These notes include Interlude E

Interlude E: Memories of Past Lives: Fossils and Evolution

The Discovery of Fossils

• Sedimentary rocks contain fossils.

  • Shells, bones, leaves, footprints.

• Fossils: the remnant or trace of an ancient living organism that has been preserved in rock or sediment after lithification.

• Paleontology: the study of fossils.

• Paleontologists: scientists who study fossils.

• Evolution: the progressive change over time in characteristics of species that has led to the appearance of new species.

Fossilization

What Kinds of Rocks Contain Fossils?

• Fossils are found in sedimentary rocks.

• Fossils are sometimes found in tuff (volcanic ash).

• Fossils are destroyed by the metamorphism process.

Forming Fossils

• Fossilization: the process of forming a fossil.

Many Kinds of Fossils

• Frozen or dried body fossils

  • The entire body of an organism may be preserved.

  • Permafrost is permanently frozen ground.

    • Mammoths.

  • Desiccated organisms are dried out and can be preserved.

• Body fossils preserved in amber or tar

  • Insects may get trapped in sticky sap or resin, which later hardens into amber, and preserves the insect.

  • Organism can sink into tar and cause their bones to be preserved.

• Preserved or replaced bones, teeth, and shells

  • Bones and shells are contain durable minerals which may survive in rock.

  • When not stable, they may recrystallize. The shape of the bone or shell can be preserved.

• Molds and casts of bodies

  • Materials pressed into soft sediment leaves a mold (ex: shells).

    • A mold appears as an indentation into a bed of rock.

  • Cast: Sediment that preserves the shape of a shell, it once filled before the shell, dissolved or mechanically weathered away.

    • A cast protrudes from the surface of a bed of rock.

• Carbonized impressions of bodies

  • Impressions: flattened molds and casts produced when soft or semisoft organisms are pressed between layers of sediment.

  • Chemical reactions eventually remove the organic material, leaving only a thin film of carbon on the surface of the impression.

• Permineralized fossils

  • Permineralization: the process by which minerals precipitate in porous material, such as wood or bone, underground.

  • Petrified wood: wood that has undergone permineralization and has turned into agate. During the process, the cell walls of the wood transform into organic films that survive permineralization.

• Trace fossils

  • Trace fossils: footprints, feeding traces, burrows, and dung that organisms leave behind in sediment.

• Chemical fossils

  • Living plants or animals consist of complex organic chemicals.

Fossil Preservation

• It takes special circumstances to produce a fossil and for a fossil to survive over geologic time.

  • Oxygen content of the depositional environment.

  • Rapid burial

  • The presence of hard parts

Window to the Past

• Extraordinary fossils: A rare fossilized relic, or trace, of the soft part of an organism.

Taxonomy and Identification

Organizing Life

• Taxonomy: the study of how to classify organisms in a systematic way.

• Taxonomists divide all life into three domains:

  • Archaea

  • Bacteria

  • Eukarya

• They differ from one another due to the characteristics in their DNA.

• Archaea

  • Include tiny single celled microorganisms

• Bacteria

  • Also includes tiny single celled microbes.

• Both Archaea and Bacteria are prokaryotes (their cells do not contain a nucleus).

• Eukarya, the domain of eukaryotes, organisms whose cells contain a nucleus, are divided into kingdoms.

  • Protista

  • Fungi

  • Plantae

  • Animalia

• Each kingdom consists of one or more phyla.

  • Each phylum has classes, and it continues to break down from here.

Identifying Fossils

• Morphology: form or shape of a fossil.

• Not all fossils resemble living organism.

The Fossil Record

A Brief History of Life

• Cambrian explosion: the remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period. 

• Phylogeny: the evolutionary relationships among organism.

• Phylogenetic tree: a chart representing the ideas of paleontologists showing which groups of organisms radiated from which ancestors.

Is the Fossil Record Complete?

• Paleontologists have not not sampled every cubic centimeter of sedimentary rock exposed on the Earth.

• Not all organisms are represented in the rock record, because not all organisms have a high preservation potential.

• The sequence of sedimentary strata that exist on the Earth does not account for every moment of time at every location since the formation of our planet.

Evolution and Extinction

Darwin’s Grand Idea

• Darwin made detailed observations of plants, animals, and geology in the field, and he amassed an immense specimen collection from South America, Australia, and Africa.

• According to Darwin’s hypothesis, when a population of finches became isolated, it gradually developed new traits.

• Darwin referred to the survival of the fittest as natural selection, because it occurs on its own in nature.

• Theory of evolution by natural selection: the idea that species change over time, new species appear, and old, species disappear, due to the survival of the fittest.

Extinction

• Extinction: occurs when the last members of a species dies.

• Geological factors among many phenomenon can cause extinction:

  • Global climate change

  • Tectonic activity

  • Asteroid or comet impact

  • Voluminous volcanic eruptions

  • The appearance of a new predator or competitor

• Biodiversity: the overall variation of life.

Chapter 10

10.1: Introduction

• Geologic time: the span of time since the Earth’s formation.

10.2: The Concept of Geologic Time

Setting the Stage for Studying the Past

10.3: Relative Age

10.4: Unconformities: Gaps in the Record

10.5: Stratigraphic Formations and Their Correlation

10.6: The Geologic Column

10.7: How Do We Determine Numerical Ages?

10.8: Numerical Age and Geologic Time