Lecture 9: Astrobiology

Question 1

Astrobiology?

Answer 1

Study of origins, evolution and future of life in the Universe including ET life and Earth.

Question 2

Did earth always have life?

Answer 2

No, life formed but where? We don’t know.

Question 3

History of Earth

Answer 3

Universe formed 14.6 Billion years ago.
Earths solar wind and solar system began around 5 Billion years ago.
Earth formed around 4.5 Billion years ago.
Life first became habitable around 3.9 Billions years ago.
First forms of life was around 3.9 - 3.5 Billion years ago.
Life possibly will be habitable for next 1 Billion to 2 billion years.

Question 4

Why Earth?

Answer 4

Earth has liquid water, protective atmosphere, in the habitable zone= right spot in the galaxy.

Question 5

Solar Habitable Zone.

Answer 5

Hypothetical distance from a star that can support life as we know it.
Here liquid water exists and this zone can change over a lifetime of a star.

Question 6

Galactic Habitable Zone

Answer 6

Too close to the center of galaxy: dangerous due to gamma ray bursts and supernovae.
Too far: no heavy matter like carbon.

Question 7

Liquid on other planets?

Answer 7

Mars, Europa: moon of Jupiter, Titan: moon of Saturn.

Question 8

Mars

Answer 8

Used to have a lot of liquid water,now only believed to have water.
Thin atmosphere, unprotected from solar radiation, geologically dead. Has disputed amount of methane.

Question 9

Europa

Answer 9

Moon of Jupiter, composed of rocks, Ice on the surface believed to have liquid water on the bottom.
Has oxygen in its atmosphere and strong tidal forces.

Question 10

Titan

Answer 10

Methane cycle is like our water cycle.
Has surface liquid methane and ethane.
Dense atmosphere, liquid on surface with wind and rain. Protected from solar wind my Saturn. Has complex organic molecules.

Question 11

Who can exist out there?

Answer 11

Chemolithotrophs could live on Europa and Titan.

Question 12

Extraterrestrial Hypothesis?

Answer 12

Life came from outer space.

Question 13

Panspermia

Answer 13

Hypothesis that life exists throughout the universe and dispersed by asteroids and meteorites.

Question 14

2 kinds of Panspermia?

Answer 14

Interplanetary: Between planets in solar system. Interstellar: Between stars.

Question 15

Interplanetary?

Answer 15

Large objects could hit planets dispersing rocks and microorganisms off into space.
These microorganisms could float away outside Earth & be carried by stellar wind.

Question 16

Evidence for Interplanetary?

Answer 16

Found around 53.000 meteorites from Mars and Moon on Earth.

Question 17

Interstellar?

Answer 17

Like interplanetary but much longer, driven by solar winds and gravity.

Question 18

Meteoritic Travel

Answer 18

Meteorites travel far, the inside doesn’t get too hot. Landing on a planet is easier than getting off a planet.

Question 19

Space Hazards

Answer 19

Desiccation: drying out of DNA
Ultra Violet Light: fragment and damage DNA Cosmic Rays: fast moving particles fragment and damage DNA.
Radiation: fragment and damage DNA.

Question 20

Radiation & DNA

Answer 20

High frequency radiation can knock of electrons off atoms.
Direct Route: Electrons are knocked off DNA
Indirect Route: Electrons can be removed from another molecule to create free radical that can damage DNA.
Radiation can break the backbone causing single or double stranded breaks.
Can break the hydrogen bonds between bases and damage the base and change them chemically.

Question 21

UV Light Causes:

Answer 21

Causes Thymine Dimers.

Question 22

Types of life suited for outer space?

Answer 22

Extremophiles and Spores!

Question 23

Extremophiles?

Answer 23

Organisms thriving in conditions that can kill most on Earth.

Question 24

Waterbears!

Answer 24

8 legged animal, live without water for up to 10 years, can survive extreme temperatures and pressures. Survive the vacuum of space.
Survive as much at 1000 times as much radiation as other organisms.

Question 25

Deinococcus Radiodurans

Answer 25

Most radiation resistant organism. Can survive 1.5 million rads and toxic environment. Survive desiccation, instead of hiding in spores they can repair its DNA from fragments, have multiple copies of its genome and DNA repair helps is survive desiccation.

Question 26

Exaption

Answer 26

Trait evolved for a certain function is helpful for another. The Deinococcus Radioduran evolved DNA repair for desiccation but now can be used against radiation stress. They can now survive outer space & space travel.

Question 27

Spores

Answer 27

Hard like seed, made by bacteria, fungi, plants, algae for DISPERSAL. Small and tough, dormant for millions of years and resistant against radiation.

Question 28

Bacterial Endospores

Answer 28

Not really spores cause not reproductively produced. DNA and protein surrounded by a protein coat, a place for bacteria to hide during rough times and when good, spores germinate. Don't need food, can survive high, freezing temperature, UV radiation, desiccation. Contains internal proteins that protects the DNA from UV damage. Have been isolated from inside rock. Germinated after 24-40 million years.

Question 29

So.. Panspermia is happening?

Answer 29

Interplanetary Panspermia is occurring right now, the methods and organisms exist! Panspermia, if interstellar makes life more prevalent in the Universe. Evolution also much easier. But life had to evolve somewhere...