Lecture 4 Flashcards
What does the precambrian account for?
Most of the Earth’s total history
When was there first evidence of liquid water on the Earth? What is the evidence from?
3.4 Ga
Evidence from zircon
When was there first emergence of life?
3.6 Ga
How was the planet Earth billions of years ago?
Atmosphere and ocean virtually devoid of oxygen
High UV radiation, lightning, volcanic activity, frequent asteroid collisions
Paleotemperature: Precambrian oceans
Silicon isotopes in cherts suggest that the average seawater temperature cooled from 70degC (mid-Precambrian) to 20degC Proterozoic (late Precambrian)
How did life emerge on Earth?
DNA is required to store genetic info
All forms of life rely on a similar genetic code
What chemical elements are necessary for life to develop?
CHNOPS
2 main hypotheses for the origin of life
From ET source/equipped with similar genetic code
From chemical precursors/abiogenesis
What is the hypothesis that life came from extraterrestrial source/equipped with similar genetic code?
Panspermia
What 3 sub-hypotheses are there for the hypothesis from chemical precursors/abiogenesis?
Primordial soup hypothesis (Oparin-Haldane)
Hydrothermal vents
RNA World hypothesis
Are the main hypotheses for the origin of life chemical, biological, or paleontological? Why?
They are chemical and biological, not paleontological
The earliest life is VERY unlikely to have left any fossil record
Who came up with Panspermia?
Richter, Kelvin, and Arrhenius
Idea behind Panspermia
Life came from outside the biosphere, possibly carried by space bodies [meteorites, comets or asteroids]
Idea that life occurs throughout the universe
Primordial soup hypothesis developers
Oparin-Haldane
Primordial soup hypothesis
Organic compounds developed from inorganic molecules
What kind of atmosphere was present for the primordial soup hypothesis?
Chemically reducing atmosphere
What was in the primitive atmosphere according to Oparin-Haldane?
CH4
H2O
NH3
CO2
H2S
Explain in more depth the primordial soup hypothesis?
The simple molecules of primitive atmosphere were broken into free radicals
Monomers accumulated in the “primordial soup”
Transformation into more complex organic polymers –> living molecules, cells
Experimental work on the primordial soup hypothesis
What was the name of the equipment used?
In vitro verification by Urey and Miller
Urey-Miller Apparatus
Sources of energy for the primordial soup hypothesis
Electrical shocks (lightning)
Thermal shocks (volcanism)
UV, solar winds, X-rays, Gamma rays
What was in the primitive ocean in the primordial soup hypothesis?
Low concentrations of aldehydes, carboxylic acid and simple AAs
What is a prokaryote?
Single-celled organism
No membrane-bound nucleus or organelles
Asexual reproduction
Heterotrophs
Organic food source
Autotrophs
Inorganic food source
Mixotrophs
Inorganic + organic sources of carbon
Phototrophs
Light as energy source
Chemotrophs
Oxidation of organic or inorganic compounds as energy source
Bacteria/cyanobacteria
Cosmopolitan (virtually everywhere on Earth)
Chemotrophs, heterotrophs or phototrophs
Archaea
Cosmopolitan
Lot of them are extremophiles: thrive in extreme conditions (T, salinity, pH, oxygen availability)
Resistant to UV radiation
How do they differ from one another? (Bacteria/cyanobacteria, archaea)
Different cell wall composition
Archaea have more complex RNA
Different metabolic pathways
When did the Great Oxidation Event occur?
2.45-2.32 Ga
What was the key thing that happened in the great oxidation event?
Emergence of an aerobic earth system
Evidence for great oxidation event
Banded iron formation
Free oxygen for iron to precipitate
Other indications for constraining timing of GOE
Rusty red soils on land
Disappearance of easily oxidized minerals such as pyrite from ancient stream beds
Evidence from S isotope record
Significance of stromatolites
First organic structures
Identifiable aspect of stromatolites
Characteristic banded pattern
How are stromatolites produced?
By the precipitation of carbonate and/or trapping of sediment in relation to the metabolic activity of cyanobacteria (bacteria with photosynthesis)
In what environments are stromatolites produced?
Shallow aquatic environments; marine (sea) or lacustrine (lake)
Explain the accretion process of stromatolite
Mats of cyanobacteria; produce a sticky of mucus; photosynthetic activity –> precipitation CaCO3
Sediment particles get trapped in mucus
A new layer of cyanobacteria grows on top; structure is cemented through precipitation of CaCO3
What kinds of structures create stromatolites?
Multi-layered structures produced by activity of ancient cyanobacteria
Can be considered as fossils or as sedimentary structures
Date of oldest found stromatolite
3.6 Ga
Where are stromatolites found in NB?
Green Head near SJ (Stonehammer Geopark)
Hopewell Cape
Modern stomatolites
Rare and genera
Used as analogue for ancient stromatolites
Occurrences of modern stromatolites
Shark Bay, Australia
When was the acme of stromatolites?
Proterozoic
Paleozoic and Mesozoic stromatolites
In the Phanerozoic, stromatolites are much rarer because microbial mats get grazed by snails and other animals
Stromatolites bounced back and took over after mass extinction events
