Life on Earth

What We Learn From Other Planetary Systems

• Protoplanetary Disks• Accretion of Planets• Expulsion and Migration of Planets• About 1000 extrasolar planets known• Our Solar System may be unusual?

Protoplanetary Disks in Orion

The Galactic Habitable Zone?

• Center: Too Violent, Stars too massive and short-lived

• Fringes: Not enough material to make suitable planets

• Middle: Stable but frequent star formation, expulsion of new material

Do We Need Jupiter for Life?

• Close-in Jupiter: other planets not possible• Jupiter in eccentric orbit: other planets won’t

have stable orbits• Distant Jupiter in circular orbit is a stabilizing

influence• Jupiter sweeps up a lot of potential impactors

Do We Need the Moon for Life?

• Moon’s gravity causes the earth’s axis to precess

• Mars’ axis tilt can be up to 60 degrees• Moon totally dominates effects of Sun and

other planets, keeps earth’s axis tilt within reasonable limits

“Of course, long before you mature, most of you will be eaten.”

“The picture’s pretty bleak,

gentlemen. The earth’s climate is

changing, the mammals are

taking over, and we all have brains

the size of a walnut.”

“Now this end is called

the thagomizer, after the late

Thag Simmons.”

“Evolution’s been good to you, Sid.”

Prebiotic Evolution

• The basic molecules of organic chemistry are easily made

• The first self-replicating molecule was almost certainly not DNA

• DNA assembles from simpler materials all the time

Plants and Animals

• CO2 + H2O + Energy = Sugars, Starches, etc. + O2 (toxic waste)

• O2 is actually toxic (even to us!)• Idea: Take the sugars and starches (from

somebody else) combine it with the waste O2, and get energy

Amazing Events in Life History• Sex - Who Needs It?• We are a team - Mitochondria• The Great Freeze 900-600 m.y. ago– What survived and how?

• Mass Extinctions– Dinosaurs = 4th worst– Permian extinction (220 m.y. ago) took out

90% of all species

Classification of Dogs and Humans• Kingdom Animalia• Phylum Chordata• Class Mammalia• Order Carnivora (Dogs) Primates

(Humans)• Family Canidae Hominidae• Genus Canis Homo• Species familiaris sapiens

Strigiphilus garylarsoni

“Actually, I considered this an extreme honor. Besides, I knew no one was going to write and ask to name a new species of swan after me. You have to grab these opportunities when they come along.”

The Five Kingdom System

• Animals• Plants• Protista (one-celled organisms)• Fungi• Bacteria*• Ediacaran Fossils? (ca. 700 m.y. ago)

What’s Bigger Than a Kingdom?• Bacteria differ from all other kingdoms in

lacking a cell nucleus• We need a bigger box• Superkingdoms or Domains– Monera (Bacteria)– Archaea– Eukarya (have cell nucleus)

• Need electron microscopes and molecular biology to see differences

Mass Extinctions

Impacts on Earth

Recent Impact – Meteor Crater

Manicouagan, Quebec

Sudbury, An Ancient Impact Site

A Shatter Cone

Fallback Breccia

Bessel: A Simple Crater

Ejecta around

Timocharis

Tycho: A Central-Peak

Crater

How Central Peaks Form

Upheaval Dome, Utah

Schrodinger: A Peak-Ring Crater

Mare Orientale A Multiple-Ring Impact

Basin

Impacts and Extinctions

• The problem isn’t killing things, it’s that anything survives.

• Immediate: Fireball, Blast, Ejecta• Hours: Tsunamis, Incoming ejecta• Days: Wildfires, Dust Cloud, Sulfur Aerosols• Months: Darkness, Death of plants and

animals, acid rain• Years: CO2 or Methane pulse?

Were The Dinosaurs Failures?

Dinosaurs: 150,000,000 yearsRecorded History: 5000 years• For every year of recorded history, the

dinosaurs had 30,000 years• For every day of recorded history, the

dinosaurs had 82 years• For every minute of recorded history, the

dinosaurs had three weeks