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Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

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Reminder: Homework #4 due Tuesday, 4:00 pm
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Page 1: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Reminder:

Homework #4 due Tuesday, 4:00 pm

Page 2: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

EVOLUTION OF ATMOSPHERES

Page 3: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

The dominant gasses arising from outgassing were

carbon dioxide and water vapor, with minor

amounts of nitrogen, sulfur, argon, …

Each terrestrial planet’s outgassed atmosphere

was roughly the same at the beginning.

Why do they differ now?

Page 4: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Mercury is too small and too

hot to hold onto an atmosphere.

Page 5: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Mars lost much of its atmosphere because of its

small size & lack of a magnetosphere.

Current atmosphere resembles its original atmosphere in

composition (essentially CO2).

The fate of its water is still a matter of debate. There appears to be substantial

amounts of subsurface frozen water.

Page 6: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Venus and the Earth:

started with more or less identical atmospheres.

Their atmospheres have subsequently followed very

different paths.

WHY?

Page 7: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Slightly higher temperatures at Venus’ distance from the Sun made it difficult for water to stay in liquid state.

Liquid water exists in abundance on the Earth

Carbon dioxide dissolves in oceans

Photosynthetic life creates oxygen (oxygen has a short lifetime in the atmosphere - must be constantly replenished).

Page 8: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

because of the Earth’s temperature: On Earth there are oceans

Original CO2 has dissolved into oceans

and is tied up in carbonate rocks, rocks (carbonates) keep levels of CO2 just balanced in atmosphere

keeps planet WARM but not HOT

if planet were hotter, CO2, H2O would

be boiled out of oceans and baked out of rocks more CO2, H2O enter Atmosphere

Evolution of Atmospheres:

Earth vs. Venus

Page 9: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Evolution of Atmospheres:

Earth vs. Venus

Liquid water may have existed early in Venus’ history – but most vaporized into atmosphere: T was hotter on Venus

H2O vapor is a greenhouse gas - trapped energy thus making planet hotter; eventually T so high that water boils

‘runaway’ because more H20 goes into the atmosphere as it evaporates; no water left on planet to dissolve CO2 – out of balance!

eventually stabilized when H20 broken down by UV sunlight (H escaped to space, O reacted with minerals) and there was no further CO2 to bake out of the Venus surface

Page 10: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

● This is called the runaway greenhouse effect

● It happened on Venus because Venus is closer to the Sun. We do not think it can happen on the Earth.

● So - Earth has less atmosphere because most of our CO2 is frozen in rocks (e.g., limestone)

Page 11: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Which of the following worlds has the most substantial atmosphere?

red) Mars blue) Earth yellow) Venus green) Mercury

Page 12: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Which of the following worlds has the most substantial atmosphere?

red) Mars blue) Earth yellow) Venus green) Mercury

The greenhouse effect keeps the temperature so high that essentially all of the CO2 remains in gaseous form

Page 13: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Earth's stratosphere is heated primarily by which process?

red) Ozone absorbs ultraviolet radiation.

blue) Atoms and molecules absorb infrared sunlight.

green) Greenhouse gases absorb infrared radiation.

yellow) Ozone absorbs visible sunlight.

Page 14: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

red) Ozone is broken apart by ultraviolet radiation.

Page 15: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

What Determines a Planet’s Surface Temperature?

In the absence of the Greenhouse Effect:

the planet's distance from the Sun the planet’s overall reflectivity

• the higher the albedo (reflectivity), the less light absorbed planet cooler

Page 16: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

What Determines a Planet’s Surface Temperature?

● With a greenhouse effect.

Greenhouse effect increases the energy (heat) in lower atmosphere, keeping the surface warmer

It works like a blanket

Page 17: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Greenhouse Effect on the Planets

● Greenhouse Effect warms Venus, Earth, & Mars on Venus: it is very strong on Earth: it is moderate on Mars: it is weak avg. temp. on Venus & Earth would be freezing

without it

Page 18: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

To Life!

Page 19: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

“Life” How is life defined? What is needed for life?

How hard it is for life to form?

What environments are suitable for life?

Page 20: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

How is “LIFE” defined?

Order - life has structure

This is extremely difficult. We can look at commonalities of what we have defined as living…

Page 21: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

How is “LIFE” defined?

Order - life has structure Reproduction Growth & development Energy utilization Senses & reacts to environment Evolutionary adaptation

This is extremely difficult. We can look at commonalities of what we have defined as living…

Page 22: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

All six properties of life are important, but biologists consider evolutionary adaptation to be the most important.

Evolution: “change with time”

Page 23: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Organisms need to be able to encode their structural information in order to reproduce.

In Earth-based life, this encoding is accomplished through DNA.

Page 24: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

DNA Replication

– Complete double helix– Strands separate into 2 helices– Two identical copies of the DNA in the cell– Cell division: one copy to each daughter cell

– Heredity: ensured by exact copying, but– Errors: occur occasionally -> evolution– Origin of Life: need simpler mechanism (RNA?)

Page 25: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Will Life Elsewhere Use DNA? Heredity and evolution are essential

DNA does the job on Earth today, but fairly complex

RNA may have been the first mechanism - simpler

No inherent reason the same complex mechanism is universal

Some type of molecule has to provide the mechanism for heredity and evolution

Page 26: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

ERRORS ARE IMPORTANT!

Changes (mutations) in this encoding will lead to changes in the organism.

Page 27: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Mutations and Evolution

Causes of mutations (errors in hereditary coding):– Ultraviolet (UV) light– Chemical agents (carcinogens)– Nuclear radiation (mostly natural cosmic rays)

Effect of mutations:– Harmless – no positive or negative consequences– Fatal– Evolution – survival & reproductive advantage

Page 28: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

If the change produces an organism better suited to its environment, it is more likely to be passed on, i.e., the

organism changes (evolves).

Page 29: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Natural selection

Artificial selection

Page 30: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

What are the necessities of life?

Nutrient source(s) – building blocks of organism Energy (sunlight, chemical reactions, internal heat) Liquid water (or possibly some other liquid)

Page 31: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Common Characteristics of Life?Carbon based

Have a protective membrane

Need liquid water

Use energy to maintain internal state

Can get energy from environment

Conduct metabolic processes (use stuff, make waste)

Responds to stimuli

Grow, reproduce (replicate)

Evolve and adapt to the environment as a population

Page 32: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Obtaining Energy

Living organisms can obtain energy through

“eating”, energy & nutrients from other organisms

extraction from chemical reactions in the environment (black smokers - ocean vents)

extraction from radiative energy (e.g., photosynthesis)

Page 33: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Metabolism

Page 34: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Why in cells? Chemical reactions much faster than in the open

Collects the raw materials for the chemical reactions

Provides the energy for the reactions

Provides enzymes to catalyze the reactions

Instructions for enzymes encoded in DNA

Metabolism: chemical reactions within living organisms. It takes place within cells.

Page 35: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Enzyme

A specialized substance that acts as a catalyst to regulate the speed of the many

chemical reactions involved in the metabolism of living organisms.

Without enzymes, life as we know it would not exist.

Page 36: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Metabolism and Cells Metabolism:

– Four forms of metabolism defined by:● Sources of carbon (direct or indirect)● Sources of energy (light or chemical)

– The four forms of metabolism are quite general and should apply to life anywhere

Cells:– Needed environment for metabolism at acceptable rate

Origin of Life (on Earth and elsewhere):– Look for cells as sites of metabolism

Page 37: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

● Carbon:– Heterotroph: eat other organisms– Autotroph: self-feeding by converting atmospheric CO2

● Energy:

– Photoautotrophs (plants): photosynthesis: CO2 + H2O + sunlight sugar

– Photoheterotrophs (rare prokaryotes): carbon from food but make ATP using sunlight

– Chemoheterotrophs (animals): energy from food

– Chemoautotrophs (extreme prokaryotes): energy from chemicals and not sunlight

Carbon and Energy Sources

Page 38: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Why Carbon based?

Can bond to as many as 4 atoms at a time. Can form skeleton of long chains of atoms

(polymers). The complexity of life requires complex

molecules.

Page 39: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Silicon can also form 4 bonds and is relatively abundant, however…

Bonds are weaker than those of carbon (fragile: complex Si-based molecules don’t last long in water)

Does not normally form double-bonds like Carbon; this limits the range of chemical reactions and molecular structures.

Carbon is more mobile in the environment - it can travel in gaseous form, e.g., CO2

Page 40: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Environmental limits to life (as we know it) ?

Is the planet of interest missing any of the key ingredients? (water, energy, nutrients)

Are temperatures below –15 or beyond +115 C?

Is it really cushy? – does it have an atmosphere

Page 41: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Importance of liquid water● Importance:

– Contact: organic chemicals float in the cell and find each other

– Transportation: bring chemicals in and out of cells– Participant in reactions, e.g.,:ATP, photosynthesis

● Necessity:– Life on Earth: all use water– Dormant without water: for a limited time only– Elsewhere: need a liquid (are there alternatives?)

Page 42: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Water

Liquid water plays a fundamental role in life:

Make chemicals available (dissolved) Transports chemicals Plays a role in many metabolic reactions

Page 43: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Cells All life on Earth is made of cells - microscopic units in

which living matter is separated from the outside world by a membrane.

All cells on Earth share common characteristics (e.g., use of ATP, DNA, …), leading to conclusion that they share a common ancestor

All cellular life is carbon based (organic molecules)

Page 44: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Components of Cells

Carbohydrates: energy needs and structures

Lipids: Source of energy & major component of

membranes. Lipids can spontaneously form membranes

in water.

Proteins: participate in a vast array of functions;

structural, enzymes, catalysts. Built from long chains of

amino acids.

Nucleic acids: instructions for reproduction

Page 45: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

70 amino acids known to

exist; only 22 are found in

life on Earth.

Only left handed versions

are found in living

organisms

Both of these traits

suggest a common

ancestor for life on Earth.

Page 46: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Based upon the cellular structure of an organism, living cells come in two types:

Prokaryotes

Eukaryotes

Page 47: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

The prokaryotes

simplest type of cell

lack a cell nucleus

Most are unicellular

two domains: bacteria &

archaea

asexual reproduction

many do not require free

oxygen

Page 48: Reminder: Homework #4 due Tuesday, 4:00 pm EVOLUTION OF ATMOSPHERES.

Eukaryotes

cells are organized into complex

structures enclosed within membranes.

Have a nucleus.

typically much larger than prokaryotes

May be unicellular, as in amoebae, or

multi-cellular, as in plants and humans.

both sexual and asexual reproduction


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