Australian Space Science Conference 2011
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Charles Lineweaver

What can life on Earth tell us about life in universe?

Charles Lineweaver
Planetary Science Institute, Australian National University

Aditya Chopra
Planetary Science Institute, Australian National University

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     Last modified: July 31, 2011

Abstract
The universe is filled with stars similar to our Sun, rocky planets similar to our Earth, water like our oceans, amino acids like our proteins and all the other ingredients for life. But is the universe filled with life? If it is, what kind of life is it? We argue that if there is life out there at all, its basic features are likely to be a subset of the features common to all terrestrial life.
We review the most fundamental features common to all terrestrial life and discuss why some of them are likely to be universal while others, although ubiquitous in terrestrial life, should not be expected to be features of extraterrestrial life (ET).

Our predictions for universal features consider mechanisms for planetary formation and the origin of life that should be common in the universe. These mechanisms constrain the abundances of different molecules and elements that are likely on a habitable planet and it becomes possible to predict the composition and biochemistry of ET. Principles of thermodynamics and Darwinian evolution impart directionality to the evolution of life and we discuss features that result from such directionality.

A number of frequently espoused candidates for universal features for life are based on subjective notions of universal fitness, not on features common to all terrestrial life. These features should not be expected to be shared by ET. For example, major transitions in the evolutionary pathway that led to Homo sapiens (such as the origin of intelligence) are sometimes considered to be fundamental transitions in the evolution of all life. However, these “major transitions” are largely arbitrary because a series of different major transitions can be identified along the evolutionary pathway to any extant species.

We suggest that it is more useful to study the shortest branches from the root of the tree of life and identify trends in evolution, often in response to changing environments. For example, we should expect that life on other worlds will also have hyperthermophilic roots.

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