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Evolution, ecology and behaviour > History of Life > Flashcards

History of Life Flashcards

1
Q

When did the earth form?

A

4.5 billion years ago

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2
Q

Where did life first evolve?

A

Possibly the earths early oceans but evidence was destroyed by asteroids

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3
Q

What is the evidence for 1st life forms and what does it suggest?

A

3.7bya- chemical composition of sedimentary rocks suggest 1st primitive unicellular life forms appeared

3.7bya- 1st stromatalites appeared

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4
Q

what are stromatolites?

A

sedimentary formations created by photosynthetic microorganisms

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5
Q

What were the conditions like on the Archaean earth?

A

Lethal to humans nowadays:
- Intense UV radiation
- lots of cyanide
- anoxic atmosphere- very little oxygen
- Atmosphere was mostly CO2
- Very little land- land formed when volcanos poked out of oceans

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6
Q

What are the conditions of the Archaean earth ideal for?

A

spontaneous formation of organic molecules

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7
Q

What were the 1st life forms considered to be + what are they?

A

Heterotrophs = can’t make own food so needs to feed on organic matter- multicellular organisms

Autotrophs = can make their own food- plants and algae

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8
Q

How did the 1st life forms make/get their food?

A

Heterotrophs- used rhodopsins to break down organic molecules

Autotrophs
- utilised high levels of hydrogen + CO2 to produce methane and release energy- known as methanogens
- Photosynthesis evolved using hydrogen sulfide as substrate- this was replaced by cyanobacteria with water and released oxygen

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9
Q

Describe the stages of how oxygen became more abundant in the atmosphere

A
  1. Great oxygenation event- caused by cyanobacteria via photosynthesis = free O2 in atmosphere but levels still only 10% of present day
  2. Boring billion years- oxygen production + consumption cancelled each other out
  3. Lands + oceans absorbing oxygen were filled so the atmosphere began accumulating oxygen
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10
Q

What did the increase in oxygen levels result in?

A

1st soft bodied metazoans appeared in the fossil record
- prokaryotes were predominant until evolution of eukaryotes that made use of oxygen levels for growth and fed off of stromatolites

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11
Q

What are metazoans?

A

multicellular organisms with differentiated tissues

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12
Q

What was the key step that helped more complex organisms emerge?

A

evolution of flagellum for movement and feeding

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13
Q

What were the features of the complex organisms that emerged and in what period were they present?

A

Present in the Ediacaran period:
- flagellum
- Bilaterally symmetrical bodies

= ancestors of most modern animals

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14
Q

What are rangeomorphs and when were they present?

A

Present in Ediacaran period:
= flat, blade-shaped animals that are now extinct- most likely due to being easy prey or relying on high nutrient levels

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15
Q

What happened after the 1st metazoans appeared in the fossil record and what is it defined by?

A

The Cambrian explosion- defined by the sudden appearence of skeletal fossils in the fossil record where the 1st metazoans dramatically diversified

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16
Q

Why did the Cambrian explosion happen?

A

Still debated:

higher O2 levels allowed for the evolution of carnivores, which provides a different selection pressure so organisms had to adapt to avoid predation:
- motile predators evolved mechanisms to attack e.g. teeth
- Shells + skeletons appeared in response as defence mechanisms + hiding

Oceans became more alkaline due to run-off from sediments from unhabited land = shells formed as a by-product

17
Q

What type of feeders were Cambrian species?

A

Generalist

18
Q

When did specialised feeders evolve?

A

Ordovician period

19
Q

What happened in the Ordovician period and why?

A

Further wave of diversification as animals had to adapt due to selection pressure of being fed on in different ways:

  • First jawed fish evolved
  • Plants colonised land and atmospheric CO2 levels fell due to increased weathering of rocks
20
Q

Describe how the number of genera changed from the Cambrian period and why?

A

Number of genera of marine fossils has risen and fallen but never fell below Cambrian levels- this is due to mass extinctions occuring:

  1. End of Ordovician
  2. End of Devonian
  3. End of Permian
  4. End of Triassic
  5. End of Cretaceous
21
Q

Name an example of a cambrian species

A

Trilobites

22
Q

What were Cambrian species replaced by and what were their origins?

A

fauna categorised as Modern or Paleozoic but all had origins from Cambrian species

23
Q

How much marine life was lost over the 3 mass extinctions?

A

85%

24
Q

Describe the rates of evolution and extinction

A
  • Most species survive 5-10my
  • Recovery after extinction (evolution) takes 10-40my
  • Many ecologists believe we’re in the 6th mass extinction- driven by human activity and is expected to take 10-40my to recover
25
Q

What % of extinction do mass extinctions make up?

A

4%- 96% of extinction happens outside of these events

26
Q

What are evolutionary radiations? and define the 3 broad triggers

A

= sudden rise in diversity in a group due to selection pressures:

  • Extinctions = removing the species occupying a certain niche allows for a new one to dominate in new environment
  • Innovations = new traits opens up a niche space
  • Invasion of a new habitat = new resources to exploit
27
Q

What did evolutionary radiations lead to?

A

The colonisation of land

28
Q

How long did it take multi-cellular life to colonise land and when was land more diverse than the oceans?

A

It took 500my and land became more diverse in the mid-Cretaceous

29
Q

What were the 1st multicellular organisms on land and when did they appear?

A

fungi-lichen (= fungus + bacteria) appeared in Ediacaran

30
Q

What were the challenges organisms faced when transferring from ocean to land?

A
  • body support as relied on water for buoyancy
  • Dehydration
  • Gas exchange in air
  • Highly variable temperatures in comparison to oceans
  • Lack of dissolved nutrients in floating water
31
Q

How were these challenges overcome?

A

Organisms had to evolve in water first

32
Q

Describe the evolution of plants from water to land

A
  1. 1st plants likely in swamps and marshes
  2. Evolved to protrude from water
  3. Spores appeared in fossil record which provides evidence that plants were using aerial dispersal
  4. This likely required a symbiosis with fungi which were already present on land
  5. Vascular plants appeared 435mya with transport tissues
33
Q

What are some examples of features of plant evolution?

A

+ Innovations like woody stems and roots caused replacement of groups that lacked them
+ Resistant to extinctions as many can survive damage in form of seeds

34
Q

What effects did plants have on animal evolution?

A
  • Plant tissue formed a large new food resource
  • Rotting plant tissue in water reduced dissolved O2
  • Photosynthesis increased atmospheric CO2
35
Q

What effects did animals have on plant evolution?

A
  • Herbivores prompted evolution of plant defences
  • Plants used insects to pollinate their flowers- more efficient than wind
  • Seed dispersal via fruit and nuts that attract animals
36
Q

How did coal form?

A

Lignin in plant tissues was indigestible for fungi/animals = vast amounts of biomass piled up = coal formed and this process has not been repeated since

  • Atmospheric O2 was at its highest (35%) which induced coal beds
37
Q

Describe what animals on land were like

A

Arthropods were pre-adapted for moving on land as they had waterproof shells + legs- footprints left in late silurian and appearing in fossils in Devonian but they were not consuming plants

vertebrates were intially air-breathing fish in shallow water but crawled to land to:
- bask and digest
- lay eggs in warm inland pools away from predators

38
Q

Describe the evolution of humans

A

in Africa hominids arose and diversified from 5.5mya and one species were able to spread to Eurasia and continued to spread

Evolution, ecology and behaviour (14 decks)

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