Diversity Of Life On Earth Flashcards
What is the Hadean period?
- 3800 MYA
- harsh conditions, high temp
- V high CO2 liquid water due to high atmospheric pressure of CO2
- No evidence of life but basic chemicals present
- Formation of complex organic molecules
What happens and when in the Archaean eon?
3800-2500 MYA
- few island much ocean
- Heat flow = 3x that of today but cooling
- V high Co2, negligible oxygen until end of eon
- first prokaryotic life forms with self-replication all marine
——- Key to evolution = photosynthetic Cyanobacteria generating O2 as a waste product of chemically splitting water.
—— provided enough O2 for evolution of oxidation reactions as the energy source for ATP synthesis.
- O2 toxic for most prok
> soon after 1500 MY marine eukaryotes appear and diversify.
> late proteozioic especially ‘edicaran’ period 635- 542 MYA evidence of substantial diversity of complex, multicellular marine animals. Origins are therefore earlier, but not preserved.
What happened in the Cambrian explosion? When was it?
- 488-542 MYA
- O2 Conc approaching current levels
- COntinents come together to form several land masses especially Gondwana.
- Rapid diversification of animal groups
- Almost exclusively Maine fauna/flora nothing on land.
What where the fauna in the Cambrian period?
Many sponges, cnidarian so, worms, molluscs and arthropods
- Several fossil beds show good preservation
- First evidence of vertebrates at the end of the Cambrian.
When was the Ordovician period? What happened?
488-444 MYA
- Continued marine evolutionary radiation but little changed on land or freshwater- lacked multicellular plants.
- Strong radiation of molluscs (including large Cephalopoda) brachiopods and echinoderms.
- At the end of the Ordovivian as massive glaciers formed over Gondwana, sea levels dropped, waters cooled and 75% of animal species become extinct.
What happened in the Silurian period and when was it?
- 44-416 MYA
- Marine life rebounded from the mass extinction at the end of Ordovician. Marine verrtebrates in the form of jawless fish become abundant.
- First terrestrial Vascualr plants, with roots and leaves, appeared late in Silurian giving vegetation in and around freshwater.
- First terrestrial arthropods- scorpions, millipedes appeared.
What happened during the Devonian period and when was it?
- Northern land mass or Laurasia and Gondwana move towards each other.
- 416-359
- Early period warm and humid
- there is a great radiation of corals, shelled Cephalopoda and jawed fish.
- Jawed fish become increasingly dominant predators so most jawless become extinct.
- 75% of all marine species are extinct
Explain how territorial communities developed in the Devonian period?
- club mosses, horsetails and tree ferns became increasingly common.
- Plants with roots accelerated weathering, generating forest soils.
- SOme of the earliest wind pollinated plants formed.
- First known centipedes, spiders, mites and insects
- fishlike amphibians began to occupy land at the end.
What was the Carboniferous period and when?
- 359- 297 MYA
- Climte began to warm but large glaciers formed over high-lattitude Gondwana. Extensive forests grew in tropical areas.
What were the Carboniferous fauna?
- DIversity of terrestrial animals greatly increased.
- Snails, scorpions and insects were abundant and diverse.
- Flight evolved in insects giving them access to tall plants and increased dispersal potential.
- Amphibians became better adapted to life on land with greater capacity for free movement on land- all were carnivorous mostly eating invertebrates.
What heppened in the Permian period and when was it?
- 297-251 MYA
- continents coalesced into the supercontinent Pangaea.
- Diverese animal fauna: most modern insects groups and evolution of one line of amphibians to the reptile amniotes, with well protected eggs that can be laid on dry land.
- Massive volcanic activity towards the end of the period. Ash blocked sunlight and the climate cooled resulting in the largest glaciers.
- Atmospheric O2 declined from 30-12%.
- MOST DRAMATIC mass extinction in Earth’s history in all environments- around 96% of species were lost.
When was the Mesozoic Era and the Triassic?
- 251-200 MYA
- As Pangea slowly separated into individual continents, sea level rose and re-flooded continental shelves forming inland seas.
- O2 levels slowly rose again. Life diversified, but from a different starting point.
- New-seed baring plants (e.g. Conifers)
What happened during the Triassic radiation?
- Widespread radiation of marine and freshwater fauna from residual taxi.
- Great diversification of reptiles began giving rise to dinosaurs, crocodiles and mammals (end of Triassic) and birds (end of Jurassic).
> end of Triassic was marked by and other mass extinction perhaps due to a meteorite.
What happened during the Jurassic period and when was it?
- 200-145 MYA
- Land divided into Lurasia to north and Gondwana to south.
- Ray finned fish diversify massively from their previous ‘false start’
- early mammals diversified
- ## first birds
What happened during the Cretaceus period and when?
145-65 MYA
- L & G separated and started to break appart further, with continuous sea thoughout the tropics.
- High sea levels; earth warm and humid
- Increaed sea diversity
- First radiation of flowering plants.
What happened at the end of the Mesozoic era?
- Mass extinction at the end of the Cretaceous during which much marine, freshwater and terrestrial life perished. ALL dinosaurs became extinct.
- Evidence for massive environmental change, probably at least partly due to meteorite impact.
- Wildfires raged through the tropics + sea level also fell.
What happened in the Cenozoic Era- tertiary period?
- 65-1.8 MYA
- continental position approximated to what they are today.
- Early tertiary was hot and humid but became cooler and drier.
What happened in the tertiary?
- Flowering plants diversified and came to dominate all but the coolest regions. Mammals, birds, snakes lizards and insects diversified greatly.
What happened in the quaternary period when was it?
- 1.8 MYA to now
- Dramatic cooling and climate fluctuations during the Pleiostocene with 4 major ice ages- last retreated from temperate areas
How diverse is life on Earth today?
- 8.7 million species of terrestrial/freshwater eukaryotes.
- Less clear for prokaryotes.
What are the 3 domains an their fundamental molecular differences?
- BACTERIA = Prokaryotes, ester
- ARCHAEBACTERIA = Prokaryotes, ether
- EUKARYA = Eukaryotic, ester
What were Jean-Baptiste Lamarck’s thoughts
- All organisms have innate power to progress towards a more complex and perfect form. Could improve by their own inherent ability (a God given facility).
- Inner disposition causing the performance of actions sufficient to meet needs of the changing environment
- Characters acquired through me use, transmissible from one generation to another e.g. Giraffe’s neck
What were Darwins main propositions?
- Randon, heritable variation exists within species.
2. Variation occurs without any reference to the needs of the organism.
3. Large, abrupt changes are rare- usually without gradual continuous changes away from original form.
4. Small variations whcih improved fitness are maintained and increased in frequency within the population by natural selection
5. Limited resources > struggle for existence > survival of the best fitted
What were the 2 weaknesses in Darwins theory?
- Time for evolutionary change
2. Heritability mechanisms
