Life in the Universe
Contents
Life in the Universe#
Life in the Universe#
What is Life?#
Life is defined by NASA as a system described as
Chemical Darwinian: a self-sustained chemical system capable of undergoing Darwinian evolution.
Darwinian: a system cpaable of evolution by natural selection.
Environment for Life#
Requirement for Life#
The requirments for life can be partitioned into 3 categories:
Supplies
HCNOPS + trace elements
The most significant is carbon which has an enormous variety of roles in life due to the numbers of bonds it can form
Energy
Sunlight
Geothermal
Environment
Water (popular theory of primordial soup)
Stable climate for a long timescale
These requirements are the properties of the planet and star.
Goldilock Zones#
Planetary Habitable Zone#
Galactic Zone#
From our world, life can only exist due to non-deadly conditions and complex chemicals forming our organic materials. This suggest the prime location in the galaxy for life to form:
Life must live further from the galactic center due to frequent supernovae and gamma ray burst (high radiation zones)
Life must not live on the edge of the galaxy due to rare amounts of complex chemicals.
Creation of Life#
Primordial Soup#
The theory first suggested by Charles Darwin that life formed in a small lake with all of the ingredients with life especially when it reacted with the envionrment.
Miller-Urey’s Experiment#
The famous Miller’s experiment succeded in creating amino acid out of a model of the primordial soup. The experiment was set up as so:
Water containing at least HCNO at the lower level to represent the primordial soup.
Air containing at least CNO at the upper level to represent the Earth’s atmosphere.
A spark created from an exposed electrical wire to represent lightning.
All of these three conditions resulted in the creation of amino acid in the primordial soup indicating the possbility of life being created by Earth’s environment (a non-living environment).
Panspermia#
The theory suggest not only the ingredients of life but life (e.g., microbes) itself existed in objects (e.g., asteroids) that would eventually land on a suitable environment (e.g., planets) and start life. This theory also implies the possibility of life on other planets if Earth was a process of panspermia.
Formation of Oxygen Atmosphere#
Oxygen are theorized to be formed majorly by living things around 2-3 Gyr through photosynthesis. It is crucial to prove that life can live without oxygen.
Development of Life#
We’ll now dwell on the theory from the Miller-Urey experiment such that life began with a non-equilibrium impact. We may crudely summarize the formation of life in these steps:
Life originates
First should be RNA (not DNA due to DNA being too twice as complex as RNA).
Cellular formation where organic molecules live in these lipid membranes
Eurkaryotes and prokaryotes
Evolution of eukaryotes to bodied life
Evidence of Very Early Life#
Banded Iron Formation and Cyanobacteria#
We’ll go all the way back 3.85 Gyr which is the age of the oldest sedimentary rocks discovered. The sedimentary rocks have banded iron formation (BIF) that has two colors red (iron-rich) and gray (iron-poor).
These feature are probably caused by cyanobacteria (found in the rocks as microfossils) at near-surface waters that interact with \(\rm{O_2}\) and bond with \(\rm{Fe}\) forming iron-oxides \(\rm{FeO}\) that gets deposited in the rocks in a periodic way alternating bands.
The variation of the colored bands are probably due to fluctuation of \(\rm{O_2}\) content in the atmosphere.
Oxygen was not present in the Earth’s atmosphere until 2-3 Gyr ago.
The cyanobacteria seems to be able to live without oxygen since they exist in the 3.2-3.5 Gyr bands of the rocks.
Stromatolites#
The stromatolites are structures aged at most 3.8 Gyr at near-surface water which are built by microscopic eukaryotes.
The eukaryotes seems to also live without oxygen.
Extinctions and Impacts of Life#
Extinctions and impacts are the great dangers of life with the possibility of wiping all of life. I will consider extinction as a part of the impacts.
Life cannot have lived too early in the Earth’s age due to a very high rate and large impact (asteroid fields size of planetesimals)
The current line of life should have survived all of the impacts so far due to the diminishing power of impacts or the stability of Earth’s system.
Earths’ system evidence of stability is the requirement that it needed 4 Gyr of stable water to create life as the Sun undergoes its Young Faint Star phase.
The survival of impacts must mean that extremophiles exists.
Extraterrestial Life#
Fermi Paradox#
The Fermi paradox answers the question:
If the universe is so vast, where is everyone else?
The Fermi paradox is an argument of timescale with the main argument
The lifetime of a civilization is much shorter than the time it takes to develop the intergalactic technology and the time it takes for information to reach another civilization (limit is the speed of light).
The hubris of civilization is that they will eventually destroy themselves while attempting to advance to save themselves.