The History of Life on Earth: Key Concepts and Events

Fossil Record

Shows macroevolutionary changes over time.

Terrestrial Vertebrates

First vertebrates adapted to land environments.

Photosynthesis Origin

Process that converts light energy into chemical energy.

Mass Extinctions

Significant loss of biodiversity in Earth's history.

Earth's Age

Earth is approximately 4.6 billion years old.

First Life Forms

Appeared around 3.8 billion years ago.

Small Organic Molecules

Basic building blocks for life, synthesized early.

Macromolecules

Complex molecules like proteins and nucleic acids.

Protocells

Membrane-containing droplets that may lead to life.

RNA World

Hypothesis that RNA was the first genetic material.

Ribozymes

RNA molecules that act as biological catalysts.

Oparin-Haldane Hypothesis

Suggests early Earth conditions favored organic compound synthesis.

Miller-Urey Experiment

Simulated early Earth conditions to produce amino acids.

Sedimentary Rock Strata

Layers of rock that contain fossil records.

Relative Dating

Determines age of fossils based on rock layers.

Radiometric Dating

Measures decay of radioactive isotopes to date fossils.

Half-life

Time for half of a radioactive sample to decay.

Tetrapods

Four-limbed vertebrates, evolved from ancestral synapsids.

Geologic Time Scale

Chronological dating of Earth's history in eons.

Phanerozoic Eon

Current eon characterized by abundant fossil records.

Endosymbiosis

Theory that eukaryotic cells originated from prokaryotes.

Endosymbiont Theory Evidence

Includes replication by binary fission and circular DNA.

Origin of Multicellularity

Occurred approximately 1.2 billion years ago.

Snowball Earth Hypothesis

Extreme glaciation that confined life to equatorial regions.

Cambrian Explosion

Rapid diversification of life forms 535-525 million years ago.

Colonization of Land

Fungi, plants, and animals moved onto land 500 million years ago.

Continental Drift

Movement of Earth's continents over geological time.

Pangaea

Supercontinent that existed around 250 million years ago.

Adaptive Radiation

Rapid evolution of species to fill ecological niches.

Heterochrony

Evolutionary change in the timing of developmental events.

Paedomorphosis

Retention of juvenile traits in adult organisms.

Homeotic Genes

Regulatory genes that control body plan development.

Hox Genes

Specific homeotic genes influencing body structure organization.

Exaptations

Structures evolved for one function but adapted for another.

Complex Eyes Evolution

Evolved independently from simple light-sensitive cells.