Fossils and Their Formation

What are Fossils?

• Preserved remains and traces of organisms over 10 000 years old.
• Found in rock.

Types of Fossils

• Trace fossils: Footprints, trails, burrows, and coprolites (fossilized dung)
• Moulds: Impressions left by an organism.
• Casts: Formed when a mould is filled with mineral rock (mineralisation).
• Trueform fossils: Shells, teeth, and bones.

How do Cast Fossils Form?

• Fossils form under very specific conditions.
• An animal dies and its skeleton is buried quickly by sediment.
• The sediment hardens, turning to stone.
• Groundwater dissolves the skeleton, leaving a mould.
• Minerals from the groundwater crystallise inside the mould, forming a cast.
• Erosion exposes the fossil on the Earth's surface.

Conditions for Fossilisation

• Absence of decomposers
• Absence of oxygen and water
• Low temperatures

Fossil Evidence for Evolution

• The fossil record provides strong evidence for evolution.
• Imagine a puzzle with 9/10 pieces missing; becoming a fossil is highly unlikely.
• Many factors can prevent an organism from being fossilized, or a fossil from being found.
• Shows changes in structure over time.
• Organisms in the fossil record have become more complex over time.
• For example, the progression from unicellular organisms to invertebrates to vertebrates.
• More recent (younger) fossils resemble organisms living today.
• The variety of fossils increases in the upper, more recent layers of rock.
• No fossil record exists of any modern living plants or animals.
  • Have they avoided being fossilised or evolved?
  • This suggests that organisms found as fossils either became extinct or evolved into species currently living.
• Missing links – the common ancestors provide strong evidence for evolution
  • For example, Archaeopteryx is considered a transitional fossil between dinosaurs and birds.

Evolutionary Biology

• The study of how life on Earth has changed over time
• Emphasizes processes like natural selection, mutation, and genetic drift

Natural Selection

• The driving force behind adaptation in organisms
• Individuals with advantageous traits are more likely to survive and reproduce
• Over time, these traits become more common in the population

Mutation

• Changes in DNA sequences that introduce new traits
• The source of genetic variation within a population
• Mutations can be beneficial, harmful, or have no effect

Genetic Drift

• Random changes in allele frequencies within a population
• More significant in smaller populations
• Can result in the loss of genetic diversity

Speciation

• The process by which new species arise
• Allopatric speciation: occurs when populations are geographically isolated
• Sympatric speciation: occurs within the same geographic area, often due to polyploidy or habitat differentiation

Evidence for Evolution

• Fossil Record: Shows changes in species over time, including transitional forms
• Comparative Anatomy: Homologous structures (similar structures, different functions) indicate common ancestry; Analogous structures (similar functions, different structures) indicate convergent evolution
• Molecular Biology: Genetic similarities between species reveal shared ancestry
• Biogeography: The distribution of species reflects their evolutionary history

Key Figures

• Charles Darwin: Proposed the theory of evolution by natural selection
• Alfred Russel Wallace: Independently developed a similar theory
• Modern Evolutionary Synthesis: Combined Darwinian natural selection with Mendelian genetics

Applications of Evolutionary Biology

• Understanding antibiotic resistance in bacteria
• Conservation biology practices to protect genetic diversity
• Agricultural practices like selective breeding and GMOs

Contemporary Research Areas

• Evolution of social behaviors
• Evolutionary developmental biology (evo-devo)
• The impact of climate change on evolution

Explore the fascinating world of fossils, including their types and how they form. This quiz delves into trace fossils, molds, casts, and trueform fossils, along with the conditions necessary for fossilization. Additionally, uncover the role of fossils in providing evidence for evolution.