1. Tree of Life
9 September 2016

2. Earth Extremes: possible analogies to other planets
Other Worlds
Earth Extremes: possible analogies to other planets
Hotsprings
The deep sea
Hypersaline environments
Evaporites
The atmosphere
Ice, permafrost, snow
Subsurface environments

3. Extremes on other planets
Other Worlds
Extremes on other planets
If we’ve seen life thrive in extreme circumstances on Earth, why not on other planets?
Mars holds most promise
What about moons in our solar system:
Europa
Titan
Enceladus

4. Europa Other Worlds Life exists w/o photosynthesis in the deep ocean
Europa has a subsurface ocean
Life may exist beneath the surface
Picture shows evidence of subsurface water!

5. Titan Airborne micro-organisms? Extremes to withstand: Other Worlds
Dessication
Radiation

6. Mars Host to several extreme environments Deserts
Other Worlds
Mars
Host to several extreme environments
Deserts
Ice, permafrost, snow
Subsurface

7. Mars: ice, permafrost, snow
Other Worlds
Mars: ice, permafrost, snow
Microbes and algae exist in frozen environments on Earth
Maybe not thriving, but microbial survivors could exist

8. Mars: subsurface environments
Other Worlds
Mars: subsurface environments
Best chance of withstanding Martian extremes
No liquid water at surface
Low pressure
CO2-rich atmosphere
Only 43% solar radiation at Earth
Subsurface provides
Protection
Possible liquid water
Energy source for chemolithoautotrophs

9. Summary
Earth life arose more than 3.5 billion years ago. Our oldest ancestors may have been extremophiles
Life has become progressively larger and more complicated, but large organisms are recent: 650 million years
Extremophiles live at high and low T, P, pH; high salinity and radiation
Earth’s extreme environments resemble other planets

10. The 3 Domains of Life

11. Origins of Earth life
Early Earth had abiotic environment with non-living organic chemicals
First life known had DNA, RNA, enzymes and proteins
All uses same gentic code

12. Key events in life history
Microbial evolution: first cells were anerobic and chemotrophic
Natural selection leads to rapid differentiation: mutations cause the tree of life to branch out
Photosynthesis uses solar energy and produces oxygen
O2 increases: crisis! Some evolved, others went extinct, some went to anerobic niches, eukarya develop

13. Eukarya Cell structures develop and specialize
Diverse forms, but all life was microbial until 1.2 billion years ago
Multicellular organisms lead to the Cambrian explosion

14. Tree of Life: All life is related
Evolutionary branches determined by DNA comparisons.
Bacteria seem most ancient; archaea closer to eukarya.

15. The Cambrian Explosion
Macroscopic life diversity “exploded” ~540 Myr ago:
Oxygen levels had risen: A good energy source!
But O2 attacks organic bonds: many microbes went extinct!
Soon after several Snowball Earths: coincidence or trigger?
Cambrian sea
Trilobite fossil

16. Colonization of the Land
For macroscopic life, protective ozone (O3) layer was vital step to inhabiting land:
Shields the surface from dangerous ultraviolet sunlight.
Life generated O2 (through photosynthesis), which forms O3, which protects life!

17. Impacts and extinctions
Played a key role
Ended species like the dinosaurs
A giant impact leads to a mass extinction
We can see craters on the Moon (no erosion) and Chicxulub crater in Yucatan
Pruned branches of the tree of life and allowed new species

18. Origin of Life: Summary
“Organic soup” vs. dilute solution.
Complex organics developed (mineral templates?).
“Pre-cells” enclosed complex organics.
Natural selection increased RNA complexity.
DNA developed within some successful cell(s).
A reasonable scenario, though many details are missing!

19. Summary
Earth life arose more than 3.5 billion years ago. Our oldest ancestors may have been extremophiles
Life has become progressively larger and more complicated, but large organisms are recent: 650 million years
3 domains of life: Bacteria, Archaea, Eukarya
All Earth life has a common ancestor