5C Flashcards
Age of earth
Earth is 4.5 billion years old
* unicellular prokaryotes by 3.5 billion
* multicellular life by 2.1 billion years ago
* complex multicellular animals by 650
million years ag
originally little oxygen - _______-atmosphere
* Oxidation prevented by ______ of ______ and
other ________ gases or ______ (water (H2O),
methane (CH4), ammonia (NH3) and hydrogen , (H2) as major components)
* _______ of energy (lightning) would transform these
into ______ compounds in ‘________ soup
originally little oxygen - reducing atmosphere
* Oxidation prevented by removal of oxygen and
other oxidizing gases or vapours (water (H2O),
methane (CH4), ammonia (NH3) and hydrogen
(H2) as major components)
* input of energy (lightning) would transform these
into organic compounds in ‘primordial soup
Early earth atmosphere - Urey Miller
experiment:
Experiment simulated the ______ ______
conditions and tested ______ origin of life
* __ of carbon was in ____ ___, __ of 22
used in living cells
* Still debate about Earth’s original
_________ and _______ molecules
present
Experiment simulated the early Earth
conditions and tested chemical origin of life
* 2% of carbon was in amino acids, 13 of 22
used in living cells
* Still debate about Earth’s original
atmosphere and reducing molecules
presen
was ocean environment actually reducing?
* Still pockets of ______ environments in the
deep oceans - _________ _____________
habitat
* has been suggested that ____ communities
might provide a model for _____ evolution of life
was ocean environment actually reducing?
* Still pockets of reducing environments in the
deep oceans - sulfur bacteria/ thermophiles
habitat
* has been suggested that vent communities
might provide a model for early evolution of life
Chemolithotrophy
Allows prokaryotes to maximize ATP production by using
different “food” source – i.e. different electron donors
Archaean - ________
Archaean - Proterozoic
4 billion - 510 million years ago
* Prokaryotes, Eukaryotes, Multicellularity
* Great oxygenation even
FIRST PROKARYOTES:
Oldest known specimens are from 3.2-3.4 billion years old, from _northern
Canada, South Africa and Australia
* Many are found in _________, where __________form a biofilm that
traps _______ __ _________
* Stromatolites appear in fossils dating to 2.7 billion years ago, decline in
abundance by 500 million years ag
Oldest known specimens are from 3.2-3.4 billion years old, from northern
Canada, South Africa and Australia
* Many are found in stromatolites, where cyanobacteria form a biofilm that
traps layers of sediment
* Stromatolites appear in fossils dating to 2.7 billion years ago, decline in
abundance by 500 million years ag
Cyanobacteria -
* By producing _______ oxygen as a byproduct of photosynthesis à
converted early ______ atmosphere into an ________ one (_______ of the
Earth)
* Dramatically changing the _________ of life forms on Earth by stimulating
biodiversity and leading to the near _____ of _____________
organism
Cyanobacteria (3 bya) : obtain their energy through photosynthesis
(cyano = blue)
* By producing gaseous oxygen as a byproduct of photosynthesis à
converted early reducing atmosphere into an oxidizing one (rusting of the
Earth)
* Dramatically changing the composition of life forms on Earth by stimulating
biodiversity and leading to the near-extinction of oxygen-intolerant
organism
- Free oxygen ________ in atmosphere
(__________), about 2.5 billion years ago,
with a huge increase 850 million years ago - Evidence….
- Free oxygen accumulates in atmosphere
(cyanobacteria), about 2.5 billion years ago,
with a huge increase 850 million years ago - Evidence:
- Banded Iron Formations abundant
between 2.5 and 1.8 billion years ago,
decline after - Major changes in number of rock types
formed after this event: hydrated and
oxidized mineral
Why the long gap before O2 atmosphere?
- probably long period of anoxygenic photosynthesis
- free oxygen reacted with ocean chemistry (not immediately released into
atmosphere) - Banded Iron Formations – oxygen was reacting with iron and sulphur to
form these rocks, common between 2.5 and 1.8 billion years ago - since Cambrian oxygen has been between 15-30% of atmosphere, high of
35% in Carboniferous
First eukaryotes
:
* _______ than prokaryotes; _______; ________
bound __________
* Endosymbiosis:
* ______+ _______ = eukaryote?
* mitochondria and plastids (e.g. _____)
were ___________ bacteria taken inside another
cell as an ___________ (~ 1.5 billion years ago
- larger than prokaryotes; nucleated; membrane
bound organelles - Endosymbiosis: origin of key eukaryotic
organelles result of symbiosis between separate
single-celled organisms - Archaea + bacteria = eukaryote?
- mitochondria and plastids (e.g. chloroplasts)
were free-living bacteria taken inside another
cell as an endosymbiont (~ 1.5 billion years ago
Evidence for endosymbiosis
- organelles are bound by membranes (just like
prokaryotes) - organelles have own DNA separate from DNA in
nucleus - mitochondrial DNA sequences similar to bacteria/
chloroplast DNA sequences similar to those of
some cyanobacteria - Reproduction: mitochondria replicate by pinching
Major episodes in the history of life
Paleozoic:
Ediacaran fauna:
Cambrian explosion; invasion of land; appearance of
gymnosperms; major groups of tetrapods
Ediacaran fauna
Lots of weird forms of
animals, now extinc
Cambrian explosion
- ________ appearance of many groups of
organisms about 530 million years ago - ________ by appearance of small ______ parts
- Unusually high number of sites with ____________ preservation (e.g. Burgess Shale)
- includes evidence of _________,
____________, and a large number of ______
forms - features of many modern groups appear:
______, __________,_______,_______
- rapid appearance of many groups of
organisms about 530 million years ago - preceded by appearance of small shell parts
- Unusually high number of sites with softbody preservation (e.g. Burgess Shale)
- includes evidence of arthropods,
echinoderms, and a large number of extinct
forms - features of many modern groups appear:
heads, mouths, eyes, legs
-_________ diversity likely present
* _________ O2 levels from ________ algae (allowing for _____ ______ rates,
______ body size, etc.)
* Evolution of _______, _________ of algal mats - opening of new _____
* Shift in ocean chemistry favoring ____________ __ ______ _______
Genetic diversity likely present
* Increasing O2 levels from eukaryotic algae (allowing for higher metabolic rates,
larger body size, etc.)
* Evolution of grazing, reduction of algal mats - opening of new niches
* Shift in ocean chemistry favouring production of calcium carbonat
Extinction and mass
extinction
* Normal ________ rate of extinction varies
but usually _ rate of speciation over time
* Mass extinction:
- Mass extinctions are _____
- Normal background rate of extinction varies
but usually ≦ rate of speciation over time - Mass extinction: rate of extinction greatly
exceeds rate of speciation (usually defined as more than 75% of known species in a
geologically short interval - Mass extinctions are periodic
Why are mass extinctions significant to
evolution?
- Niches are cleared/ ecological opportunities available
- leaves ‘dead clades walking’ - low diversity remnants of once diverse
lineages
