L9 - Life and the Atmosphere

What is life?

• ‘Life is a sustaining chemical system capable of Darwinian evolution’ - NASA 2021

• Darwinian evolution relies on natural selection: organisms that produce offspring that have heritable variation that gives rise to competitive advantage for a limited resource.

What 4 compounds are all life forms reliant on?

• Carbohydrates - all life forms use to store energy

• Lipids - all life forms use to store energy

• Amino acids - produce proteins: all life forms use ‘left-handed’ amino acids

• Nucleic acids - RNA (more primitive version of DNA), DNA, etc.

Where did life originate on the planet? Why?

• Water is very good at absorbing Ultraviolet Light - UV light breaks up organic molecules.

• Life is unlikely to have been formed on the terrestrial surface of the planet because it would have been subjected to UV.

• Life must have formed in water, which protects it from UV light

What was discovered in Miller’s experiments?

• In this simple organic experiment, they were able to produce amino acids and, later, nucleic acids. And they were able to do this abioeically.

• You could produce the molecules necessary for life, without life

• These molecules have also been found on asteroids: possible that the first organic compounds present on the Earth came from space.

How do black smokers work?

• Occur when the oceanic crust is thin, near oceanic ridges, and where the asthenosphere is relatively close to the surface.

• The oceanic crust cracks, cold water seeps through, is heated up, and flows upwards due to low density.

How do black smokers and hydrothermal vents provide evidence for life formation?

• As the water reacts with the oceanic crust, it loses sodium and magnesium that is removed from the water.

• The minerals in the ocean crust (pyroxene, plagioclase, olivine) react to from sheet silicates to release iron, manganese, copper, lead, etc.

• The metals acts as catalysts, lowering the activation energy, making it easier for things to from.

• The metal-enriched water flows out of the cracks and the metals precipitate with sulphide ions to create metal sulphides.

How can the influence of black smokers be traced?

• ³H is released through black smokers.

• These plumes of ³H can be tracked for thousands of kilometres.

• The seawater percolates through the crust, sodium, and magnesium is removed from the seawater, and other elements are released (strontium)

• It is possible that life originated from black smokers.

What is polarity?

• A cell membrane collects and protects these molecules, and it is thought that cell membranes are formed through abiotic processes.

• This depends on a property called polarity

What is a water dipole?

• Water molecules have polarity

• Oxygen is slightly negatively charged and the hydrogen is slightly positively charged

• The molecule has a zero change.

What is a hydrated cation?

• Positively charged atom that dissolves in water

• Positively charged ions can dissolve in water because the water molecules cluster around them

What is a hydrated anion?

• Negatively charged ion

• The hydrogen atoms in the water are attracted towards it.

• Negatively charged ions dissolve in water because water molecules cluster around them.

What does polarity explain?

• Polarity explains why organic molecules do not dissolve in water

• Polar molecules (e.g. water molecules) are attracted to the opposite charges.

• Non polar molecules do not have charges so water does not cluster around; the non polar molecules are shunted over to one side

  • They do not mix

What is self-organisation and why does it happen?

• Polarity gives rise to self-organisation: a natural property where some structure appears driven by thermodynamics

How could self-organisation have given rise to cellular membranes?

• If fatty acids are together, they line up according to polarity: polar molecules clump together and nonpoalar clump together.

• Once this layer is formed, it will flip over on itself to produce a double layer

• They then form spheres: if water and fatty acids are combined, water will be trapped by the spheres.

• So, a cellular membrane can be formed where water is in its centre with dissolved organic compounds which can protect those organic molecules

Therefore, cellular membranes may have originated as self-organising phenomena which can be produced abiotically.

Why is RNA thought to be a form of primitive life?

• Primitive life (prokaryotes) are a source of heritable material

• RNA, a nucleic acid, can form by inorganic processes and can self replicate.

• RNA can produce proteins; thought to be initial heritable material of life, but then somehow began to form DNA, which became the heritable material as well as producing proteins.

RNA World = hypothesis that life started using RNA rather than DNA as its heritable material.

Why could clay minerals be considered initial life forms?

• If there is a clay material, it is capable of growing and breaking up (having offspring).

• These individual fragments may be different to each other, therefore have variation.

• Once these fragments start to grow, they might preserve this variation - so that it is heritable variability.

• Fragments of minerals with different structures can be more or less favourable to their growth.

• These clay ‘offspring’ can be viewed as having heritable variation - which could affect their fitness for survival

Is life inevitable?

• Thermodynamics suggests it is.

• The 2nd Law of Thermodynamics suggests that energy cannot be created or destroyed, only transferred.

• Whenever a reaction occurs, some of the energy is converted into entropy (unusable energy).

• Life is very good at converting energy to unusable forms of energy and accelerating the development of entropy.

• Ultimately, the universe will eventually die because all of the energy would have been converted to entropy.

What happens if an atom (A) loses an electron to another atom (B)?

• Atom A loses an electron and B has gained an electron

• A has been oxidised (oxidation = loss)

• B has been reduced (reduction = gain)

How is energy converted into ATP?

• If you burn sugar in the presence of oxygen, it is an incredibly efficient way of converting energy into ATP

What is the significance of energy being converted to ATP?

• Thought to be significant step in the evolutionary process because suddenly a lot more energy became available to organisms (used to reproduce and colonise planet)

• This would only happen once levels of oxygen had built up, after billions of years, oxygen would have accumulated in the atmosphere and be utilised by life.

• Left with an oxidised surface layer (Earth’s crust and atmosphere = oxygen rich).

• In the mantle, it is still very reduced but has lots of Fe2+ - sets a massive energy potential because of the reduced phase in the mantle and oxidised mantle on the crust.