Unlocking Earth's Secrets: A Guide to Fossils, Geological Time, and the Origin of Life

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What Evidence Do Rocks Provide About Life?

Rocks are still an important source of information about many forms of life that existed on this planet.

Why Can Scientists Not Be Sure How Earth Was Created?

Because no rock dates to the formation of the Earth.

How Might Fossil Teeth Reveal an Animal's Diet?

Size and shape indicate diet.

Explain Relative Dating of Fossils

Sedimentary rocks form layers, with newer or younger layers added on top of older layers. This does not tell scientists the exact age of the fossil; however, it does tell the scientist the fossil's age in relation to others above it or below it.

Two More Common Radioactive Isotopes

  • Potassium-40
  • Carbon-14

What Is a Mass Extinction?

It is when many organisms disappear from the fossil record at the same time.

What Does the Explosion (Paleozoic) Refer To?

Refers to the huge quantity of new life that appeared during the Paleozoic Era.



  • May be bone, tooth, or imprint
  • Provide information about the variety of life in the past
  • Can provide information about ancient climates

Geological Time Scale

  • Divided into eras
  • Eras are further divided into periods
  • Divisions based on the kind of organisms that lived then


  • Humans are large mammals that appeared in the Cenozoic Era
  • The theory of plate tectonics explains how continents move
  • Most fossils are found in sedimentary rocks
  • Scientists use radiometric dating

The Origin of Life

What Did Francesco Redi's Experiment Prove?

That maggots do not come from spontaneous generation; they come from flies.

Describe How Pasteur Developed the Concept of Biogenesis

Pasteur used a specially designed glass bottle that allowed air to enter the bottle but kept microorganisms out. There was a broth with nutrients in the bottle.

What Two Things Had to Happen Before Life Could Appear on Earth?

  1. Organic molecules were present
  2. They formed into more complex molecules

What Happens When Amino Acids Are Heated?

They become proteins.

What Were Two Results of Oxygen in the Atmosphere?

  1. Organisms that use oxygen evolved
  2. An ozone layer was created

Mini Glossary

  • Oceans contain organic molecules
  • Protocells develop
  • Prokaryotes appear
  • Organisms use chemosynthesis
  • Organisms use photosynthesis
  • Ozone layer develops
  • Complex organic molecules form

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