils: footprints, pollen, feeding traces, worm burrows, even feces. Scientists have begun to study fossil DNA and other biochemical remains. Fossils can range from miniscule bacteria to behemoth dinosaurs that must have shaken the ground as they walked. Aside from the beauty of their patterns and textures, fossils tell us about what the life of the past looked like, and in some cases, how it lived and behaved.

lab notebook Internet Fossil Collection Lab Notebook:10 points

Internet fossil collection. In your notebook begin a fossil collection by searching the Internet for images and information about fossils. Don’t just gather pictures, get information about the type of creature this fossil was, the age of rocks from which the fossil came, and the location where the fossils are from.

The ancient Greeks thought fossils were the remains of once-living creatures. During the Middle Ages fossils were viewed as artifacts the Devil put there to tempt people's faith. The seventeenth century work of Italian scientist Leonardo Da Vinci and Danish anatomist Nicholas Steno (1638-1686) finally led to the widespread recognition of fossils as the remains of creatures, many of which varied quite noticeably from living creatures alive today.

We divide fossils into body fossils and trace fossils (also known as ichnofossils). A body fossil is a part of (or in some cases the entire) body of the creature. In some rare cases the organic material of the creature remains in the fossil, but more often we get casts and molds that reveal the external and internal structure of the organism, but not original material. Trace fossils do not reveal much information about the anatomy of the creatures that made them, but instead offer glimpses of the activity and physiology of the creature.

There are several types of body fossils that differ in the mode of preservation of the original material of the organism. Compressions form when the overlying sediment "compresses" the organism into a flat layer. This results in some of the original organic material of the creature being preserved, often as thin carbonaceous films. However, many times the organic material is further decayed, leaving only a "part and counterpart" detailing the external form of the creature. Casts and molds are a type of preservation where the original material decays leaving a mold in surrounding rock that can be filled with another sediment (cast). Casts can be external or internal, the latter being known as steinkerns. Petrifaction is the literal "turning to stone" by replacement of organic matter with silica. Petrified wood forms by this process.

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