Origins of Life

What is abiogenesis?

The theory that living cells arose from non-living matter.

What are the four key stages theorised in abiogenesis?

There was non-living synthesis of simple organic molecules (from primordial inorganic molecules)

These simple organic molecules became assembled into more complex polymers

Certain polymers formed the capacity to self-replicate (enabling inheritance)

These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)

What did the Miller-Urey experiment demonstrate?

That simple organic molecules can be synthesised non-biologically under simulated prebiotic conditions.

What did the Miller-Urey experiment attempt to recreate?

The postulated conditions of pre-biotic Earth using a closed system of flasks and tubes

How did the Miller-Urey experiment attempt to recreate the postulated conditions of pre-biotic Earth

Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions

The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)

This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)

The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week

After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules

What conditions were required for the chemical processes leading to the first life?

A reducing atmosphere and high temperatures (>100°C) or electrical discharges.

Why were high temperatures or electrical discharges important for creating specific conditions for the formation of biological life

They provided energy to catalyse chemical reactions.

What is a reducing atmosphere?

A reducing atmosphere is an atmosphere with little or no oxygen, allowing organic molecules to form more readily.

What is biogenesis?

Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)

What did Louis Pasteur demonstrate that led to the law of biogenesis?

He demonstrated that bacterial growth in nutrient broth was caused by contamination from pre-existing cells, rather than spontaneous generation.

How did Pasteur's swan-neck flask experiment demonstrate biogenesis?

Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass

The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation)

Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside

From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur