How Did Those First Organic Molecules Get to Earth?

How did life start? You would be talking to a Nobel prize winner if I could tell you that. Unfortunately nobody knows. There are a few theories around and a few advances have been made in this field but I will talk about the one that is most widely accepted in scientific circles.

The starting point is way out there in the universe around red giant stars. These are old stars that have used up a lot of their hydrogen and have collapsed to a point where the actual shell of the star burns the remaining hydrogen. The extra pressure due to this burning results in the star increasing in size hundreds of times bigger than our sun.

Red giants are carbon rich which, as most life on Earth is made up of carbon, is a good starting point for the molecules needed. These molecules are similar to the ones found in a candle flame on Earth mostly consisting of aromatic hydrocarbons. The evidence for this comes from the comparison of starlight to planetary hydrocarbons.

Red Giant

The carbon atoms around red giants are blown away by the stellar wind. This is the same sort of thing as the solar wind from the Sun caused by radiation pressure and temperature of the star. The molecules that are blown away from the star reach interstellar space and are then caught in environments that can create matter.

Molecular clouds have a key role in Galaxy evolution as they are the coldest and densest parts of the interstellar medium. Other clouds of dust do not allow the formation of stars because they are less dense and too warm. Planet and star formation in the these clouds is essential for life as we know it due to the formation of planets and the stars but also to produce different molecules. The Orion nebula is an example of a molecular cloud where the process of star formation is occurring.

Orion Nebula

Different types of molecules are produced in the molecular cloud due to their very low temperatures where the organic gases hit dust grains and freezeout. Eventually an icy interior is formed and ultraviolet and cosmic rays processed the particles further. There are certain areas of the molecular cloud where the temperature is warmer and the gas is more dense and these may produce even more reactions in the particles.

It is thought that star formation nearby evaporated the ice on the particles allowing the molecules to return to a gas. In this molecular cloud solar systems are starting to form and inherit the organic molecules from the molecular cloud.

So how did the organic molecules get from the molecular cloud to Earth? Well, nobody really knows but organic molecules have been found in a meteorite called Murchison so it would be a good assumption that organic molecules were brought to the Earth by meteorites. Today meteorites hitting the Earth are regular but not enough to deliver the organic molecules for life. There was a period in the early days of the solar system called the heavy bombardment when there was a large amount of meteorites and this could have spread organic matter throughout the solar system including Earth.

Heavy Bombardment

Panspermia was a proposal brought up a long time ago but has recently surfaced and is becoming accepted by scientists. This theory has the idea that spores in the upper atmosphere of a life rich planet were forced into space by radiation pressure from a star nearby. These spores travelled through space and fell on a different planet (Earth). Panspermia in this form doesn’t really hold much sway with anyone as the spores would be killed by interstellar radiation before they reached their target planet. The spores nowadays are thought to have been carried in the comet and so survived the radiation.

These theories don’t explain how complex lifeforms or even how the first cell formed but to get organic matter to Earth is a start.