MODULE 14:ORIGIN & HISTORY OF LIFE + EXTINCTION

How did life originate according to modern hypotheses?

Life began as self-replicating molecules capable of capturing energy and copying themselves, eventually forming protocells made of nucleic acids, proteins, and lipids.

What evidence suggests all life shares a common ancestor?

Universal use of L-amino acids, the genetic code, DNA replication, protein synthesis, and shared basic metabolic pathways.

What is the RNA world hypothesis?

The idea that early life was based on RNA molecules that could both store information and catalyze reactions, enabling self-replication.

How could protocells form in the RNA world?

RNA molecules can catalyze the formation of lipid membranes, creating simple cell-like compartments.

How did proteins likely evolve from RNA systems?

Ribozymes used cofactors combining amino acids and small oligonucleotides; these structures eventually became ribosomes, tRNAs, and proteins.

Does uncertainty about the origin of life undermine evolutionary theory?

No, because evolutionary theory explains diversity after life originated, not the initial spark itself.

What is radiometric dating?

A method using the half-life of isotopes (e.g., C14) to estimate the age of rocks or organic material.

What is molecular clock dating?

Estimating divergence times using mutation rates and genetic differences, calibrated with fossils or geological events.

Why are divergence time estimates uncertain?

All dating methods produce confidence intervals rather than exact ages.

What characterized life during the Precambrian?

Low oxygen, dominance of Archaea and bacteria, and extensive lateral gene transfer among early lineages.

When did oxygen levels rise significantly on Earth?

About 2.4 billion years ago, due to the evolution of photosynthesis.

When did eukaryotes first appear?

Approximately 1.5 billion years ago, with large cells and endosymbiotic organelles like mitochondria and chloroplasts.

What are Ediacaran fauna?

Soft-bodied early animals (around 640-600 mya) with simple radial or bilateral forms, poorly understood.

What major event marks the early Paleozoic?

The Cambrian explosion, a rapid diversification of complex and skeletonized animal forms.

What innovations appeared during the Cambrian explosion?

Larger body sizes, limbs, skeletons, complex body plans, and nearly all major animal phyla.

What factors may have caused the Cambrian explosion?

Changes in regulatory genes, increased oxygen, novel ecological interactions, and key morphological innovations.

How have continents and climates shaped life through the Mesozoic and Cenozoic?

Shifting land masses and climates changed geographic ranges and opened or closed ecological opportunities.

What is adaptive radiation?

Rapid diversification of one lineage into many species occupying different ecological niches.

What conditions promote adaptive radiation?

Ecological opportunity, morphological innovation, and access to unexploited resources.

What is macroevolutionary stasis?

Long periods where lineages show little net morphological change but still fluctuate around an average.

What are mass extinctions?

Rapid, global extinction events affecting many taxa; during the Big 5, over 60% of species went extinct.

What is background extinction?

The normal, constant rate of extinction within clades over time, varying among groups.

What caused the KT extinction?

A 15 km asteroid impact supported by iridium layers, crater evidence, and shocked minerals.

What were the consequences of the KT impact?

Acid rain, climate change from atmospheric dust, wildfires, tsunamis, and collapse of food webs.

Which groups were most affected by the KT extinction?

Dinosaurs and many marine organisms; meanwhile mammals, turtles, insects, and amphibians largely survived.

What biological signal appears in plants after the KT impact?

A spike in fern spores, indicating ecosystem collapse followed by pioneer species.

How do modern human activities compare to past extinction drivers?

Humans act as a "meteorite," causing extinctions via habitat loss, invasives, exploitation, and climate change.

How much higher are modern extinction rates than background rates?

Approximately 100 to 1000 times higher.

Examples of human-driven extinctions

Dodo, moas, and numerous island bird species.