Transcript document

Life on Earth and on other worlds
• Prehistory: physical conditions for the
Universe to be life-friendly
• Life on Earth
• Chances for extraterrestrial life
• Search for other civilizations – are we alone in
the Universe?
Slide 1
Do we live in a special universe??
• Change of physical constants by a very small amount would
render impossible the life in the universe as we know it
• Adding or subtracting just one spatial dimension would make
the formation of planets and atoms impossible
• Life as we know it needs a universe which is large enough, flat,
homogeneous, and isotropic
Slide 2
Slide 3
Anthropic Principle
We observe the universe to be as it is because only in
such a universe could observers like ourselves exist.
That is, selection effects would say that it is only in universes where
the conditions are right for life (thus pre-selecting certain universe) is it
possible for the questions of specialness to be posed.
This is a solution, but can we do better?
Slide 4
Do we need a supernatural force?
How, and whether is it possible to cognize a real world?
Supernatural
explanation
Newton, Galileo, Kant, and many others:
Faith and scientific reasoning should not interfere
Slide 5
When any form of belief (religious, ideological etc. ) tries to solve scientific
problems, the progress is stopped, and only bad thing happen:
From inquisition (Giordano Bruno, Galileo) to prosecution of genetics, ban
on theory of evolution, quantum mechanics, etc.
Beliefs and rational thinking are two complementary
parts of human personality, but they should not replace
one another
Slide 6
History of science teaches us that there
is nothing special in the place we live
• Our local country is nothing special (ancient
travelers)
• Planet Earth is nothing special (Copernicus)
• Milky Way galaxy is nothing special (Hubble)
• Our part of the Universe is nothing special
– Self-reproducing Universe
– Eternal Big Bang and ensemble of universes
Linde, Vilenkin
Slide 7
Landscape of the multiverse
Planck scale:
Planck Length
Planck Mass
Planck density 1094 g/cm3
Slide 8
Life on Earth
Organization. All living things are organized and structured at the molecular, cellular,
tissue, organ, system, and individual level. Organization also exists at levels beyond
the individual, such as populations, communities, and ecosystems.
Maintenance/Metabolism. To overcome entropy (the tendency of a system to become
more disorganized and less complex), living things use energy to maintain
homeostasis (i.e., maintain their sameness; a constant, structured internal
environment). Metabolism is a collective term to describe the chemical and physical
reactions that result in life.
Growth. Living things grow. The size and shape of an individual are determined by its
genetic makeup and by the environment.
Response to Stimuli. Living things react to information that comes from outside or
inside themselves.
Reproduction. Individuals reproduce themselves. Life also reproduces itself at the
subcellular and cellular levels. In some instances, genetic information is altered. These
mutations and genetic recombinations give rise to variations in a species.
Variation. Living things are varied because of mutation and genetic recombinations.
Variations may affect an individual's appearance or chemical makeup and many
genetic variations are passed from one generation to the next.
Adaptation. Living things adapt to changes in their environment.
Slide 9
Physical basis of life on Earth:
the carbon atom!
Carbon can form long, complex, stable chains of atoms
Another shared property is that the proteins found in present-day
organisms are fashioned from one set of 20 standard amino acids.
These proteins include enzymes (biological catalysts) that are
essential to development, survival and reproduction.
Slide 10
Key property: information storage and
duplication
Replication agent: nucleic acids RNA and DNA
The genetic code specifies the amino acid sequences of all the
proteins each organism needs. More precisely, the instructions
take the form of specific sequences of nucleotides, the building
blocks of nucleic acids. These nucleotides consist of a sugar
(deoxyribose in DNA, and ribose in RNA), a phosphate group
and one of four different nitrogen-containing bases. In DNA, the
bases are adenine (A), guanine (G), cytosine (C) and thymine
(T). In RNA, uracil (U) substitutes for thymine. The bases
constitute the alphabet, and triplets of bases form the words.
Slide 11
Information Storage and Duplication
All information guiding all
processes of life are
stored in long spiral
molecules of DNA
(Deoxyribonucleic Acid)
Basic building blocks are
four Amino acids: Adenine,
Cytosine, Guanine, and
Thymine
Information is encoded in
the order in which those
amino acids are integrated
in the DNA molecule.
Slide 12
Processes of Life in the Cell
Information
stored in the
DNA in the
nucleus is
copied over to
RNA
(ribonucleic
acid) strands,
which acts as a
messenger to
govern the
chemical
processes in
the cell.
Slide 13
Duplication and Division
Slide 14
In the course of cell
division, the DNA
strands in the nucleus
(chromosomes) are
duplicated by splitting
the double-helix
strand up and
replacing the open
bonds with the
corresponding amino
acids
Process must be
sufficiently accurate,
but also capable of
occasional minor
mistakes to allow for
evolution.
When the earth formed some 4.6 billion years ago, it was a lifeless,
inhospitable place. A billion years later it was teeming with organisms
resembling blue-green algae. How did they get there? How, in short, did
life begin?
Slide 15
The Origin of Life on Earth
• Life develops into more complex forms through
gradual evolution, spanning many thousands of
generations.
• Life began in the
sea as single-celled
creatures.
• Those as well as
early multi-celled
creatures had no hard
parts to leave fossils.
Slide 16
Earliest, microscopic fossils
date back ~ 4 billion years.
Two advances of the 19th century
In one advance Louis Pasteur discredited the concept of spontaneous
generation. He offered proof that even bacteria and other microorganisms
arise from parents resembling themselves. He thereby highlighted an
intriguing question: How did the first generation of each species come into
existence?
The second advance, the theory of natural selection, suggested an
answer. According to this proposal, set forth by Charles Darwin and Alfred
Russel Wallace, some of the differences between individuals in a
population are heritable. When the environment changes, individuals
bearing traits that provide the best adaptation to the new environment
meet with the greatest reproductive success. Consequently, the next
generation contains an increased percentage of well-adapted individuals
displaying the helpful characteristics. In other words, environmental
pressures select adaptive traits for perpetuation.
Repeated generation after generation, natural selection could thus lead to
the evolution of complex organisms from simple ones. The theory therefore
implied that all current life-forms could have evolved from a single, simple
progenitor - an organism now referred to as life's last common ancestor.
Slide 17
Prehistory
Previous stars supplied heavy elements
Our Solar System has been formed with the Sun –
sufficiently long-lived star
One of the planets, the Earth, formed at a distance from the sun where
conditions were favorable and the necessary chemical ingredients were
available (note illustration's infalling comet and dust) for the origin of life.
Slide 18
The prebiotic earth: first billion years
Vigorous chemical activity is represented by
the heavy clouds, which were fed by
volcanoes and penetrated both by lightning
discharges and solar radiation. The ocean
received organic matter from the land and the
atmosphere, as well as from infalling
meteorites and comets. Here, substances
such as water, carbon dioxide, methane, and
hydrogen cyanide formed key molecules such
as sugars, amino acids, and nucleotides.
Such molecules are the building blocks of
proteins and nucleic acids, compounds
ubiquitous to all living organisms.
A critical early triumph was the
development of self-replicating RNA
molecule, which directed biological
processes and preserved life's "operation
instructions" for future generations.
Slide 19
The Miller Experiment
Miller Experiment in 1952: Simulating conditions on Earth
when life began ~ 4 billion years ago:
Experiment produced some
of the fundamental building
blocks of life: amino acids,
fatty acids, and urea.
Slide 20
Water (oceans), primitive atmosphere gases (hydrogen, ammonia,
methane), and energy from electric discharges (lightning).
The Origins of Life on Earth (3)
• Miller experiment shows that basic building blocks of
life form naturally.
• Amino acids and other organic compounds naturally
tend to link up to form more complex structures.
• Early oceans on Earth were probably filled
with a rich mixture of organic compounds:
the “Primordial Soup”
Slide 21
•Chemical evolution leads to the formation and
survival of the most stable of the more
complex compounds.
Extraterrestrial Origin of Life on
Earth
• Alternative theory: Most
primitive living entities
transported to Earth in
meteorites or comets.
• Some meteorites do
show traces of amino
acids.
• Theory of extraterrestrial
origin of life is currently
untestable.
Slide 22
Early evolution of life
Slide 23
Most of life's history involved the
biochemical evolution of single-celled
microorganisms. We find individual
fossilized microbes in rocks 3.5 billion
years old, yet we can conclusively
identify multicelled fossils only in rocks
younger than 1 billion years. The oldest
microbial communities often constructed
layered mound-shaped deposits called
stromatolites, whose structures suggest
that those organisms sought light and
were therefore photosynthetic. These
early stromatolites grew along ancient
seacoasts and endured harsh sunlight as
well as episodic wetting and drying by
tides. Thus it appears that, even as early
as 3.5 billion years ago, microorganisms
had become remarkably durable and
sophisticated!
Advanced life: last 500 million years
Trilobites – among the
first complex organisms
Slide 24
The Origin of Life on Earth (2)
~ 1/2 billion years ago, in
the Cambrian Period, the
diversity and complexity
of life on Earth
dramatically increased
“Cambrian Explosion”
Best-known fossils from
the Cambrian period:
Trilobites.
All known fossils from the
Cambrian period are from
sea creatures.
Slide 25
No traces of life on land until
~ 400 million years ago.
Geologic Time
In geologic
terms, higher life
forms, in
particular
mammals and
humans, have
evolved only
very recently.
Humans have
existed for only
~ 3 million years.
Slide 26
Three Questions About the
Evolution of Life
1) Could life originate on another world if
conditions were suitable?
Miller experiment etc. indicate: probably yes.
2) Will life always evolve toward intelligence?
If intelligence favors one species over another:
probably yes.
3) How common are suitable conditions
for the beginning of life?
 Investigate conditions on other planets and
statistics of stars in our Milky way
Slide 27
Habitable planet should have
a stable temperature regime and
a liquid to mix the essential building block elements together (carbon, hydrogen,
nitrogen, oxygen, phosphorus, sulfur, and transition metals like iron, chromium, and
nickel).
The planet should have a solid surface to concentrate the building block elements
together in the liquid on top. The more concentrated the solution of water and
molecules is, the more likely the molecules will react with each other. If the molecules
were fixed in a solid, they would not be able to get close to each other and react with
each other. If the molecules were in a gaseous state, they would be too far apart from
each other to react efficiently. Though the reactions could conceivably take place, they
would be rare!
The planet should also have enough gravity to keep an atmosphere.
Slide 28
Life in Our Solar System
Other planets or their moons are unlikely to have
ever provided suitable conditions for life.
Most promising
candidate: Mars.
Claimed
traces of
microscopic
fossils may
well be
regular
mineral
formations in
the rock.
Meteorite ALH84001,0 probably originated on Mars.
Slide 29
Possibly some evidence of past life on Mars, but questionable.
Jupiter’s Family of Moons
Over two dozen moons known now;
new ones are still being discovered.
Four largest moons already discovered by
Galileo: The Galilean moons
Io
Europa
Ganymede
Callisto
Interesting and diverse individual geologies.
Slide 30
Europa: heated internally, therefore the surface is soft
No vertical surface features can survive!
Surface is smooth as a skating rink
Slide 31
Fig. 18-10a, p.389
The Interior of Europa
Europa is too small to retain its internal heat  Heating
mostly from tidal interaction with Jupiter.
Core not molten 
No magnetic field.
Europa has a
liquid water
ocean ~ 15 km
below the icy
surface.
Slide 32
Titan
• About the size of Jupiter’s
moon Ganymede.
• Rocky core, but also large
amount of ice.
• Thick atmosphere, hiding
the surface from direct view.
Slide 33
Titan’s Atmosphere
Because of the thick, hazy
atmosphere, surface
features are only visible in
infrared images.
Many of the organic
compounds in Titan’s
atmosphere may have been
precursors of life on Earth.
Surface pressure: 50% greater
than air pressure on Earth
Surface temperature: 94 K (-290 oF)
 methane and ethane are liquid!
Methane is gradually converted to
ethane in the Atmosphere
 Methane must be constantly
Slide 34
replenished, probably through
breakdown of ammonia (NH3).
Slide 35
How Many Of Them Are Out There?
• 200 billion stars in the Milky Way
• Planetary systems are common
• However not all stars and all planets are
suitable for life!
Slide 36
Lifetime =
Amount of hydrogen fuel
Rate of energy loss
Lifetime T ~ M/L ~ 1/Mp-1 = 1/M2.5 ; p ~ 3.5
M = 4M;
T
 M sun 


Tsun  M 
star mass (solar masses)
Slide 37
2.5
1

32
time (years)
T ~ 3x108 years
Spectral type
60
3 million
O3
30
11 million
O7
10
32 million
B4
3
370 million
A5
1.5
3 billion
F5
1
10 billion
G2 (Sun)
0.1
1000's billions
M7
“Good” stars should live long: 0.5 to 1.4 solar masses
Binary stars are probably excluded
Only metal-rich Population I stars contain heavy elements
Slide 38
G and K stars are most suitable
Slide 39
Requirements for Life in Other
Planetary Systems
• Planetary systems are probably common.
• Stable orbit around the star  consider only single stars.
• Time for evolution  consider only F5 or less massive
stars.
• Moderate temperatures  Life zone around the star
Slide 40
The Drake Equation
Factors to consider when calculating the number of
technologically advanced civilizations per galaxy:
Nc = N* · fp · nLZ · fL · fl · FS
Most of the factors are highly uncertain.
Slide 41
Possible results range from 1 communicative civilization
within a few dozen light years to us being the only
communicative civilization in the Milky Way.
Other factors: global catastrophe
mass extinctions
Slide 42
Slide 43
Mass extinctions: once every ~ 100 million years
Asteroid or comet of 10 km size?
Slide 44
Impactor
Diameter
(meters)
Yield
Interval
(megatons) (years)
< 50
75
Slide 45
< 10
10 - 100
<1
Consequences
meteors in upper atmosphere most don't
reach surface
irons make craters like Meteor Crater; stones
1000 produce airbursts like Tunguska; land
impacts destroy area size of city
irons,stones hit ground; comets produce
5000 airbursts; land impacts destroy area size of
large urban area (New York, Tokyo)
160
100 - 1000
350
1000 10,000
15,000
700
10,000 100,000
land impacts destroy area size of moderate
63,000 state (Virginia); ocean impact makes big
tsunamis
1700
100,000 1,000,000
land impact raises dust with global
250,000 implication; destroys area size of large state
(California, France)
land impacts destroy area size of small state;
ocean impact produces mild tsunamis
150 known impact sites on the earth
Diameters from 50-70 m to 200 km
Slide 46
Barringer crater, Arizona
49,000 yr old
Iron meteorite of size 50 m, mass 300,000 ton
Impact velocity 11 km/sec
Over 30 tons of fragments found
Slide 47
Fig. 19-12b, p.426
The K-T Event and the Cretacious-Tertiary mass extinction
65 million years ago
Sixty-five million years ago, about 70 percent of all species then living on
Earth disappeared within a very short period in what is termed the
Cretaceous-Tertiary Mass Extinction---commonly known as the K-T Event
(K is used to denote the Cretaceous period rather than C to avoid
confusion with other periods such as the Cambrian). Among the species
that disappeared were the last of the dinosaurs. The cause of this and
other sudden species extinctions has long been an important and
controversial topic.
In 1980, physicist Luis Alvarez and coworkers reported finding a very high
concentration of the element iridium in the sedimentary clay layer laid
down at the time of the K-T extinction. On Earth, iridium is very rare in the
crust because it was concentrated in Earth's core when it was largely
molten. However, chondritic meteorites often still have the primordial solar
system abundances of these elements. This led Alvarez et al to suggest
that a chondritic asteroid 10 kilometers in diameter that struck the Earth in
the K-T period would contain enough iridium to account for the worldwide
clay layer iridium enhancement, and that this meteor impact could also
have triggered dramatic climatic changes that produced the K-T extinction.
Slide 48
K/T boundary clay layer (Italy)
Places where the sediments were found
Slide 49
Further evidence:
Sites near the Brazos River in Texas show a thick layer of unusual
sediment immediately underneath the iridium layer. This sediment was
formed by a massive tsunami (tidal wave), caused by the impacting
object.
Sites in Beloc, southern Haiti, also show tsunami debris together with
large quantities of ejected material such as shocked quartz and
tektites.
tectites
Slide 50
spherules
Shocked quartz
Slide 51
Fig. 19-13b, p.426
Gravity anomaly over the Chicxulub crater
Slide 52
• World-wide fires
• 1-km-hign tsunamis
• Acid rains and atmospheric pollution
• Darkness and severe winter for many decades
Slide 53
Sandia simulation of 1-km asteroid hitting the Atlantic near New York
15 deg grazing impact
Distant and head-on view at .4 seconds after impact
Orange: above 5000o C
Distant and head-on view at 2.4 seconds after impact
Distant and head-on view at 8.4 seconds after impact
Slide 54
What is the current statistics?
Slide 55
Remains of a failed planet?
2.8 AU from the Sun
Slide 56
Earth-crossing asteroids
By estimate, the entire population of Earth-crossing asteroids
includes some 1500 larger than one kilometer and 135,000 larger
than 100 meters in diameter.
Toutatis: one of the closest. 5 km diameter
Next close flyby: 29 Sept. 2004, 4 lunar distances from Earth
Slide 57
Potentially Hazardous Asteroids (PHAs) are those with an
Earth Minimum Orbit Intersection Distance (MOID) of 0.05 AU or less
and an absolute V-magnitude of 22.0 or higher (indicating that they
are greater than around 100m across). Most PHAs are detected after
they have already passed the Earth.
On August 7 1994, asteroid 1994 XM1 reached a minimum distance
of 0.0026 AU (112000 km) from the Earth. This object is estimated to
be about 10 m across. If it had collided with the Earth, the impact
energy would have been equivalent to about four Hiroshima bombs.
The resulting crater would have been hundreds of metres across devastating to a major city.
The closest known forthcoming approach will be on 7 August 2027
when a PHA will pass within 0.0024 AU (roughly 360,000 km) from the
Earth. This is less than the distance from the Earth to the Moon.
Slide 58
The Peekskill meteorite
October 9, 1992
12 kg chondrite meteorite reached the earth
Slide 59
Are we a communicative civilization?
• Not really …
Slide 60
A message in a bottle cast into the
cosmic sea
12-inch gold disk carried by Voyagers I and II
Slide 61
Communication with Distant Civilizations
• Direct space travel to other stars not feasible due to large
distances (long travel times).
• Viable alternative: Radio communication.
• Even for radio communication: Long answer times
due to light-travel time.
• Messages can be arranged in blocks of certain length
that is a product of two prime numbers  Only two ways
to arrange them in a rectangle.
Slide 62
Arecibo Radio Telescope
In 1974 Arecibo sent a message to the globular
cluster M13 in Hercules (300,000 stars)
Slide 63
The Arecibo Message
At dedication
of Arecibo
Radio
Observatory,
blocks of
1679 pulses
were emitted,
which can be
arranged in
only two
ways:
23 rows of 73
or 73 rows of 23.
Slide 64
Resulting 23 x 73 grid
contained basic information
about our human society.
Distance to M13 is 25,000 ly
Slide 65
Search for Extraterrestrial Intelligence
SETI
• Searching for radio signals in the microwave
range
• Annual cost = the cost of a helicopter
• Yet there is no funding from any government
Slide 66