Lecture 4 Flashcards by Madelynn Hamilton

What does the precambrian account for?

Most of the Earth’s total history

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When was there first evidence of liquid water on the Earth? What is the evidence from?

3.4 Ga
Evidence from zircon

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When was there first emergence of life?

3.6 Ga

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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

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Paleotemperature: Precambrian oceans

Silicon isotopes in cherts suggest that the average seawater temperature cooled from 70degC (mid-Precambrian) to 20degC Proterozoic (late Precambrian)

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How did life emerge on Earth?

DNA is required to store genetic info
All forms of life rely on a similar genetic code

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What chemical elements are necessary for life to develop?

CHNOPS

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2 main hypotheses for the origin of life

From ET source/equipped with similar genetic code
From chemical precursors/abiogenesis

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What is the hypothesis that life came from extraterrestrial source/equipped with similar genetic code?

Panspermia

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What 3 sub-hypotheses are there for the hypothesis from chemical precursors/abiogenesis?

Primordial soup hypothesis (Oparin-Haldane)
Hydrothermal vents
RNA World hypothesis

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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

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Who came up with Panspermia?

Richter, Kelvin, and Arrhenius

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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

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Primordial soup hypothesis developers

Oparin-Haldane

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Primordial soup hypothesis

Organic compounds developed from inorganic molecules

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What kind of atmosphere was present for the primordial soup hypothesis?

Chemically reducing atmosphere

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What was in the primitive atmosphere according to Oparin-Haldane?

CH4
H2O
NH3
CO2
H2S

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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

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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