Astrobiology and the Origins of Life
To begin Dr. Awramik's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.
Astrobiology is a new field that discusses the origins,
the distribution and the future of life in the universe. Two
breakthroughs of importance to astrobiology are evidence for the
possibility of the existence of life in the past on Mars and the
discovery of planets around nearby stars. Speculation and early
experiments on the origins of life from Charles Darwin,
Alexander Oparin, H.B.S. Haldane contributed to
a breakthrough experiment by Stanley Miller. Miller took
non-living material that was on the early Earth--hydrogen,
methane, ammonia, and water--provided an energy source and
produced amino acids. In the 44 years since Miller's
experiment, scientists such as Juan Oró and Tom Cech
have produced nucleic acid bases and riboenzymes but no self-replicating
life or organism or cell has yet been produced in the laboratory.
What do we know about the timeline for origins of life on Earth?
Earth formed from the accretion of planetesimals about 4.6
billion years ago. Current estimates are that it took 200
million years, or to about 4.4 billion years ago, until the Earth
had a solid crust, had water and was a habitable environment
for life. The oldest rocks are now placed at about 3.96
billion years and the oldest fossils are from 3.5 billion
years. Four hundred million years of geological record are missing.
This could be the origin of life window.
The oldest fossils are about 3.5 billion years; however, in rocks
dated 3.8 billion years, analyses of isotopes of carbon suggest
that carbon fixation and maybe even photosynthesis
was around then. So now we have evidence of life at 3.8 billion
years ago, some rocks at 3.96 billion and habitability maybe as
far back as 4.4 billion. Think of the primitive Earth crust--
heat, volcanic activity, radioactivity, energy from impacts
of asteroids and comets, water-- as just one big chemical
The fossils from 3.5 billion years are thought to be the remains
of Cyanobacteria. Microbiologists and molecular biologists
have concluded that Cyanobacteria were one of the last major groups
of bacteria to evolve. That would suggest that much of the microbial
evolution at the phylum or division level may have already been
around by 3.5 billion years. If 3.8 billion years is the date
of the last common ancestor that leaves 300 million years
for life to evolve to the level of Cyanobacteria. Microbiologists,
however, believe 300 million years is too short a period of time
for that level of evolution to have occurred.
So where does that put the origin of life? Let's go back
to that exciting breakthrough mentioned at the start of this talk--the
alleged microfossils found in the Martian meteorite in
Antarctica dated 3.6 billion years. The fossil tubular structures
are on the order of 40 or 50 nanometers in diameter. Based on
our understanding of genetic systems on Earth, we're not
sure if a cell that small could contain enough genetic material
We are left with questions and the understanding that there is
a need for a cosmological perspective when exploring the origins
of life. This brings us to the new field of astrobiology.