Lecture 2 Flashcards by Madelynn Hamilton

Do fossils change? Explain.

Fossils can continue to change as their host rocks undergo further modification within the Earth and on Earth’s surface (e.g., metamorphism, weathering)

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Fossil definition

The remains of an organism that have reached equilibrium with the geological conditions where they were preserved. This may take one year or 100,000 years, depending on the situation

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Name 6 ways in which fossilization can occur

Preservation of original material
Recrystallization
Carbonized films
Replacement
Permineralization
Dissolution

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2 types of replacement

Phosphatization and pyritization

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Permineralization synonym

Petrification

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2 types of dissolution

Moulds and casts

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Original material fossils

Preservation with little change to composition or structure

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Examples of common original material fossils

Ice Age bones and teeth
Fossil shark teeth

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Recrystallization

Mineral reorganization without dissolution

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Example of recrystallization fossils

Polymorph minerals - slightly different crystal structure (e.g., CaCO3 as aragonite –> calcite)

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Recrystallization as it relates to macrostructure and microstructure

Macrostructure not affected but reorganization/destruction of the original microstructure

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Examples of specific organisms with recrystallization

Mollusc shells
Ordovician brachiopod shells

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Carbonized films

Thin film of carbon represents modified remains of original material
Changed by removal of H2, O2, and N2 present in tissues and chitin, decomposition through anaerobic bacteria, and other processes

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Replacement

The original material is completely replaced by a different material

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Replacement through pyritization

The precipitation of pyrite requires:
Reactive iron and sulfate availability (sediment source)
Anoxia/hypoxia: Bacterial sulfate reduction-mediated decay (drives sulfides outwards into the sediment porewaters)

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Replacement through silicification

Porous tissues are infused with an aqueous silica solution
Progressive dissolution of structures - Si is deposited into the empty spaces
Transition to more stable forms of Si (opal - chalcedony - quartz) = very long process

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What is replacement through silicification often associated with?

Permineralization

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Example of replacement through silicification

Alberta dinosaur bone

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Permineralization (petrification)

Change of the chemical nature, without modification of the external shape - this can permit soft tissue preservation, and is a common type of preservation for fossil wood and bone

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2 parts of permineralization

Permineralization
Replacement

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Permineralization as the first part of the permineralization process

Solutions rich in minerals permeate porous tissues (e.g., bones, wood, shell) and precipitate to fill all empty spaces

Replacement as the second part of the permineralization process

The original hard parts are also removed by fluid flow, and replaced by a new mineral

Dissolution

Compaction, fluid flow, and heat can cause a shell or skeleton to completely dissolve, leaving a space within the rock

Mould

3-D negative imprint

Cast

Space is filled secondarily with minerals and produces a replica of the original organism

Implication of dissolution

Original material is gone Internal structures are lost, but the shape of the surface remains

Vast majority of cases of post-mortem processes

Taphonomic factors lead to a complete degradation Fossilization is NOT the default

Truly exceptional circumstances of post-mortem processes

Mineralization outpaces degradation Preservation of soft parts of organisms

Best-case scenarios for fossilization (name 4)

Rapid burial (limits biostratinomic processes) Fine-grained sediment (preserves fine details) Anoxic environment (limits decay) Aquatic environment (better protected from future erosion)

Systematics

Study of the diversification of living forms, and the relationships among living things through time

Phylogeny

Reconstruction of the evolutionary history of a group or groups of organisms, and their relationships

Taxonomy

The scientific study of naming, defining, and classifying groups of biological organisms based on shared characteristics

Classification

The process of grouping organisms based on their similarities

Relation between systematics and taxonomy

Disciplines of study

Relation between phylogeny and classification

Outcomes of systematic and taxonomic work

6 kingdoms of life

Bacteria Archaea Protists Fungi Plantae Animalia

Systematics orders

Subspecies Species Genus Family Order Class Phylum Kingdom Domain

Biological species

Organisms that share common characteristics Capable of interbreeding and producing fertile offspring Framed by the resources they depend on (ecological species) Capable of inheriting traits from one another within a common gene pool (genetic species)

Paleontological species

Organisms that share common morphological characteristics, sometimes behavioural evidence from fossils and traces For relatively "young" fossils (e.g., Ice Age), paleontological species may change with genetic findings Not possible to determine whether fossil organisms could reproduce with each other

How were geological periods first recognized?

From their fossil assemblages

How has the relationship between fossils and time been confirmed?

By other evidence, such as radioactive decay

How are the boundaries between periods defined?

By changes in fossils

2 broad categories of dating fossils

Relative or qualitative dating Absolute or quantitative dating

Relative or qualitative dating

Comparative dating using fossils (biostratigraphy) Order of formation of rocks based on field relationships (lithostratigraphy) --> youngest vs oldest

Absolute or quantitative dating

Radioactivity (radiometric methods) Molecular clock (timescale of evolutionary events) Actual age (or age range) can be established

Principle of original horizontality

Sediment layers are deposited horizontally, or nearly so, due to the effects of gravity

Law of superposition

Oldest layers are the deepest; youngest layers are on top

Absolute dating - radioactive decay

Decay from one chemical element to another; to a stable end result

Examples of absolute dating: radioactive decay

Radiocarbon (14C) dating (order of 50,000 years) U-Pb decay series (order of billion of years)

Molecular clocks

Describe the relationship between evolutionary rate and time, with the simplest clock model assuming that the rate of molecular (i.e., DNA) evolution is constant across species