Hey everyone, my name is Nancy Merino
and I am a scientist at Lawrence Livermore National Lab.
One of the research areas I think about
is the likely environments for studying origins of life.
In order to do this, we have to first understand
what it might have been like on Early Earth billions of years ago.
Then, once we have an idea of that, we can look around on Earth today
for similar environments and search for life.
The idea is that we can find clues about early life within modern day life -
much like how your own life is a reflection
of your own personal history and family's history.
Life probably started around 4.4 to 3.8 billion years ago.
The origins of life is still a highly debated topic,
so the range still covers billions of years.
This is what's shown here in the timeline of Earth's history,
from its formation about 4.5 billion years ago
to the current times.
There are four different eons of Earth,
known as the Hadean, Archean and Proterozoic and Phanerozoic Eons.
These are all major time periods
marked by drastic changes in the Earth's environment.
It's believed that life originated
some time during the Hadean and Archean Eon.
And, during this time,
there is also probably a lot of comet and meteorite impacts -
and this is what's known as the "Late Heavy Bombardment."
These comets and meteorite impacts
would have influenced the Early Earth environment
because there were just so many of them.
It is one reason why some scientists think
that life may not have started during the Hadean Eon
because it was extremely hot and probably inhospitable for life.
This is an image showing what it might have looked like on Earth
during the Hadean Eon.
But, this is still a highly debated topic
because we don't have a really good rock record.
However, we do know that Early Earth
was probably an extremely hot environment.
There were also magma oceans.
So, instead of water,
the Early Earth oceans were made of magma.
These magma oceans started because of several reasons,
one of which is comet and meteorite impacts,
which heated up the surface of the Earth.
Another is tidal heating, which has influences
from how close the Moon is to the Earth.
Another is core formation, where comet and meteor impacts
will deposit metals onto the surface of the Earth,
and this will begin sinking towards the inner layers of the Earth,
helping to form the Earth's core.
This process is known as "plate tectonics."
So, Earth has a thin surface layer, which is cracked and can move around.
This is the reason for earthquakes, and it is also essentially
the recycling of Earth's surface with the inner parts of the Earth.
This process could have started as early as 3.8 billion years ago
and is definitely occurring around 3.2 billion years ago.
This motion most likely helped make the Early Earth environment
more favorable for life by helping to cool down the Earth.
In addition to influencing the origins of life,
plate tectonics also influenced the evolution of life
through the creation and movement of continents.
A necessary requirement for plate tectonics is water.
Before plate tectonics really got started,
oceans probably started to form during the Hadean Eon.
But, it is not until the Archean Eon
that there are really global oceans covering the surface of the Earth.
This water didn't just come from nowhere
and there were at least three sources of water.
One is from plate tectonics influencing the amount of water on Earth's surface.
Another source is from volcanoes, which were very active at this time
and would have helped the conversion of water vapor into liquid.
The third source is from delivery by comets and asteroids,
which are rich in ice.
Water is definitely one of the most important substances
at this time to help start life
and is really the main criteria for life on Earth.
For example, water plays an important role
in the stability and dynamics of life's major compounds -
like proteins and DNA.
Life took hold on Earth during the Archean Eon.
There were a mix of things going on at this time,
which made it possible.
This includes a not so hot environment,
mainly due to the cooling of Earth by plate tectonics and other processes -
the formation of a global ocean
and the collection of the necessary ingredients on Early Earth
to actually build a cell-like shape.
However, life during the Archean Eon had to survive without oxygen.
The atmosphere probably had nitrogen, carbon dioxide, water
and some amounts of sulfur, methane and ammonia.
The atmosphere during this time is actually still highly debated,
but scientists agree that Early Earth atmosphere
during this time had no free oxygen.
This atmosphere is very much different from today's atmosphere,
which has 21 percent oxygen.
The earliest life-forms were probably what we call "chemolithoautotrophs."
The first part of this word is "chemolitho,"
and that's short for chemolithotroph.
This is Greek for "rock-eater," and it means
that the earliest life-forms probably used inorganic compounds -
for example, iron or sulfur to get energy.
The second part of this word is "autotroph."
This means that the first cells used carbon dioxide for getting carbon.
Carbon is the necessary building material for our cells,
And so, the Archean Eon essentially had all the necessary ingredients for life.
We know that life probably took hold in the Archean Eon
because there is evidence of life in the rock record.
The first likely signs of life in the rock record
starts around 3.5 to 3.3 billion years ago.
Here is an image showing a microfossil from a rock in Western Australia,
which dates back to that time.
Now we have an idea of what Early Earth was like,
in now - in modern times - we are faced with the task
of deciphering the origins and evolution of life.
How can we think about early life right now?
To build on top of that,
how can we think about life on other planetary bodies?
And, modern day Earth actually has some answers for us.
The Earth today is covered with many modern-day analogues
for Early Earth and other planetary bodies.
These are all extreme environments.
This image here shows the locations
where microorganisms have been discovered
all the way from the deep parts of the ocean
to the Arctic and to volcanoes.
All of these environments have some kind of extreme component
that requires microbes to have the necessary adaptations to survive.
So, by studying these environments, it allows scientists to understand
how microbes can adapt to extreme environments
and how they might have lived on Early Earth,
and the potential for life on other planetary bodies.
Many microbes have been identified in these extreme environments,
and the microbes that can survive under extreme conditions
are known as "extremophiles."
Extremes include temperature, pH, salinity, pressure,
desiccation - or extreme dryness - and radiation tolerance.
Here are five microscope images
of microbes that can survive under the most extreme conditions,
and these are the current record holders.
So, for example, Methanopyrus kandleri can grow
at temperatures up to 122 degrees Celsius -
so this is way above boiling water.
But, because of high pressure,
the water where this microbe is naturally found does not boil -
and so, this microbe can survive both high temperatures and high pressure.
And, because it can survive multiple extremes,
it's also known as a "polyextremophile."
Life on Earth could potentially survive under even more extreme conditions.
This image here is showing temperature, pH,
pressure and salinity on different axes.
The temperature ranges from minus 300 to 500 degrees Celsius,
the pH ranges from minus 4 to 14,
the pressure ranges from zero to 1000 megapascals
and salinity ranges from zero to 50 percent.
The minimum and maximum for each parameter
is plotted for life on Earth,
and so we can see the space in which life on Earth occupies.
Now, when we look at all the known extreme environments on Earth,
we can see there is potential
to push the boundaries of life on Earth even further.
For example, the maximum temperature
life can grow at is currently 122 degrees Celsius,
but Earth's environments can reach to much higher temperatures.
It may not be possible for life to survive at 400 degrees [Celsius],
but there is potential for microbes
to survive a bit hotter temperatures than 122 degrees [Celsius].
So, there are many unexplored regions of Earth
where new microbes have yet to be discovered.
But, what about other planetary bodies?
When we look at the environmental conditions
on the planets Mars, Venus and the dwarf planet Ceres,
as well as the icy moons Titan, Enceladus and Europa,
we can see that there are some portions of those planetary bodies
which match up to the environmental conditions on Earth.
So, by studying the modern-day analogues on Earth,
we can further understand life itself and also explore life in the Universe.
So, that ends my lecture on the likely environments for studying origins of life.
Here are three books which are really good reads
for getting into the origins of life in the field of astrobiology.
They all provide really good history and background for this field.
Finally, here are all the references that were used in this lecture.
So, I encourage you to look them up
and thank you so much for listening to my lecture.