How has the Earth changed Flashcards
Oxygenation event
2.8billion yrs ago (began slightly 3.8Ga)
cyanobacteria and photoferrotropes began to produce O2
O2 reacted with Fe in sea to produce FeO which settled to produce banded iron formations
2.3billion yrs ago
o2 enter atmosphere
changed atmosphere
reacted with methane
Photosynthesizers removed CO2 from atmosphere
temp drop
mass glaciation (Huronia)
mass extinction
poisoned most anaerobic organisms
produce ozone layer
what is a snowball earth
when Icesheets surround earth - only happened 2-3x
How do snowball earths occur
CO2 removed from atmosphere due to eruptions of basalt + produces SO2,
Particles block sun –> solar diming
leads to cooling
in the long time to greenhouse gases heat and undo ice age
(increased photosynthesis also decreases CO2)
CO2 levels throughout geological time
peaked in the Cambrian- 7000ppm
then decreased slowly till about 250million yrs ago when it rose again till 150ma
then decreased till modern day with us now having some of the lowest levels ever
implications of CO2 on climate and sea levels
Recent : high CO2 levels = hot climate and high sea levels (as less H2O stored as ice)
positive feedback loop
Over time however temperature hasn’t necessary followed the same trend as CO2 - might not be main effector of climate
What was earth’s early atmosphere + why?
originally H + He when solar system formed –> then light gases escaped
then became CO2 dominated due to volc activity (similar to venus) –> similar to Hawaiian volc emissions
Some H2O vapour, N, NH3 and CH4
little O2
H20 condensed to form oceans about 4Ga –> mostly CO2 left in atmosphere
What is a greenhouse earth + when did it last occur?
when the global temperature is hotter than average + no continental glaciers
warm periods
last in early tertiary 33.9Ma
What causes greenhouse earth?
can be:
increased solar radiation reaching earth
or changes in gas concs in atmosphere
or volcanic eruptions—> greenhouse gases over time raise temp
breakup of continents associated with greenhouse conditions
What is an icehouse earth? + when was the last?
Colder than usual- lower average global temps
icecaps and glaciers on continents- large continental icesheets at poles
currently in one
What causes an icehouse earth?
caused by increased reflection of solar radiation back to space (albedo effect)
+ volc events - release sulphate aerosols reflect back solar radiation
cooling
often linked to aggregation of continents
e.g. Pinatubo eruption in 1991 decreased temp of northern hemisphere 0.6 degrees
Eustatic definition
Sea level changes due to changes in vol of ocean basins or vol of H2O in them
these changes can be seen worldwide
also thermal expansion of H2O as seen at MOR/ ice melting
Isostatic definition
Sea level changes due to uplift or subsidence of cont crust.
often sinks when loaded with ice/ sed and rises when load removed
only seen in affected region
only appears to change doesn’t actually
e.g. Scotland undergoing isostatic rebound –> beaches look raised
What is the phanerozoic
Most recent Eon of time (current)
when life became complex
Cambrian to Quaternary
~500Ma - 0Ma
what happened to sea levels over the phanerozoic
as the temperature increased so did sea level
rose from Cambrian to Ordovician peaking mid Ordovician at the highest it has even been
then decreased till the breakup of Pangea in the early Permian
then began to rise again till it peaks mid cretaceous - high
then drops again
How do rocks evidence climate change
diff rocks are more prevalent + dominant in different climates e.g. some rocks form from different weathering
some only form in certain climates
what rocks are used to identify climate
Coal
Desert sandstone
Evapourites
Tillites
Reef limestone
all of these rock types are found in UK
what does Coal tell us about past climate
Warm and wet
mostly from Carboniferous in UK
Must be highly productive ecosystem = peat
rapid plant growth + high rainfall and temp e.g. rainforest
what does Desert sandstone tell us about past climate
Hot, arrid and dry
sand exposed to air -> oxidised -> red
fine grained + V well sorted + well rounded
Mostly quartz
transported by wind -> dunes
Occurs 20-30 degrees north or/and south
what does Evapourites tell us about past climate
desert + quick change from wet to dry
form where low rainfall and high evap e.g. hot desert
found at latitudes 20-30 degrees north or/and south
what does Tillites tell us about past climate
Glacial deposits –> cold enviro
ancient boulder clay -> commonly formed at high latitudes
more than 60 degrees north/south of equator
some in low latitudes
what does Reef limestone tell us about past climate
warm and shallow
mainly built of colonial corals
restricted to latitudes < 30 degrees north/south of equator
likely at this latitude
what is palaeontology
the branch concerned with fossilised organisms
How does paleontology evidence climate change
diff organisms based in diff atmospheric conditions
certain species associates with certain climates e.g. corals
based on modern day animals tell what similar past species preferred for climate
corals as evidence of past climate
modern - live in narrow range of temp and depth -> 30degrees N or S of equator - allowing for symbiotic relationship with algae
Palaeozoic tabulate corals have similar O18 : O13 as modern corals = require same tropical conditions
Plants as evidence of past climate
excellent indicators e.g. tree rings, leaf size and shape
lack of tree rings in carboniferous suggest non seasonal equatorial climate = same as modern day
also grew to 40m+ = hot humid equatorial climate and latitude allowing biomass to accum
isotope
atom of an element with the same no of protons but different no of electrons
same chem props (same no of outer shell electrons) diff physical props
isotopes of O as past enviro indicators
O16-99.76% O17-0.04% O18- 0.20%
normal= O16 evaps, falls as precipitate -> returns to ocean
O16 evaps as lower mass so requires less e to evap –> more easily
cold period= glaciers -> O16 trapped in ice -> amount of O18 increases in comparison to O16 in ocean
^ O18:O16 = colder climate
isotopes of C as past enviro indicators
C12- 98.9% C13-1.1%
plants prefer C12 + take up
Warm= more plants -> more C12 taken up + stored, ratio of C13:C12 in ocean increases e.g. 5:95 instead ( if too warm kills plants and opp happens)
Cold= No plants, No C12 stored so ratio of C12 in ocean increases, C13:C12 decreases
ratio preserved in sed then becomes rock
evidence for Northward drift of the British isles in rocks
tillites - Precambrian in west scot = glaciation
colonial corals- in silurian wenlock limestone + jurassic - shallow tropical sea
red sandstone +evapourites - permian + triassic = 30 degrees N of equator
reef limestone- lower carboniferous in Pennines = tropical seas
coal - scot to kent carboniferous = equitorial rainforest delta
Chalk- cretaceous = temperate as moved north into cooler climate - rep modern climate
what is an eon + current
largest unit of geological time
Phanerozoic
The 4 Eons
Hadean, Archean, Proterozoic and phanerozoic
What is an era + current
smaller than eons larger than periods
Cenozoic
The 4 eras
Precambrian, Palaeozoic, Mesozoic and Cenozoic
What is a period + current
smaller than eras larger than epochs
Quaternary
The 11 periods
Cambrian, Silurian, Ordovician, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, tertiary and quaternary
What is a epoch + current
smallest unit of geological time
holocene
Arguments for the Anthropocene epoch
The human impact on Earth (climate and enviro)
Current mass extinction
Arguments against the Anthropocene epoch
only very short time period
geological events occur over long period of time not abruptly
recency bias
not yet accepted by international commission on stratigraphy
5 major extinction events oldest to youngest
Ordovician- Silurian 443ma cooling
late Devonian- 372ma cooling/volc
Permo-triassic- 252ma volc? lava + gases
Triassic-jurassic- 201ma volc eruptions
cretaceous tertiary- 66ma asteroid
Evidence for current mass extinction- driven by human activity
species extinction rate 1000-10000x higher than natural
amphibians greatest rate 25000-40000x background rate
excluding bacteria there are 8.7 million species so at a rate of 50000 a yr we will have none in 174yrs
more reasonable to lose 75% of species in next few centuries
What is a marker horizon
stratigraphic units of same age and distinct composition and appearance
allow to determine age / time period formed in
easily distinguished
What is GSSP
Often referred to as golden spike
Golden standard stratotype - sections + points
locations where strata show evidence on worldwide scale –> set as boundary for time period
Examples of GSSP
iridium from asteroid - Cretaceous tertiary
plutonium-239 (half life = 24000yrs) from nuclear testing e.g. bikini atoll
agriculture - adding N + P as fertiliser
plastic
soot from industrial rev
