IB Environmental systems and societies 3.1G Earth History and the Anthropocene Notes

Evidence of Evolution in the Rock Record

1. Earth is about 4.5 billion years old, and life has evolved gradually over that time.
2. Geological, climatic, and biological changes over millions of years shaped both the planet and its life.

The Fossil Record

1. Fossils are preserved remains in sedimentary rock, and their layers trace how species changed over time.
2. Transitional fossils capture the shift from one group of organisms to another.

Homologous Structures

1. Related species share the same underlying body plan, inherited from a common ancestor.
2. The pentadactyl (five-digit) limb is a classic example of divergent evolution.

Dating the Past

1. Carbon-14 dating measures radioactive decay to date relatively recent organic remains.
2. Ice cores trap ancient air, linking past atmospheres to climate and biodiversity.

The Geological Time Scale

1. Earth's history is divided into eons, eras, periods, epochs, and ages.
2. These divisions are defined by major biological and environmental changes, identified from fossils and radiometric dating.

The Four Great Eras of Life

1. Precambrian (4.6 billion – 541 million years ago)
   1. Formation of Earth and the earliest, mostly single-celled life.
   2. Cyanobacteria drove the Great Oxidation Event, which built the ozone layer and enabled complex life.
2. Paleozoic (541 – 252 million years ago)
   1. The Cambrian Explosion produced rapid marine diversification; plants and amphibians colonised land.
   2. Ended with the Permian mass extinction, the largest ever.
3. Mesozoic (252 – 66 million years ago)
   1. The Age of Reptiles, dominated by dinosaurs; early birds and mammals appeared.
   2. Ended with the K–Pg extinction that wiped out the non-avian dinosaurs.
4. Cenozoic (66 million years ago – present)
   1. The Age of Mammals; mammals and birds filled niches left by the dinosaurs.
   2. Humans (Homo sapiens) evolved late, in the Quaternary.

Mass Extinctions Reshape Life

1. A mass extinction is a rapid, global loss of a large fraction of species.
2. Earth has had five major mass extinctions, each followed by recovery.

Causes of Mass Extinction

1. Super-volcanic eruptions cause cooling or acid rain.
2. Meteorite impacts throw up dust that collapses food chains.
3. Tectonic movements, sea-level change, and climate shifts alter or destroy habitats.

The Five Major Extinctions

1. Ordovician–Silurian (~440 mya): about 85% of marine species lost.
2. Late Devonian (~375 mya): prolonged ocean anoxia.
3. Permian–Triassic (~252 mya): the 'Great Dying', up to 96% of marine species lost.
4. Triassic–Jurassic (~201 mya): volcanic activity during the break-up of Pangaea.
5. Cretaceous–Paleogene (~66 mya): an asteroid impact ended the non-avian dinosaurs.

The Sixth Mass Extinction

1. Humans are now driving a sixth mass extinction, faster than the previous five.
2. Current extinction rates are 100 to 1,000 times the natural background rate.
3. The main drivers are:
   1. Habitat destruction and deforestation.
   2. Climate change.
   3. Overexploitation of species.
   4. Pollution.
   5. Invasive species.

The Anthropocene: A Human-Dominated Epoch

1. The Anthropocene is a proposed epoch in which human activity is the dominant influence on Earth's systems.
2. It would follow the Holocene, which began about 11,700 years ago.

When Did It Begin?

1. 1610: a dip in CO2 after the collision of the Old and New Worlds (the Orbis spike).
2. 1950s: the Great Acceleration, with nuclear fallout marking sediments.
3. 1964: a carbon-14 spike from nuclear weapons testing.

Human Signatures in the Rock Record

1. Human activity is leaving planetary-scale markers in the strata:
   1. Plastic and chemical pollution, including a distinct 'plastic horizon' and persistent organic pollutants.
   2. Radioactive residues such as plutonium and cesium-137 from nuclear testing.
   3. Human-made materials such as concrete, aluminium, and plastics.
   4. Sediment change from damming, deforestation, and erosion.
   5. Global mixing of species far beyond their natural ranges.
2. Humans now move more sediment and rock than all natural processes combined, reshaping landscapes through mining, construction, and urbanisation.
3. These pressures are pushing several planetary boundaries and leaving permanent signals in Earth's record.