Evolutionary History of Life Flashcards
fossils
the preserved remains of organisms or traces (eg. footprints) or even organic compounds produced by them (chemical fossils)
hard parts fossilise more often
formation of fossils
buried in sediment which prevents bacteria decay
built up of sediment squeezes water out
compaction and chemical changes where sediment becomes rock
spaces in bone and wood are filled with minerals (heavier)
fossil moulds (impression) can fill with materials like silica and form fossil casts
trapped in amber
carbonisation: black shale is deposited on the ocean floor (little O2) and preserve soft parts as a thin carbon film on rock
relative dating
observing layers of sedimentary rock (stratigraphy)
- deepest = oldest
- compare depths
- often large scale events (volcano) spreads a sedimentary layer for comparison
- used for geological time scale
absolute dating
using radioactivity (half lives) and magnetic reversals
time scale
divided into eras and then periods by abrupt changes in the fossil record
precambrian
earth origin - evolution of first eukaryotes
palaeozoic
diversity of animals (Cambrian explosion) - permian extinction
mesozoic
ended with cretaceous extinction
cenozoic
to present day
plate tectonics theory
crust and part of the upper mantle (together lithosphere) are divided into plates that move, carrying biota with them
about 5cm per year
continental drift
oceanic ridges
where lava upwells
new crust of sea floor basalt moves apart on either side of a ridge
as sea floor spreads, continents on lighter (sialic) rocks move away
subduction
sea floor descends back into the mantle, forming deep-sea trenches
- lighter continents remain on the surface
- no part of the sea floor is older than 200 million years, been subducted
- trenches mark sites of earthquakes and volcanoes
hot spots
fixed points on the mantle where a column of hot basaltic lava rises
- as plates move over them, a chain of volcanic islands may form
types of plate boundaries
- move apart at ridges
- collide and one is subducted under another at trenches
- scrape past each other, causing deformations and faults
- collisions can create mountain belts
ancient positions of continents
- study past positions - rock magnetism, hot spots and magnetic reversals
- erosion and subduction destroy evidence (more than 20% of precambrian rocks lost, 90% of history)
rodinia
giant continent formed 1.2 billion years ago
750-800 million years ago it drifted to form 8 continents
super continents
500 mill ya: most landmasses at equator. Australia part of Gondwana and Europe part of Baltica
northern landmasses formed Laurasia and Gondwana went south
250 million years ago lausasia and Gondwana formed Pangea (inner area far from sea and very arid)
jurassic period: Gondwana split again and broke up 130 million years ago
precambrian era
- cherts and stromatolites
- chlorophyll
- organisms
archaean eon and proterozoic eon
cherts: fossils found in black chert (gels of silica) that precipitated on the ancient sea floor - oldest fossils are 3.3-3.5 billion year old cherts in WA (look like bacteria and cyanobacteria
stromatolites: fossils of concentrically layered rock - sediments trapped between layers of cyanobacteria (3.3-3.5 bill ya)
pristine and phytane (products of chlorophyll) and photosynthetic organisms
ironstones from 1.8-2.3 bill ya indicate oxygen became plentiful
prokaryotes and eukaryotes like green algae appear
ediacaran fauna: multicellular organisms
soft bodies organisms such as marine worms, jellyfish and anemone found as tracks, burrows and impressions 540-590 mill ya
all continents
short time before disappearing before shelly invertebrates in Cambrian
multicellular evolved in precambrian!
palaeozoic life: ancient life
251-542 mill ya
age of fishes and rapid evolution
mass extinction with loss of shallow seas
marine life:
- phytoplankton, zooplankton, trilobites (anthropods)
- shallow seas in ordovician - corals and molluscs
- jawless fish (ostracoderms) were the first vertebrates
- fleshy finned fish were related to first 4 legged vertebrates on land
terrestrial life:
- silurian (410 mill ya) earliest evidence of life on land
- amphibians in late denovian
- by end of palaeozoic, every major plant group had appeared (except flowering plants)
mesozoic life: age of reptiles
dinosaurs reigned but went extinct in cretaceous
dinosaur descendants, therapsids, gave rise to mammals
thecodonts were first bipedal
land habitats became available and mammals expanded (triassic)
cretaceous sudden radiation of flowering plants
cenozoic life: the beginning of modern life
65 mill ya to present
mammals and flowering plants become abundant
fossils of lineages related to humans date back at least 6 million years
biogeographic region
regions inhabited by unique forms of life
boreal region
northern fir forests (holarctic, palaearctic, nearctic)
palaeotropical regions
plants in africa, India and SE africa and animals
Ethiopian oriental
neotropical
South America, lower Central America
australian region
australia, PNG, new Caledonia and NZ
marine biogeographic zones
shallow water (shelf) and open ocean (pelagic)
continental shelf most diverse in tropics
bipolar distribution: one species living in arctic and the other in Antarctica
pelagic realm: planktonic organisms near surface, currents seperate species
prokaryotes diversification
found in rocks 3.77-4.28 bya
only inhabitants for 3 billion years - developed RNA, mitochondria, chloroplasts (oxygen was a poisonous waste product) and genes
singe celled eukaryotes
evolved from archael common ancestor - first eukaryotic common ancestor (resembled archaea)
1 billion ya FECA engulfed bacteria and formed a symbiotic relationship (ATP for Achaea and nutrients for bacteria). codependence resulted and genes were exchanged (mitochondria gets less). mitochondria gets cristae (increased SA)
evidence of endosymbiosis
double membrane (phospholipids are different on each layer) DNA - mitochondria has circular DNA similar to prokaryotes
cyanobacteria became
chloroplasts
multicellular eucaryotes
cells stick together
cells communicate
participate in a network of genetic interactions that regulate differentiation and division
cells can become specialised and can exceed size limits placed by diffusion, longer lifespan (cells die, not the organism)
earliest animals
dickinsonia (precursor to Cambrian animals) are small, oval, soft bodies marine organisms (571-541 mya)
diversification of animals
Cambrian explosion 13-25 mya
not many soft bodies fossils
molecular clocks: assuming DNA substitution rate is constant to determine age
colonisation of land
450 mya, plants and animals moved onto land (algae on soil)
algae already had genes needed to detect and interact with beneficial fungi (to get water) - allowed them to survive and evolve
animals like tiktaalik developed fins like legs and could move on land
oxygen and evolution
increases oxygen during precambrian period
evolution of large vascular plants increased oxygen (coal deposits and wildfires are evidence)
conquest of land by animals happened in two phases of high O2 concentration
oxygen forced evolution of animals (body size increased - gigantism - increased O2 diffusion especially across egg shell = big
decreased O2 led to oxygen
being the right size
small animals have resistance to falling
small organisms can walk on water
large animals pump blood further so larger blood pressure and tougher blood vessels
small organisms can diffuse when the limit is reached, SA is increased by gills and lungs
calculating SA
volume of sphere: 4/3pi r^3
SA of sphere: A = 4pi r^2
SA/volume
small
increased SA/V
efficiency of diffusion increases
calculating diffusion of oxygen
oxygen moves down the concentration gradient at a rate of J = D x (P0 - Pi)/T
J - rate of O2 movement
D - diffusion coefficient for environment
P0 - partial oxygen pressure outside cell
Pi - partial pressure inside
T - distance between two sides
when did oxygen spike?
410 mya, 290-300 mya
