>> One of the prime ingredients of life is order as opposed to chaos.
We can see patterns in life.
Ranging from microorganisms to the largest scale creatures on the Earth.
This regulatory is an essential ingredient of biology.
Another essential ingredient is the use of energy.
The fundamental source of energy for all life on Earth is the sun, but
life can involve primary use of that energy through photosynthesis or
secondary or even tertiary use of that energy.
In all cases however,
when it's traced back, the life source is radiant energy from our star.
More generally we can make a list of properties that biological
organisms seems to share.
They all have order, they adapt to their environment, they regulate
their physical conditions, they process energy, they grow and develop.
They reproduce and they respond to their environment in an interactive way.
Are all these ingredients essential?
What are the necessary and sufficient conditions for biology?
We don't know the answer to that question.
Another extraordinary attribute of biology, is its multi-scale nature.
There is a hierarchy of biological organisms.
At the high end, this ranges to an entire ecosystem.
With interrelated parts,
each biologically regulated, we can take that down in scale to a rainforest,
which also has interacting aspects in terms of different organisms.
And then down to the single organisms themselves.
Perhaps, a tree.
Then down in scale to the leaves, or individual components of the tree.
And finally, to the tissue material.
And the different types of cells, each one a chemical factory.
At the base of this are small units within a cell
carrying out discrete biological functions and the individual molecules themselves.
The reductionist approach to biology fails.
The inter-related parts produce emergent behavior at higher scales
that are not predictable from the sub-components.
Astro biologists think there are two essential ingredients for
life, both on earth and elsewhere.
One is water, all life on earth contains water.
Ranging up to 99% for jellyfish down to 30% for bugs and beetles.
We as humans are in the middle of this range with about two-thirds
of our mass water.
Water is a solvent and facilitates chemical reactions.
We think water is essential for life and life formed in water on the earth.
And this will be the case elsewhere as well.
The other essential ingredient is carbon.
Carbon facilitates long complex molecules.
In fact, the toolkit of carbon chemistry, or organic chemistry, is infinite.
These are not special requirements for life beyond Earth, because water is one of
the most abundant molecules, and carbon is one of the most abundant elements.
The context for astrobiology is the nature of biology on this planet.
Even the definition of life is difficult.
For example, we could use a very specific definition
that hones in on the particular attributes of life on Earth, and
that might exclude variants that we might find beyond Earth.
On the other hand, if we used too general a definition, like processing energy and
organizing information.
We might not be able to recognize life.
Terrestrial biology is a multi-scale phenomena that operates
on the size of the planet down to the level of individual molecules.
The interrelationship between these component parts is complex and
not completely predictable.
Chris ImpeyDistinguished Professor
