Chapter 3 | Geologic Record

Geologic Record

Way of dividing time into different intervals

Eons

Hadean, Archaeon, Proterozoic, Phanerozoic

Eras

Paleozoic, mesozoic, cenozoic

Periods

Within eras

5 key events

1. Evolution of prokaryotes, eukaryotes, & oxygen

2. Multicellularity

3. Cambrian explosion

4. Colonization of land

Hadean eon (4.6 — 4.0 BYA)

Origin of the Earth & rocks

Archean eon (4 — 2.5 BYA)

• Prokaryotic life formation

• Bacteria & archaea split

• Evolution of cyanobacteria

Stromatalites

Form in shallow seas, layers of rock and bacteria (cyanobacteria) fossilized

Oxygen Revolution

• Spike of oxygen concentration ~3 BYA

• Extinction of anaerobic life

• Caused by abundance of cyanobacteria & photosynthesis

Proterozoic eon (2.5 — 0.542 BYA)

• Organelles & mitochondria

• Originated by endosymbiosis

Endosymbiosis

• Two cells merging into one

• Proposed by Lynn Morg

• First mitochondria (serial endosymbiosis)

Evidence for endosymbiosis

• Genetic sequence data

• Genetic material found in chloroplasts & mitochondria

• Closest relatives are free-living bacteria

• Compare plasma membranes

• Ribosomes are like bacterial ribosomes

• Multicellularity

Symbiotic multicellularity

Organisms form one organism, sharing two genomes

Clonal multicellularity

Same species joining together allowing for specialization

Edicaran biota (570 MYA)

First complex multicellular organisms

Phanerozoic Eon

1. Paleozoic

2. Mesozoic

3. Cenozoic

Cambrian period (541 — 485 MYA)

• Modern phyla evolving

• Bilateral animals

• Evolution of Hox gene

• Hard-bodied animals

• Adaptations for predation

• Chordates

Hox gene

Sets the body plan of animals, with modifications in those genes determining modifications of the body

Ordovician period

• Complex chordates — vertebrate lampreys, cephalopod diversification, coral diversification, arthropods colonize land

• First recognized mass extinction of marine invertebrates

Silurian period (443 — 416 MYA)

• Plants & animals move to land

• Terrestrial plant diversification, simple branching pattern

• Fungi

• Invertebrate animals

• Vascular plants

Devorian period (416 — 359 MYA)

• Increased predation and competition creating muscular, hard-bodied fish

• First trees forming

• Arthropod diversification

• First amphibians

• First terrestrial vertebrates - tetrapods

• Transitionary characteristics

Tiktaalik fossil

“Fishopod” — characteristics of both fish & tetrapod

Carboniferous period (359 — 299 MYA)

• Woody plant tissue allows first tries to grow using lignin

• No bacteria to break down the carbon produced by trees yet

• Coal deposits & other fossil fuels formed in terrestrial environments

• Amniotic egg separates reproduction on land/water

Permian period

• Land masses collected in Pangea

• Amniotic eggs separate reproduction from water

• Stem/early reptiles & mammals

• Plants evolve seeds (gymnosperms), reproducing without water

• Mass extinction (P-T Permian-Triassic)

Permian Mass Extinction

• Volcanic eruptions produced greenhouse gases, creating a hot climate (CO₂)

• CO₂ moves into the water causing oceans to acidify — corals die

• Less sunlight on the surface due to soot in the air — cooling effects

• Increases bacterial growth, decreased oxygen levels → extinction of some fish

Dimetrodon

Early sphenacodontid that gave rise to mammals, part of the synapsids

Synapsids

Species united by the opening in the skull that attaches the jaw muscles

Mesozoic era (251 — 66 MYA)

• 3 periods

• Break up of Pangea, forming modern continents

Triassic (252 — 201 MYA)

• Formation of large coral forests

• Diversification of gymnosperms — cycads & ginkgoes

• First true dinosaurs — archosaurs

Jurassic (201 — 145 MYA)

• Pangea continues to break up

• Pterosaurs — Diopsids

• Theropod dinosaurs — birds

• Therian mammals → true mammals diversify

• Conifers dominate (gymnosperms)

Cretaceous (145 — 66 MYA)

• Angiosperms dominate, coevolution with arthropods

• Meteorite/volcanic mass extinction (75%)

Cenozoic Era (66 MYA — Present)

Tertiary

• Paleogene

• Neogene

Quaternary

• Pleistocene

• Holocene

• Anthropocene

Paleogene (65.5 — 23 MYA)

Modern placental mammals originate, fill niches lost by dinosaurs

Neogene (23 — 2.58 MYA)

• Australopithecus (early hominid) evolved in Africa

• Homo genus

• Mammals dominate

Pleistocene (2.58 — 11k YA)

• Ice age

• Megafauna

• Homo sapiens evolve → extinction of pleistocene mammals from ice age and hunting

Holocene (11k YA)

Mass extinction

Anthropocene (1950 — 2000s)

Human dominated epoch

Mass extinction rate

• 1 species/year/million species

• Elevated by 1000x driven by volcanic & human activity

5 mass extinctions

1. End of Ordovician

2. End of Devonian

3. End of Permian

4. End of Triassic

5. End of Cretaceous