4.1 - Origin Of Life On Earth

Question 1

Does habitability imply biogenesis?

Answer 1

No habitability does not imply biogenesis.
Habitability refers to the conditions under which a planet or moon has the potential to support life, based on factors such as temperature, atmospheric conditions, availability of water, and others.

Biogenesis refers to the origin of life and the processes by which living organisms arise from non-living matter. A habitable environment does not necessarily mean that life has arisen there or will arise there, but it provides the necessary conditions for it to be possible.

Question 2

Did life originate from a global chemical reactor?

Answer 2

There is much uncertainty about how life originated. The chemical reactor theory is one way scientists believe life originated.

According to this theory, life originated from a self-sustaining chemical reaction that took place in a suitable environment, such as a warm pond, volcanic vents in the ocean, or even meteorites. This reaction resulted in the formation of simple organic molecules that eventually led to the formation of more complex molecules, such as proteins and nucleic acids, which are the building blocks of life.

Question 3

What is LUCA?

Answer 3

The last universal common ancestor, which was likely distinct from the first common ancestor on a dynamic young earth

CHNOPS = life evolved from gases (plus P)

Question 4

What did Louis Pasteur believe in 1862?

Answer 4

That life does not emerge spontaneously from an organic soup.

Specific environmental conditions and planetary processes were necessary for the origin of life

Question 5

Germ hypothesis vs Spontaneous Generation hypothesis

Answer 5

Germ hypothesis = Pre-existing microorganisms present in the air can contaminate the nutrient broth

Spontaneous Generation Hypothesis= Living organisms can be generated spontaneously from non living organisms molecules in broth

1. The flask is sterilised by boiling the broth
2. The unbroken flask remains sterile
3. The broken flask becomes contaminated after exposure to the germ laden air

This results in airborne germs entering the broth which grow

Question 6

Building blocks of life

Answer 6

All life on earth uses the same building blocks, many of them have been synthesised in prebiotic reactions

Question 7

What is the ‘central dogma’ in biology?

Answer 7

The ‘central dogma’ must be a very early invention, dating back to the last universal common ancestor with roots in prebiotic chemistry.

• DNA stores information, the information is transcribed to RNA
• From RNA, the information is translated into proteins

Proteins execute specific functions:
- Replication (making new DNA)
- Metabolism (harnessing energy)
- Motion

All life on earth operates by this scheme

Question 8

What do we know about relatively easy gas phase reactions?

Answer 8

1. Gas phase reactions are typically fast and highly reactive due to high kinetic energy of gas molecules and the ability of gas molecules to collide and react with each other.
2. Gas phase reactions can have significant impacts on the environment, such as the formation of air pollutants and the production of greenhouse gases.

Reduced gases from volcanoes (H2, CH4, NH3, H2) and energy (heat, electric discharge, UV etc)

• While gas phase reactions from volcanoes can produce a variety of atmospheric pollutants, the direct formation of significant amounts of cyanide and formaldehyde is unlikely.

Question 9

What is the foremose reaction?

Answer 9

• Formaldehyde (HCHO) is a volatile and highly reactive organic compound. The Formosa reaction is a chemical reaction where HCHO is converted into a variety of complex organic compounds like sugars, amino acids and nucleotides. The Formosa reaction is thought to be a key step in the prebiotic syntheses of biologically relevant molecules and is therefore of significant interest to the field of origin of life research.

Question 10

What is strecker synthesis?

Answer 10

• Hydrogen cyanide (HCN) is a highly toxic gas. Strecker synthesis involves the conversion of amino acids into alpha-amino nitriles through the reaction of an aldehyde or ketone with HCN. It is important reaction in organic synthesis and is used as a tool to determine the stereochemistry of amino acids.
• Formaldehyde can be used as the aldehyde in the strecker synthesis reaction. HCHO will react with hydrogen cyanide (HCN) to form an alpha-amino nitrile and water

Question 11

Reactions in the lab that produce water-soluble products?

Answer 11

• HCHO to simple sugars through the Formosa reaction
• HCN and HCHO to alpha-amino acids in the strecker reaction

Question 12

Reactions in the lab that produce water-insoluble products?

Answer 12

C02, H2 and heat with an iron catalyst turns to hydrocarbons and amphiphiles (lipids, long chain fatty acids and alcohols) through the Fischer-tropsch type reactions

Question 13

What reactions are not well understood?

Answer 13

Polymerisation reactions (making chains).
We know how to synthesise many of the organic compounds required by life, but we know little about how to incorporate these into useful macromolecules

• Amino acids + dry heat to form protein like chains as proto-enzymes
• Nucleobases, sugar and phosphate to form nucleic acids, DNA, and RNA

Polymerisation often requires dewatering (removal of OH groups) and so is possible favoured in evaporitic environments. Clay mineral may have acted as templates.

Question 14

What is the lightning discharge reaction?

Answer 14

It is also known as strecker synthesis

• The reaction is promoted by acid. HCOH and HCN must be supplied or generated
• It requires energy input, such as lightening discharge in the atmosphere or heat from hydrothermal vents
  (Miller and Urey, 1959)

Question 15

What is the Formose reaction (Aleksandr Butlerov, 1891?)

Answer 15

• The formation of sugars from formaldehyde by condensation (eg. Evaporation)
• The reaction is catalysed by a base (requires a high pH) and by divalent metals (eg. Ca2+)
• It is favoured in the presence of borate evaporite minerals

Question 16

What is the Fischer-tropsch type reaction?

Answer 16

• Originally developed to produce fuel (C-C chains) from inorganic precursors
• C02 and C0 are reduced to CH4, and long-chain hydrocarbons by reaction with H2 at 200-250 degrees and high pressure. It requires a metallic mineral as a catalyst
• Geological sources of C02 (CO) and H2 are volcanism and serpentinisation

Question 17

Where did life originate?

Answer 17

There are numerous settings and reaction mechanisms that have been proposed for the formation of specific building blocks.

The first living cell (self-replicating and metabolising) must have already have been highly complex, composed of diverse macromolecules.

• No single environment can fulfill all of these requirements and so was environmental complexity a necessary condition?

Question 18

Were different settings involved in the origin of life?

Answer 18

Multiple different settings were involved in the origin of life by continuously exchanging reactants and products (LGT and rapid evolution of viruses are high-tech examples of physical information exchange in modern life)

• Each setting natured a subset of reactions, favouring certain compounds while destroying others (natural selection on a molecular level)
• Over time, building blocks were slowly assembled in one type of setting, perhaps trapped in a biofilm, or within mobile photocells

Question 19

What reactions had major advantages in each setting?

Answer 19

Reactions that were most relevant and dominant within each setting were also the most productive

Question 20

Geochemical cycles evolving into biogeochemical cycles

Answer 20

The transition from geochemical cycles to biogeochemical cycles refers to the inter gratin of biological processes into earths chemical cycle.
In a geochemical cycle, the movement of elements and minerals through ther earths systems (eg. Atmosphere) occurs through non-biological processes such as weathering, erosion, and volcanic activity.

In a biogeochemical cycle, living organisms,s play a key role in the cycling of elements and minerals, incorporating them into their tissues and altering the chemical composition of their environment through metabolic processes.

The integration of biology and geochemistry leads to a more complex and interrelated set of processes that drives the earths natural systems.

Question 21

What may have emerged as the chemically fittest product of a global reaction network?

Answer 21

Life and biochemical unity

Question 22

How may metabolic and genetic diversity evolved rapidly?

Answer 22

They could have evolved rapidly if they were inherent to prebiotic chemistry

Question 23

What might planets that lack environmental diversity not have?

Answer 23

Might not have the capacity for a de novo origin of life, irrespective of their volatile inventory

Question 24

What is an inescapable reality for origin of life models on earth?

Answer 24

The environmental complexity and mixing of processes

Question 25

What are sea ice brine pockets?

Answer 25

They are concentrations of organics and mineral grains in brine pockets

• Low temperatures stabilises reaction products
• Gradients in salinity, pH, light and temperature
• There is no geological evidence for or against ice, but consist with the faint young sun paradox

Question 26

What is the sea surface micro layer?

Answer 26

It is an interface between the atmosphere and the ocean where there is solar radiation and oil slick accumulation

• Adsorption to suspended particles, in particular buoyant grains of pumice with catalytic properties
• decanoic acid is shown to spontaneously form flocs (salt water) and vesicles (freshwater or with adenine)
• there are lipid coatings on pumice acting as a ‘biofilm’

Question 27

What is important about meteorite dust?

Answer 27

It acts as a source of highly soluble and reactive phosphorous compounds or organic precursors

Question 28

What is the significance of hydrothermal vents?

Answer 28

• They are concentrating mechanisms of organics in porous vent structures
• They provide abundant metals, H2 and C02 as sources of energy and fixed carbon
• They are abundant in zeolites, pyrite, carbonate and clays
• They create gradients in temperature, pH and salinity

Question 29

Impacts of hydrothermal systems that are Temp driven and magma hosted

Answer 29

1. Acidification
2. Metal enrichment (from sulphides/oxides/silicates)

Question 30

Hydrothermal systems that are serpentinization driven

Answer 30

Occurs when seawater makes contact with ultramafic rock, generating hydrogen that can reduce carbon dioxide to methane geochemically.

H+ consumption and generation

• occurs at mid ocean ridges