Changes in Species Over Time

Key Knowledge

  • Changes in species over geological time can be seen through:

    • Fossil records.

    • Faunal succession.

    • Index and transitional fossils.

    • Relative and absolute dating of fossils.

  • Speciation occurs due to isolation and genetic divergence:

    • Allopatric speciation (e.g., Galápagos finches).

    • Sympatric speciation (e.g., Howea palms on Lord Howe Island).

Geological Time

  • Geological time: Chronological dating relating geological strata to time.

  • Earth's age: Approximately 4.5 billion years.

  • Geological time scale:

    • Eons → Eras → Periods → Epochs → Ages.

  • Relative age: Age of an object compared to another.

  • Absolute age: Age of an object in actual years.

Changing Life Forms Over Time

  • Early Earth: Dominated by prokaryotes.

  • Later: Increase in diversity with plants, animals, fungi, and protists.

  • Key events in geological time:

    • 45004500 Mya: Earth formation.

    • 38003800 Mya: First prokaryotic cells.

    • 600600 Mya: First multicellular eukaryotes.

    • 479479 Mya: First vertebrates (jawless fish).

    • 365365 Mya: First land plants.

    • 130130 Mya: First mammals.

Types of Fossils

  • Fossils: Evidence of past life.

  • Palaeontology: Study of fossils.

  • Types of fossils:

    • Physical fossils: Remains of structures.

    • Trace fossils: Evidence of activities.

    • Biosignatures: Inferred evidence.

Physical Fossils

  • Mineralized fossils: Organic material replaced by minerals.

  • Fossil impressions: Impression of structure.

  • Preserved organisms: Complete preservation in amber, ice, or tar.

Trace Fossils

  • Evidence of organism activities (footprints, burrows, etc.).

Biosignatures

  • Physical or chemical signs inferred from past life (e.g., stromatolites).

Formation of Fossils

  • Fossilisation: Preservation of organism parts from the geological past.

  • Conditions for fossilisation:

    • Rapid burial in sediment.

    • Alkaline, oxygen-depleted, or anoxic conditions.

    • Very cold environments.

  • Most often hard tissues are preserved.

  • Moulds and Casts: Organism decays leaving cavity (mould), which gets filled (cast).

Evidence from Fossils

  • Fossil record: Supports the Darwin-Wallace theory of evolution.

  • Predictable sequence of life forms in the fossil record.

    • Ancestral species appear before descendant species.

Faunal Succession

  • Fossil succession: Sedimentary rock strata containing fossilised fauna and flora are arranged vertically in a specific manner.

  • Organisms appear in a consistent order.

Index and Transitional Fossils

  • Index fossils: Geologically short-lived, widely distributed species in restricted rock strata.

  • Transitional fossils: Intermediate forms between ancestral and descendant groups (e.g., Archaeopteryx, Tiktaalik).

Dating Fossils

  • Relative dating:

    • Stratigraphic method: Oldest stratum at the bottom.

    • Faunal succession: Using index fossils.

  • Absolute dating:

    • Radiometric dating: Based on radioactive decay.

    • Half-life: Time for half the radioactive isotope to decay.

    • Carbon dating: For organic remains up to 60,000 years old.

    • Potassium-Argon dating: For igneous rocks.

Speciation

  • Speciation: Formation of new species.

  • Species definition: Organisms that can interbreed and produce fertile offspring.

  • Isolating mechanisms:

    • Pre-zygotic: Prevent mating.

    • Post-zygotic: Prevent fertile offspring.

Allopatric Speciation

  • Geographic isolation leads to genetic divergence.

  • Example: Galápagos finches.

Sympatric Speciation

  • Speciation without geographic isolation.

  • Example: Howea palms on Lord Howe Island.