Geoscience - Geological Time Scale

Precambrian (Paleozoic)

4,600 Mya

-Makes up 85% of Earth’s history

-Few fossils, no hard body parts —> Earth’s natural processes erode fossils

-Crustal plates began to form: most of the rocks that formed have been eroded away, metamorphosed or recycled via subduction into the Earth’s interior.

-GOE- Great Oxygenation Event: Oxygen, produced by photosynthesis (by stromatolites, cyanobacteria) becomes abundant in the atmosphere

- Stromatolites are the most common Precambrian fossil

Cambrian (Paleozoic)

-It was the beginning of multi-celled organism life, otherwise known as the “Cambrian Explosion”

-Development of organisms that could secrete carbonate for the formation of outer skeletons - hard parts could be more easily fossilised

-Trilobites and brachiopods evolve, marking a significant increase in biodiversity and complexity of life forms.

Ordovician (Paleozoic)

-Large amount of coral appeared

-First appearance of vertebrates (animals with back bones) e.g jawless fish

Silurian (Paleozoic)

-Near the end, earliest known and plants and animals such as spiders and millipedes evolved on land.

Devonian (Paleozoic)

-Age of the fishes (first appearance of sharks)

-Fish slowly evolved into amphibians/tetrapods

-By the end of the Devonian, the first seed plants began to occur.

Carboniferous (Paleozoic)

-Means carbon-bearing —> widespread forests and swamps covered land, which were later fossilised as coal deposits

-Evolution of first reptiles

Permian (End of Paleozoic “ancient life”)

-Assembly of supercontinent Pangaea: shallow inland seas disappeared, many species of marine invertebrates go extinct

-Speciation of reptiles (therapsids= earliest mammal ancestors, diapsids= ancestors of dinosaurs, lizards, corocidles, snakes)

Permian Mass Extinction (Mesozoic begin, Paleozoic end)

• 95% of marine, 75% of terrestrial vertebrates become extinct

• Only known mass extinction of insects

• Eruption of Siberian trap flood basalts released massive amounts of CO2, causing an increase in global temp by 5*

• Increase in temperature of oceans and lowered O2 in the oceans led to release of methane from frozen methane hydrates. (bacteria flourished in anoxic water, releasing hydrogen sulfide)

Triassic (Mesozoic)

• Marked by the recovery of life after the Permian Mass Extinction, the first dinosaurs and mammals emerged, and warm, dry climates dominated the landscape.

• Development of triassic forests and marine life diversified.

Jurassic (Mesozoic)

• Known for the dominance of dinosaurs, the formation of large continental landmasses, and the emergence of the first birds. Marine life, including a diverse array of reptiles, thrived, while flowering plants began to evolve.

• Atlantic Ocean begins forming

• Reptiles like the Archaeopteryx start to dominate the skies

Cretaceous (last period of the Mesozoic: “middle life”)

• majority of well known dinosaurs existed in this period

• first flowering plants appear

KT Mass Extinction (Bleeds into Cenozoic)

• Evidence for meteorite impact:

  • Iridium signature - very low concentrations of Iridium on Earths’ surface, during differentiation event, most sunk to Earth’s core. Iridium is a rare element on Earth but is abundant in asteroids, so the presence of iridium in the sediment layer suggests that it was deposited by an asteroid impact.

  • Soot deposits worldwide directly over rich layer of Iridium suggest re-entry of rocks and meteorite pieces, blasted back into space

  • Shocked quarts (shocked from intense pressure) can only form when nuclear bombs explode or meteor impacts

  • Sink holes in Mexico define crater rim - sink holes generally form in areas of structural weakness

Tertiary Cenozoic “Recent life”

• Age of mammals begin

• Warm-blooded animals iwth fur more likely to survive ice-ages.

• Large carnivores evolve towards end (wolves, bears, cats)

Quarternary: Cenozoic “Recent Life”

• Early humans appear and complex societies develop

• Humans main cause of extinction of species (Tasmanian tiger, Dodo)

• Quarternary is in the present, (Anthropocene is under consideration to underline effect of Homo Sapiens on extinction of species)

Paleozoic

Pre-cambrian

Cambrian

Ordovician

Silurian

Devonian

Carboniferous

Mesozoic

Permian

Triassic

Jurassic

Cretaceous

Cenozoic

Tertiary

Quarternary