Lecture 3- A Brief History Of Life On Earth Flashcards
What are the 6 kingdoms of life on earth
- archaea, eubacteria, protists, fungi, plantae,animalia
Out o f the six kingdoms, which are eukaryotes
Protists, plantae, animal, fungi
Out of the six kingdoms, which are prokaryotes
Archaea, eubacteria
Describe archaea
Prokaryotes lacking peptidoglycan cell walls
Eg. Methanogen
Describe eubacteria
-Prokaryotes with peptidoglycan cell walls
Eg. Cyanobacteria, pathogens
Describe protists
Eukaryotic singular celled organisms. Are either heterotrophic or photosynthetic
Describe fungi
Eukaryotic mostly multicellular organisms (except yeast). Heterotrophic and commonly non motile with chitin cell walls
Describe plantae
Eukaryotic multi cellular, non motile organisms
-photosynthetic (eg. Tree)
Describe anamalia
Eukaryotic, multicellular, motile, heterotrophic
Which as the four eukaryotes are motile?
Anamalia and some fungi
What is the key difference between archaea and eubacteria?
The presence of a peptidogloycan cell wall
How old is the earth?
4.5 billion years
Describe atmospheric conditions on the early earth
Extremely hostile, reducing atmosphere that allowed for the formation of carbon rich compounds and provided little protection against UV rays. This was incompatible to most life
What was the first types life to evolve when??
Prokaryotes 3.8 billion years ago. They dominated life from 3. 8- 2 billion years ago
When did Cyanobacteria first begin evolving?
- 5 billion years ago
What impact did Cyanobacteria evolution have on atmospheric composition?
They raised Oz concentration (as they are photosynthetic) about 2.4 billion years ago in the great oxygenation event
What happened to the oxygen released by Cyanobacteria (what did it form)
Free oxygen immedi ally dissolved into surrounding waters, and when its concentration within these waters was sufficient, it precipitated out as iron oxide. This accumulated in sediment in alternating with chert, forming banded iron formations
What happens when the oceans became supersaturated with oxygen
It began to gas out and changed atmospheric composition
When did the great oxygenation event occur?
It began with the evolution of Cyanobacteria around 2.7 billion years ago, but peaked 2.4 billion years ago
What was the first evidence of life on earth?
Stromatolites found in Australia. Stromatolites from when Cyanobacteria colonies group together, so provided the first evidence for life on earth
What were the impacts of the great oxygenation event?
Raised atmospheric oxygen levels over billions of years, formed the ozone layer which protects the earth from harmful UV rays, made conditions more favourable to many forms of life
What impact did the great oxygenation event have on the already present prokaryote populations (besides Cyanobacteria)
In pure form, oxygen attacks chemical bonds and can inhibit enzyme growth and damage cells. This was toxic to many prokaryotes, causing a large die off
How did organisms react to the great oxygenation event?
They had to adapt their physiology quickly in order to survive, such as evolving to use respiration as their main source of energy
When did Eukayotes first evolve?
Between 1.5 and 2.1 billion years ago, although there is evidence of them existing in 2.7 billion year old shale
How do eukaryotes differ from prokaryotes?
They have an endoplasmic recticulum,membranes,nulcelus,chloroplast,mitochondria and a well developed nuclear envelope. In contrast, prokaryotes lack membrane bound organelles and store dna in plasmids
Which three forms of life are thought to have diverged from a com ancestor?
Modern eukaryotes, archaea bacteria and eubacteria are all thought to have evolved from a common ancestor prokaryotes
How are eukaryotes thought to have evolved?
Via endosymbiosis
How does endosymbiosis occur(simply)
A prokaryote would’ve engulfed a smaller cell (called an endosymbiont) and instead of dissolving it, this smaller life form would become an organelle performing functions within the host. The two would become one organism over time
What endosymbiont formed modern day eukaryote mitochondria?
Aerobic heterotrophic prokaryote
What organism is thought to have formed chloroplast in modern day eukaryotes?
Cyanobacteria
What is the evidence that mitochondria and chloroplast formed organelles via endosymbiosis?
They are similar to bacteria in size and replicate by splitting in half. They also have dna for some of their components that replicates when the cell divides and genes are transcribed in the organelle- NOT the nucleus.
Why did endosymbiosis occur?
Due to the great oxygenation event, the world became aerobic around 2.4 billion years ago. An anaerobic prokaryote would’ve benefitted from a symbiotic relationship with an aerobic prokaryotes, as it would’ve had the ability to carry out OXIDATIVE METABOLISM. The acquisition of Cyanobacteria would’ve given the prokaryote nutritional independence
What feature do aerobic prokaryotes have that an anaerobic prokaryote would’ve required in order to survive in an aerobic world?
An oxidative metabolism
When does the first evidence of multicelluarly date to?
1.8 billion years ago
When did large and diverse multicellular organisms evolve?
600 million years ago
How did diverse multicellular organism evolve?
Single called eukaryotes living in close proximity lead to the development of specialised cells and sexual reproduction. Sexual reproduction cause GENETIC VARIATION, and increased rates of evolution.
What are the edicaran biota?
The first group of complex, multicellular organism. They lived 630-541 million years ago
How does sexual reproduction lead to genetic variation?
Gamete fusion allows for genetic recombination, variation occurs, selection acts on it and evolution follows
What were the next eukaryotes to evolve (after multicellular ones)
Jellyfish and worms, around 600 ma
What important event occurred 35g-325ma?
The Cambrian explosion
When was there a large increase in eukaryote diversity?why?
570 ms, as it was the end of an ice age (conditions became more favourable )
When did plants and fungi colonise land?
500 ma
Give the dates of the five mass extinctions, and how much life was lost
Ordovician Silurian mass extinction: 440 ma. 50% of animal families
Devonian Carboniferous: 355 ma. 30% animal families
Permian Triassic. Approx 250 ma. 60% animal. 95% marine
Triassic Jurassic. 205ma. 35% all Life
Cretaceous tertiary. 65ma. 50% animal families
What is adaptive radiation?
After mass extinction events, many ecological niches that were previously occupied become available. Surviving species diversify rapidly to fill these niches
How long did it take for marine species to recover after the Permian Triassic mass extinction?
- Million years
When did mammals undergo adaptive radiation? Why?
After the Cretaceous tertiary mass extinction, as they no longer had to compete for resources with dinosaurs.
