September 10 th
What exactly are we looking for?
~we are searching for any sign of life. Defining life isn’t easy (even on earth).
~to being this search we tend to look for life as we know it. This does not mean that carbon
based life is the only life that exists. We must start somewhere.
~the notion of life beyond earth is an old theme but a little factual until recently. “Observations”
of canals on mars and jungles on Venus- both erroneous- advanced the notion of life in the solar
~ UFO’s tend to distort the search for evidence of life beyond earth. Macroscopic life does not
exist anywhere else except for the planet Earth. Many stars in our galaxy have planetary systems
meaning more potential signs for life.
2. Independent of observer
Hypothesis: limited validity to date
Model: Hypothesis verified in limited circumstances
Theory (Law): hypothesis confirmed by multiple experiments.
How does astronomy help us understand the possibility of extraterrestrial life?
~observational astronomy suggests that earth is not “special” and thus life may well exit
~Biology helps us understand the possibility of ET life by appreciating that a variety of life on
earth can be found on other planets.
~All science contributes to the search for life beyond earth, which all give insight into the search
Sept 12 2013
Astronomy has changed our perspective of the universe, giving rise to the correct interpretation
of “light in the sky” and the earth’s position in the universe (geocentric verses heliocentric solar
Ex. Testing the physics on the moon:Apollo 15 (YouTube video)
~Compares a hammer and a feather. In the gravitational field the hammer dropped at the
same speed as the feather because of the air mass that becomes the law of physics.
Planetary Science ~Gives context to where to find life
~1995 the first exoplanet was found.
~different planets, some habitable and some not.
~we have detected 1000 exoplanets. Suspected billions in the Milky Way galaxy. Trying to find
another planet compatible to earth (so called earth #2)
The Case of Life beyond Earth
~the building blocks for life on earth have been found elsewhere in the universe. These building
blocks are surprisingly common (organic molecules). Earth appears in history within 500 million
years of the planets formation. Earth is 4.5 billion years old.
Terrestrial Planets: Mercury, Venus, Earth, Mars (all have rocky surfaces).
Gogan Worlds: Jupiter, Saturn, Uranus, Neptune.
What are the conditions needed?
2. Source of heat
3. Enough time to develop a long chain of organic molecules
4. Protection from a lethal radiation environment
5. Earth is probably the most hospitable location to date but other candidates do exist close
6. Mars is a very likely candidate.
List of candidates
2. Europa (Jupiter’s moon)
3. Calisto (Jupiter’s moon)
4. Ganymede (Jupiter’s moon)
5. Titan (Saturn moon)
6. Enceladus (Saturn moon)
7. Triton (Neptune Moon)
Could Aliens be searching for us?
~SETI is one possible link to them (evidence for life does not necessarily mean evidence for
To the stars...
~Milky Way consists of 100+ billion stars.
~its 100,000 light years away.
~telescopic search for life is more particle. Radio telescopic search for signs is more intelligent
life capable of transmitting messages. We study the possibility of life because it is important for us to know that we are not alone. We seek the evidence Astrobiology aka exobiology or bio-
~conditions conductive to the origin and ongoing existence of life. Looking for the occurrence of
Life beyond Earth.
~How did attempts to understand the objects in and motion of the sky start us on the road to
Motion in the sky: Diurnal Motion
~the world rotates- making stars seem as if the sky and stars are moving around the world. Why?
People observed the great accuracy of the motion of the moon, sun, planets, and stars. They
noted the regularity of motions such as the sun setting in the west and rising in the east.
~Plato and Aristotle furthered this philosophy. At this time more weight was given to intuition
and thought then observation.
Further Development of Scientific Practices
~math was developed to help their discussions of the universe’s construction.
~Scientific method: correct sequence is: observe, hypothesis, predict, test, iterate.
*SUN RISES IN THE EASTAND SETS IN THE WEST
The Local Sky
~ An objects altitude (above horizon) and direction (along horizon) specify its location in your
~ Celestial sphere- objects altitude
~ Meridian= imaginary dome
Zenith: the point directly over your head. Straight up.
Horizon: all points 90⁰ away from zenith.
Meridian: line passing through zenith and connecting North and South points on the horizon.
Full circle= 360⁰
1 = 60⁰ (archminutes)
1′= 60” (arcseconds)
Describing the sky
~ It was Anaximander who suggested the notion of the celestial sphere, an imaginary construct to
help understand the motion of the sun, moon, planets, and stars. ~ Patterns of stars formed constellations.
The Geocentric Model
~ Eratosthenes determined the approximate diameter of the earth in about 240 BC.
~the 5 known planets (wanderers) plus the sun and moon moved across the celestial sphere. Days
were named after the moons and planets.
~ One of the most sophisticated geocentric model was that of Ptolemy (AD 100-170)
~Ptolemaic Model: sufficiently accurate to remain in use 100 years later.
Retrograde motion: the planets were moving at a point but the point was actually moved around
the sun. Planets move on its epicycle and deferent.
~Aristarchus: 240 BC suggested the sun was the center view of the universe.
~ The model offered a simpler idea to explain the cycle or retrograde motion.
~ Annual (stellar) Parallax (related to the apparent angular shift of the star) - two eye – your
brain telling you if something is too close or far etc. (this is called parallax) decreases.
September 19 th
~ During the period of science discovery, 2 schools of thought emerged concerning
1. TheAtomists who thought an infinite number of particles of earth, air, fire, and water
made up the universe.
~Democritus thought the planets are both “like and unlike” earth.
~Aristotle championed the opposing new namely that the characteristics of the 4 elements meant
that the earth had to be unique (and special) in the universe.
~ Planets move faster near the sun, and slower farther from the sun.
~ Sun centered model
~ He used the model to determine the layout and the solar system (1543)
~ AU= measurement of distance between earth and the sun.
~No more accurate than the Ptolemaic model.
~compared the most accurate (~/ arc min) naked eye measurements ever made of the planetary
~ Without parallax he was forced to believe that Copernicus might have been wrong. Kepler
~tried to make models work by he couldn’t. Ex. 8 arch minute.
EQUATION TO KEPLER’S 3 LAW: P₂= a₃
~ The straight line tells us that the square of each planet orbital period equals the cube of its
average distance from the sun.
a= 4 P=8
a₃= 4₃ P₂= 8₂
4₃= 64 8₂= 64
Galileo: Key Objections
1. Earth should not move because objects in the sky are left behind
2. Non- circular objects orbits aren’t perfect
3. If earth orbits the sun then why can’t we measure parallax
Using a telescope Galileo saw sunspots on the moon (imperfection) and also saw mountains and
valleys on the moon. He also found 4 moons around Jupiter.
~ Was put under arrest because he didn’t want to give up his belief that the sun is in the middle of
~Galileo showed that objects will stay in motion unless a force acts to slow them down
(Newton’s first law of motion).
How did Newton change our view of the Universe?
~Realized the same physical laws that operate on earth also operate in the heavens: one universe.
~conceived the laws of motion and gravity.
Newton’s 1 Law of Motion:
An object moves at a constant velocity unless a net force acts to changes its speed or direction.
Newton’s 2 Law of Motion:
Force = Mass x Acceleration
Newton’s 3 Law of Motion:
For every force there is always an equal and opposite reaction force.
What is gravity?
~ a force that keeps the moon in orbit about the earth, the planets moving around the sun, and a
force that keeps you firmly on the ground.
Universal Law of Gravitation:
1. Every mass attracts every other mass 2. The attraction is directly proportional to the product of their masses
3. The attraction is inversely proportional to the square of the distance between the
d₂ m₁ m₂
*on exam might ask how the equation behaves*
Einstein’s theory of relativity
An improvement on Newton’s law of gravity. The mass of the sun causes space time to curve.
So freely moving objects (such as planets and comets) follow the straightest possible paths
allowed by the curvature by space.
Copernicus bolds assertion of the heliocentric model to Newton’s mathematical portrayal of the
laws of motion and the law of gravity barley 150 years transpired. A revolution of ideas. Kepler
wrote a fiction story called “The Samnium”.
1. Simplicity is important (model)
2. Observation must be repeatable, verifiable.
3. Observation must be objective, free and bias
4. Beware of Pseudoscience claim such as those made by astrology. Astrologers make
predictions but they are no better than chance.
October 1 st
Universal context of life
Kepler’s 1 law states that planetary orbits are ellipses (clicker question).
~the element of life are widespread: carbon+ long chained organic molecules have been
detected through the galaxy. Physical law seems universal: the process of life could exist
1. Planet in our solar system
2. Solar system in our galaxy, Milky Way
3. Our galaxy in local group
4. The local group in the local supper cluster
5. All a part of the universe
A sense of scale: Planetary Distance
Many ways to visualize the size of our solar system. Recall the earth is 1 A(stromical) U(nit)
from the sun, 150 million km. Beyond the solar system: to the stars...
A light year (ly) is the distance a proton of light will travel in one year.
Alpha Centauri: our closest star system
~4.3 light years to Alpha Centauri (cen)
~if 1 AU= 1 meter than a cen= 271km
~voyager 1 (50,000km per hour) = 100,000 years to get there.
The ORION NEBULA is 1500(ly) away. Our galaxy is 100,000 light years away across and
home to over 200 billion stars and a lot of dark matter.
The Universe Contains
1. All matter and all energy
2. Matter you would recognize called baryonic matter 4%
3. Dark matter 28% (gravitational influence)
4. Rest of the universe 68% (dark energy)
The BIG BANG happened 13.8 billion years ago. The earth was compressed into a very hot,
very dense point and since that the universe continued to expand. Galaxy is in motion away
from the Milky Way.
The cosmic microwave background radiation- echoes of the big bang. The radiation associated
with heat has cooled over time.
~stars are created by galaxies by the collapse of clouds of hydrogen and helium (4 hydrogen
and 1 helium).
~heavier elements can be generated
~more massive stars live for shorter periods of time.
~stars can die quietly or with great fanfare.
~the pieces of stars are “reused” for new stars (stellar revolution) (star dust). October 15, 2013
~Nebula theory not the only hypothesis developed to explain our own solar system’s formation
but it is the theory that explains most observations.
~The variety of explanatory systems found to date have forced revisions and flexibility into the
nebula theory, the scientific method in action.
CLICKER QUESTION: which statement is incorrect?
Our Solar Structure system structure is the only stricter for other explanatory solar
Which of these facts are not explained by the nebular theory?
There are 4 terrestrial and 4 Jovian planets
Which object best describes an atom?
Electrons moving around the nucleus
Comparing gaseous carbon dioxide (CO2) TO SOLID CARBON DIOXIDE (DRY ICE),
WHICH STATEMENT IS TRUE?
Co2 molecules have less kinetic energy in the dry ice state.
Considering the electromagnetic spectrum, which statement is true?
Gamma radiation is more dangerous than radio frequencies.
Atoms, the building blocks of matter
~Atoms are composed by a positively charged nucleus containing protons and neutrons
surrounded by a negatively charged electron cloud (classical model).
~Most atoms around you are electrically neutral. If they gain or lose electrons, they become
charged and are referred to as ions.
~As the nucleus is very small, most atomic interactions arise through the electron cloud.
Atomic number=number of protons
Atomic mass number= number of protons +neutrons
*Different isotopes of a given element contain the same number of protons but different number
~Atoms can combine to form molecules. If 2 or more elements combine, it is called a compound.
H2O is the chemical formula for water ant it’s a compound.
~Molecules stay together because of the strength of the bonds between the atoms. Further, the
molecules stay close to each other by bonds as well. Temperature can change the phase of the
molecules. Organic molecules contain carbon
Compounds are molecules mode from atoms of two or more different elements.
Molecules consist of two or more atoms.
Gas Phase= atoms or molecules move essentially unconstrained.
Liquid Phase= Atoms or molecules remain together but move relatively freely.
Sold Phase= Atoms or molecules are held tightly in place.
**these are all forms of h2o regardless of the way atoms and molecules travel.
What Makes the Matter Move: Energy?
~Energy comes in different forms
~Kinetic energy is the energy of movement/ motion
~Radiant energy is the energy carried by light
~Potential energy is stored energy awaiting a use (as in to move or fall)
~Energy can transform from one type to another but it can neither be created nor destroyed
(always conserved). Forms of energy are transferable.
Light: the carrier of information
~Light carries energy at a speed of 3x10to the 8 m/per sec, the speed of light.
~it is essentially a combination of oscillating electric and magnetic fields, hence the term
~it is characterized by a wavelength and thus a frequency. Light displays wave-like properties
BUT carries energy in distinct packets called photons, a particle-like property.
Properties of Light
~The higher the frequency of light, the shorter the wavelength
~the higher the frequency, the more energy is called by the protons.
**Look over the Electromagnetic spectrum
Not all light reaches the Earth’s surface. Fortunately the most energetic frequencies are absorbed
by the gasses in the atmosphere.
Atmosphere scatters blue light from the sun, making it appear to come from different directions.
Sunsets are red because less of the red light from the sun is scattered.
Information from Light
~Distant objects emit light which we can receive and decode
~The intensity of light gives some information but analyzing the lights “fundamental
characteristics” or its spectrum reveals a great deal more information.
~3 types of spectrum exists: continuous, emission and abortion and all relate to different physical
October 22 nd Lighting at Home
Soft White: Color Temperature T= 2700k
Bright White: Color Temperature T= 3500-4100k
Daylight: Color Temperature T= 5000=6500k
The apparent change in wavelength of a was experienced by an observer that arises from the
relative motion of the source of the wave with respect to the observer (receiver).
What is a planet?
1. Orbits in the sky
2. Sufficient mass to be spherical in shape
3. Has cleared its planetary orbit of other objects
Since Pluto and a few others do not meet the 3 criteria they are defined as dwarf planets
*only applies to objects in our solar system
5 Terrestrial Worlds
4. Earth’s Moon
Characteristics of a Planet
1. Position in the solar system
2. Physical body and lithosphere in the universe
3. Magnetic field
4. Atmosphere (air) and Hydrosphere (water; oceans, lakes, rivers).
3 planet from sun
Water can exist in liquid state. If there is no atmosphere the water would be evaporated or
frozen. The atmosphere keeps the water in a liquid state. The habitable zone existence of
liquid water which is key factor in determining a habitable zone.
Orbit around the sun once a year
Distance from the sun varies only by a few %. This results in stable climate conditions.
Seasonal activity: because earth is tilted 23.5⁰ on its axis.
October 29 2013 December 15 – End of term exam: 10AM @ Rexall center
Earth- Active Surface
Since there are multiple convections currents between the earth’s surface crust is broken
up into places.
As well the plates can be moving alongside side one another in opposite directions
Finally the plates can be colliding as they move into one another (converging boundaries)
At spreading zones ...
Regions where one plate is sliding under another. Near these zones there tend to be strong
earthquakes, and explosive volcanic activity.
Where the plates are moving into one another one plate slides under the other- this is
called a subduction zone. This collision of plates creates mountain range.
This movement of the plates was initially referred to as continental drift but is now called
plate tectonics since the continent move with the entire plates.
As time passes and the plates move, the arrangement and climate of the continent will
change. 200 million years ago, all the continents were joined in a single continent. This
was called Pangaea
However they are still moving and some regions that are cold will eventually be in the
tropics, while some tropical regions will eventually become cold.
Not surprisingly this type of movement also affects evolution.
Earth’s magnetic field extends out 100,000s of km away from the surface of the earth.
The magnetic poles do not coincide with the axis of rotation, but they tend to drift around
and can reverse themselves entirely.
The magnetic field is important because it literally diverts most of the high energy
ionized particles of the solar wind away from earth, so it does not impact the surface and
affect life on the planet.
The field arises from the rotation of the earth and the liquid outer core that has electric
currents within it.
Ionized particles can be extremely damaging so this protection is very important for the
survival of life.
Some of the particles can flow along the magnetic field lines at the poles to interact with
our atmosphere and this produces the northern lights (Aurora Borealis).
Reading history in the rocks Knowing about rocks tells us a great deal about the physical process that are occurring on
a planet’s surface at the time.
(dark and dense, granite) this is rock that has formed from magma when it reached the
surface and cools (has melted and hardened)
Means the erosion occurs from water, wind glaciers etc. and rock is carried somewhere
else where it gets compacted into new rock such as limestone.
The details of the chemistry of the rock tells us which of the above erosive processes has
caused the deposition. This is how the presence of liquid water has confirmed by the
recent rovers spirit, opportunity and curiously on mars.
Most fossils are found in sedimentary rock layers (Grand Canyon).
Where the earth compresses and folds the rock with enormous pressure. We can see the
evidence of these stresses in the rock as it is bent and twisted (marble).
Mineralogical analysis: identifies minerals in the rock and ascertains the temperature and
pressure at the time of formation.
Chemical analysis: determines the identity of elements that make up the rock
Isotopic analysis: allow the environment at formation
The nucleus of a radioactive isotopes changes into another nuclei spontaneously. The
original nucleus is called the parent and the resulting nucleus is the daughter.
There can be multiple ways for an atom to decay from a parent to a daughter
Afossil is any evidence of the past life and rarely contains organic material.
Mineral replacements occurs and sometimes results in complete transformation
Less and less fossils exist the further back in time we go.
Eons, eras, periods, and ages help define the order and the development of events on
The Phanerozoic era: represents the most recent events in earth’s history and is the richest
fossil life. Earth’s Age
Oldest rocks we have on earth are 4.02 billion year
Minerals such as zircons suggest an age of 4.38 billion years.
Moon rocks have a maximum age determined to be 4.4 billion years old
Meteorites are determined to be 4.57 billion years old.
The Hadean Earth
Early earth was much hotter due to the heat of formation
Hadean era means “hellish” which means a harsh environment
Earth slowly cooled over time.An atmosphere and hydrosphere were needed for life to
Early atmosphere is nitrogen, carbon dioxide, methane, water vapor but virtually no
An atmosphere is the thin layer of gases held by a planet’s gravity. The layer of gases
generally extends up from the surface at the most a few hundred km.
Since gases are always in motion this means that they can escape.
Asmaller planet like earth cannot hold on to significant amounts of gases like hydrogen
Even in the earliest eras there would have been a significant amount of outgassing.
November 12 2013
If the earth’s axial tilt varies, so too will the stability of the climate change, potentially
CLICKER QUESTION: What object gives rise to Earth's axial stability?
Earth seems to have had a couple of super ice ages- so called snowball Earth’s where
most of the ocean’s surface froze over. These events occurred over 2.5 billion years and
800-600 million years ago.
It is significant to note that immediately after these periods there were large explosions in
the development of life particularly after the second event which ends about when the
Cambrian explosion starts.
These glaciations probably concentrated the materials needed for life, and “jump started”
the evolution process.
Dangers of human Activity
Human made CFC’s in the atmosphere destroy ozone, reducing protection from UV
radiation. Human activity is driving many other species to extinction.
Human use of fossil fuels produces greenhouse gases that can cause global warming.
Earth’s average temperature has increased by 0.5°C in the past 50 years.
The concentration of CO2 is rising rapidly.
An unchecked rise in greenhouse gases will eventually lead to global warming.
Global temperatures have tracked CO2 concentration for the last 500,000 years.
Antarctic air bubbles indicate the current CO2 concentration is at its highest level in at
least 500,000 years
Model Of Climate Change
Models of global warming that include human production of greenhouse gases are a better match
to the global temperature rise.
Nature of Life
One of the first problems to tackle in the search for life somewhere other than Earth
‘WHAT IS LIFE?’
This question has philosophical, religious and scientific aspects, but for the purpose of
this course we will stick to the science.
Restricting the Search
At the outset we need to set parameters to have a reasonable goal.
In this course we will focus on the nature of life SIMILAR TO OUR OWN
That is not to say other possibilities don’t exist, but there is a limit to how to deal with
this problem. It is easier to start with the familiar.
Life is made up of four main elements (and many other trace materials)
Carbon (C), Hydrogen (H), Oxygen (O) and Nitrogen (N): ~96%
Most of the oxygen and hydrogen in us is in the form of water (H2O)
Water is used in many ways by life. For example, plants use it in the photosynthesis
process, and it is used in other chemical processes
One of the most important uses is as a solvent. This includes it working as a transport
mechanism to distribute material throughout an organism.
Almost everything in this planet, at some level dissolves in water. It is the solvent properties
(transporting properties in water that are really important to us). Water is a polar molecule. This means one side (hydrogen) is slightly positive in charge,
while the other side (near the oxygen) is slightly negative in charge.
This is part of what makes it a good solvent.
The polarity arises from the way the covalent bond acts in the molecule. 19
7 Important Properties
1. Water is very abundant. There is lots of H(ydrogen) and lots of O(xygen) in the universe
so there is lots of water.
2. Water is very good at dissolving material so it can carry a lot of molecules of many
3. Water has a high heat capacity and a high vaporization energy. This is important because
cells use these properties to regulate temperature.
4. Water has a high surface tension. This helps keep a cell together, and pushes the
elements together in the first place (if you belly flop on water, one is able to see how hard
it really is. The water molecules are held close together).
5. Water breaks down when exposed to UV, and the O then forms ozone (O3), so it can
protect itself against UV. (this is important – UV rays destroy organic compounds)
6. Water floats when it freezes – ice insulates the water below it from freezing so life-forms
always have liquid water in which to survive.
7. Water is a liquid for a 100 degree Celsius temperature range (which is larger than other
materials we might consider as a solvent).
Life: Six Key Properties
Even for life on Earth this is a difficult definition to agree on.
What distinguishes a car from a cat for example?
We will use 6 key properties that life as we understand it should exhibit.
Note: each are aNECESSARY condition for lifBUT NOTASUFFICIENT condition for life.
1) Order or Structure: Pattern and structure by which organisms are put together.
Organisms of the same type have the same basic pattern. The variation between organism
results in different structures, but there must be some basic organization present.
2) Reproduction: Organisms can produce a copy of themselves - not necessarily identical,
but with most of the same characteristics, and are able to produce yet further generations.
Living organisms can be the product of reproduction even if they themselves cannot
reproduce. (eg Amule is sterile but the result of reproduction from a horse and a donkey.)
Viruses cannot reproduce by themselves. They can infect other organisms and generate
reproduction. Prions are abnormal forms of proteins that cause normal proteins to become
abnormal. They reproduce by causing alterations of other material.
3) Growth and Development: Organisms have the ability to grow and to develop from a
less organized state or simply to increase in size or both. Traits passed on to an organism from its “parents” is termed heredity. The heredity traits for life on Earth are carried by
4) Energy utilization: Any organism will need a source of energy to maintain its structure
and order and thus to reproduce and grow. There must be some mechanism by which an
organism can utilize a source of energy. Without energy, a system moves towards
disorder. Cars use gasoline but are not alive.
5) Response to Environment: Environments are always changing. This means organisms
have the ability to change and adapt as well. (This is on an individual level – like growing
a warmer fur coat for winter, or eyes contracting and expanding with changing light
levels). Athermostat responds to its environment but is not alive!
6) Evolution: This involves both the ability to reproduce and respond to the environment - it
is the change in the genetic makeup of an individual (off-spring) from its parents. These
changes can result in a survival advantage, so that eventually the new characteristic
Science likes classification, order that allows us to categorize observations.
Aspecies (specific) is a group of organisms with common genetic characteristics.
Genus (generic) species: ex. Homo sapiens (humans), Equus caballus (horses), Equus
Strictly speaking, evolution means “change with time”
The GreekAnaximander suggested 2500 years ago that life originated in water and
evolved from simple to complex forms.
Aristotle’s view, that became entrenched for 2,000+ years was that species were fixed
and independent and do not evolve (do not change)
Evolution and fossils
In the 1800s, Jean Lamarck suggested that fossils and living organisms were related by an
evolutionary process. Life adapted to its environment to “perform” successfully.
While in hindsight Lamarck was “on the right track”, it was left to Charles Darwin to
both postulate and find evidence for the Theory of Evolution. Charles Darwin (1809--1882). The voyage of the HMS Beagle led to the Theory of Evolution
and evidence to support the theory.
Theory of Evolution: Natural Selection
Overproduction and competition for survival: a given population in a confined area has
limited resources to survive.
Individual variation: No 2 individuals in a population are identical but rather vary in their
traits. Thus some individuals compete more effectively.
Inescapable conclusion: unequal reproductive success: the best adapted to survive,
Scientific theories need evidence
At the Galapagos Islands, differing islands have finch (bird) populations that have
obviously adapted to the local environments.
Similar relationships seen between fossils in certain areas/regions and present day
“variants” of the species.
Obviously Evolution at work in the Galapagos: adaptation for the various forms of life to
the local environment to grow and develop.
The mechanism of evolution
Evolution by natural selection means that species change and adapt by passing along
hereditary traits from one generation to another.
This is accomplished at the molecular level by the DNA(deoxyribonucleic acid)
November 19 2013
A definition of life
An entity (organism) that can reproduce and evolve through natural selection
Where does chemical evolution stop and biological evolution start?
By no means a perfect and all-encompassing definition but likely shared by all forms of
life, both terrestrial and extraterrestrial!
Cells: life’s basic building block
Cells are common to all forms of life, single celled or multi-cellular.Amembrane
encapsulates the inside cell material.
Cells pass on hereditary information via DNAmolecules.
All life on Earth shares a common ancestry having evolved from a common origin.
Carbon Humans are referred to as carbon based life, since the complex molecules we use to
structure ourselves are based on carbon compounds and the versatility of carbon bonding.
“Organic chemistry” is the chemistry of life and looks at the behaviour of compounds
that have as their basic building blocks C and H (hydrocarbons if only C and H).
Carbon can bond to 4 other atoms. This allows it to create very large and very complex 3
dimensional structures. This is what leads to the huge diversity of compounds that make
Bonds are strong enough to hold together well, but weak enough to break apart and
reform into other chemicals
Carbon shares with other elements. Life everywhere has to be carbon based. You cannot
build complex structures with anything else except carbon. Silicon may be alike, however
it fails ever other compound.
Silicon: like Carbon?
Silicon is another remote possibility for life as it can also form 4 bonds
BUT silicon bonds VERY strongly to oxygen (this is what rock is) and weakly to other
chemicals (like H). Long chain, more complex molecules not possible.
Silicon does not form double bonds and cannot form a gas (SiO2 versus CO2).
Silicon 1,000 more abundant on Earth than carbon yet carbon based life exists.
There are many other elements (about 20) that combine with C, H, N, O in DNAand thus
in cells. Calcium, phosphorous, potassium and sulphur the most common (and
important). That are used in much smaller amounts but are also crucial to life.
Is also very commonly part of organic chemicals as well as being present in water? O is a
very reactive chemical which makes it useful in energy transfer
Compounds are the joining of simple atoms into larger structures
The carbon compound building blocks and water (that life needs) turn out to very
common in the universe
Found in asteroids, comets, nebulae, planetary atmospheres, on and in planets and moons
Any two elements put together.
There are a number of different types of compounds that make up life (four of these are carbon
• These are mostly simple sugars like glucose (C6H12O6) used by cells for energy (and
• Additionally they can be used to create structure as well (like cellulose (C6H10O5)n in
2. Lipids (which includes fats) • Lipids in the form of fats also store energy.
• Their “carbon arrangement” (structures) makes them non-soluble in water.
• Spontaneously form membranes in water and thus in essence become the boundaries for
“chemical factories”. Likely essential in the early stages of the formation of life on
3. Proteins (made of amino acids)
• Work-horses of cells!
• Some proteins are structural elements, while others are enzymes (many other uses)
• Enzymes are molecules that catalyze chemical reactions in cells, allowing certain
biochemical reactions to occur (accelerate) including the copying of DNA. The enzymes
• Arise from the joining together of long chains of ~20 basic amino acids.
• 70 amino acids known but only 20 utilised by life (common ancestry?).
• Amino acids have a property of “handedness”, mirror images of the same molecular
• There is a right hand amino acid, and a left hand amino acid.
• Life on Earth only uses the Left arrangement. There doesn’t seem to be any reason – this
is just how things fell out.
• Both Left and Right forms are found in nature. Inorganic compounds have a mix of both
• Difference is detectable using polarized light.