Download The Future of Life on Earth Over the Next Few Billion Years

The Future of Life on Earth Over
the Next Few Billion Years
Jack O'Malley-James
The Future of Life on Earth Over
the Next Few Billion Years
Jack O'Malley-James
Two main questions
Why are astrobiologists
interested in the future of life on
Earth?
What happens to Earth as it
ages and what does this mean
for life on Earth?
Astrobiology
The search for life beyond
Earth
How do we search for life?
Reflectance from
vegetation
Ozone and Oxygen (together)
Gases in the atmosphere
produced by living things
Ammonia
Liquid water
Methane
How do we find these planets?
Small dips and little wobbles
How do we find these planets?
Small dips and little wobbles
How do we find the biosignatures?
Need a new generation of
space telescopes
Look at star light passing
through a planet's
atmosphere
Molecules in the atmosphere
absorb specific wavelengths
of light
Why look into Earth's future?
Nearly 1000 confirmed planets
outside the solar system
12 considered potentially
habitable
We will eventually find planets that
are like the Earth, but much older
The habitable lifetime of Earth & Earth-like planets
Time (Billions of Years)
Hydrogen converted into helium – heavier
Changes balance of outward pressure and gravity
Results in increasing brightness
Increasing luminosity
Temperatures on Earth increase...
Outgoing
radiation
Reflection
Inc
re
as
ing
...
0 – 0.06
CO2, H2O, ...
Back
radiation
Heat
trapping by
greenhouse
gases
Absorbed by
surface
Re-radiated
from surface
Incoming Solar
Radiation
Weathering
Higher temperatures
More evaporation
More clouds
More rain
Washes out CO2 from the atmosphere via chemical reactions with
silicate rocks
CO2 is crucial for photosynthesis
Less suitable environment for plants
Lightning
Nitrogen + Oxygen
lightning
Nitric acid
Frequency of lightning strikes increases with increasing temperature
Speeds up Oxygen removal from atmosphere
Plate tectonics: Supercontinent cycles
Supercontinent cycles of 100 million-year time scales
Next supercontinent due in ~250 Million years
Can lead to expansive, arid interiors
Plate tectonics: Cooling core
The core is cooling over time
Over billion-year time scales this slows plate movement
Slows recycling of CO2 from the crust to the atmosphere
What does this mean for life on Earth?
Fall in CO2 levels leads to harsher conditions for plants
1 Billion Years
280ppm
CO2
Removes sources of food and oxygen
Results in animal extinctions
1ppm CO2
What does this mean for life on Earth?
La
rge
m
am
m
als
to
i
nv
e
rte
bra
t
Humans?
es
The last animals on Earth
Animals like termites can digest
dead wood and plant matter
Riftia – symbiotic worms that
live near hydrothermal vents
use chemical energy from the
vents for food
Leaves behind a microbial world
Water bears –
microscopic animals that
can survive a variety of
extreme conditions, even
exposure to space
A future world of microbes
Salt
Hot springs, Yellowstone
High, dry and low oxygen
Deep sea vents (hot, high pressure, dark)
Runaway ocean evaporation
Hydrogen loss from upper
atmosphere
After average temperatures
reach a critical point (55ºC)
water vapour enters upper
atmosphere
Ocean evaporation begins
1 billion years from now
Mapping the fate of Earth's final life
Mapping the fate of Earth's final life
Latitude
Mapping the fate of Earth's final life
375
Temperature (°C)
275
“Runaway greenhouse”
175
“Moist greenhouse”
75
Upper
temperature
limit for life
15
Time from present (Billion years)
Conditions no longer suitable for life 1.2 billion years from now at
the equator and 1.85 billion years from now at the poles.
Following the water to refuges for Earth's last life
High altitude pools
Temperature decreases
with altitude
Liquid water could last
longer at higher altitudes
Life could survive for 400
million years longer
than at the surface
Following the water to refuges for Earth's last life
Could losing the Moon prolong the survival of life?
The Moon is receding by 4 cm
a year
In 1 billion years it will pass a
critical distance at which the
Earth's obliquity is allowed to
vary chaotically
Following the water to refuges for Earth's last life
Cold-trap caves (ice caves)
Less dense, warm air cannot enter
Water source
Denser, cooler air trapped
In winter
ICE
Heat from surrounding rock
Cold trap caves on a planet with a largely varying tilt could support
life for nearly 1 billion years longer than at the surface – 2.8
billion years from today.
Following the water to refuges for Earth's last life
Other refuges: (1) Underground
Temperature generally decreases
with depth
Depends on type of rock, which
varies
Parts of the crust could remain habitable for much longer than other
refuges
Following the water to refuges for Earth's last life
Other refuges: (2) In the air
Microbes are already found in
the atmosphere
Highest life found at 77 km
If life could live and grow in the
atmosphere this could be its
final refuge
How do we detect life on a dying planet?
Recently found twin to the
Sun
8 billion years old
If we found a planet just like
Earth, but 3 billion years
older, orbiting this star, would
we be able to tell if there is
any life on this planet?
How do we detect life on a dying planet?
Number of
microbes
that
can live in a
final refuge
+
Rate at
which they
produce
gases
=
Flux of
gases to the
atmosphere
+
Some
atmospheric
chemistry
=
Biosignature
gases
How do we detect life on a dying planet?
How many microbes could live on the farfuture Earth?
In soils, subsurface and sea-floor:
8x1029 cells = 800000000000000000000000000000 cells
How do we detect life on a dying planet?
How many microbes could live on the farfuture Earth?
Time from present (Billion years)
How do we detect life on a dying planet?
How many microbes could live on the farfuture Earth?
Those that need oxygen
will be low in numbers
and disappear faster
Best candidates:
chemolithotrophs
= chemical rock eaters
Alto Ribeira State and Tourist Park (PETAR) , São Paulo, Brazil
How do we detect life on a dying planet?
How many microbes could live on the farfuture Earth?
Chemolithotrophs carry out lots of
different chemical reactions to
make energy
Products such as methane,
ammonia and carbon dioxide
Reach the atmosphere...
How do we detect life on a dying planet?
How many microbes could live on the farfuture Earth?
1.0 billion years: O2, O3, H2O, C2H6 (ethane), NH3, CH4
2.0 billion years: H2O, CH4
2.8 billion years: CH4
How do we detect life on a dying planet?
Back to our dying Earth-like
planet...
Finding methane may be a
sign on life, but we may need
other clues
How do we detect life on a dying planet?
New biosignatures?
There may be other fingerprints of life on a dying planet, e.g.
clouds...More science to be done!
The Time-line of Earth's future
1.0 billion
years
Brightening Sun raises temperatures
CO2 loss
Extinction of plants and animals
Runaway greenhouse
Microbes inherit the Earth
Ocean loss
2.8 billion
years
Planet gradually sterilised
Not necessarily the end of life in the
solar system...
Saturn's moon Titan is full of cold, organic material
Heating this up could give rise to a new origin of life