Lecture 2 Flashcards
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)
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
Name 6 ways in which fossilization can occur
Preservation of original material
Recrystallization
Carbonized films
Replacement
Permineralization
Dissolution
2 types of replacement
Phosphatization and pyritization
Permineralization synonym
Petrification
2 types of dissolution
Moulds and casts
Original material fossils
Preservation with little change to composition or structure
Examples of common original material fossils
Ice Age bones and teeth
Fossil shark teeth
Recrystallization
Mineral reorganization without dissolution
Example of recrystallization fossils
Polymorph minerals - slightly different crystal structure (e.g., CaCO3 as aragonite –> calcite)
Recrystallization as it relates to macrostructure and microstructure
Macrostructure not affected but reorganization/destruction of the original microstructure
Examples of specific organisms with recrystallization
Mollusc shells
Ordovician brachiopod shells
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
Replacement
The original material is completely replaced by a different material
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)
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
What is replacement through silicification often associated with?
Permineralization
Example of replacement through silicification
Alberta dinosaur bone
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
2 parts of permineralization
Permineralization
Replacement
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
