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Backman Seeds Ghose Milosevic-Zdjelar Read
Prepared by:
Jennifer West
Department of Physics and Astronomy
University of Manitoba
Chapter 14 and 15
Outer Solar System
and
Life on Other Worlds
1
Neptune
Beyond Uranus lies the outermost major planet in our
solar system, Neptune. It wasn’t discovered
accidentally!
Remember the Titius-Bode rule?
a = (4+ 3×2n)/10 AU
n=1 a=1 AU real distance 1 AU
n=2 a=1.6 AU
--,,-- 1.52 AU (Mars)
n=3 a=2.8 AU
--,,-- 2.77 AU (Ceres, 1801, Piazzi)
n=4 a=5.2 AU
--,,-- 5.2 AU (Jupiter)
n=5 a=10 AU
--,,-- 9.58 (Saturn)
n=6 a=19.6 AU
--,,-- 19.23 (Uranus, 1781,
Herschel)
n=7 a=38.8 AU ???
2
Neptune
The predicted distance to the next hypothetical planet would
be ~39 AU according to T-B ‘law’. The search was on, but
the predicted distance didn’t make the discovery any easier.
• Two astronomers independently calculated the location of
Neptune from irregularities in the motion of Uranus (inspired
by a hypothesis of Alexis Bouvard).
•British astronomers were a bit slow to respond
to calculations of John C. Adams. In the 20th
century one of them stole the evidence of how
inaccurate the predictions of Adams were.
•Urbain Le Verrier (On Sept. 23, 1846,
Neptune was discovered by J. Galle
within a few degrees of where he had
predicted it to be on the sky)
3
Neptune
Remember the Titius-Bode rule? It failed at Neptune!....
a = (4+ 3×2n)/10 AU
n=1 a=1 AU real distance 1 AU
n=2 a=1.6 AU
--,,-- 1.52 AU (Mars)
n=3 a=2.8 AU
--,,-- 2.77 AU (Ceres, 1801, Piazzi)
n=4 a=5.2 AU
--,,-- 5.2 AU (Jupiter)
n=5 a=10 AU
--,,-- 9.58 AU (Saturn)
n=6 a=19.6 AU
--,,-- 19.2 (Uranus, 1781, Herschel)
n=7 a=38.8 AU
--,,-- 30.1 AU (Neptune, 1846, Galle)
Right now, we know that most extrasolar planetary systems do not obey
any strict mathematical spacing laws.
4
Neptune
• Neptune looks like a tiny blue dot with no
visible cloud features.
• Thus, astronomers named it after the god of the
sea.
• In 1989, Voyager 2 flew
past and revealed some
of Neptune’s secrets
5
Planet Neptune
• Neptune is almost exactly the same size
as Uranus.
• It has a similar interior too.
• A small core of heavy elements lies within a
slushy mantle of water, ices, and minerals
(rock) below a hydrogen-rich atmosphere
6
Planet Neptune
However, Neptune looks quite different.
• It is bluer
• It has active
cloud
formations.
7
Planet Neptune
• The dark-blue tint to the atmosphere is understandable.
Its atmosphere contains 1.5 times more methane than
Uranus.
8
Planet Neptune
• Methane (CH4) absorbs red photons better
than blue and scatters blue photons better
than red.
• This gives Neptune a blue colour and Uranus
a green-blue colour.
9
Planet Neptune
• When Voyager 2 flew by Neptune in 1989,
the largest feature was the Great Dark Spot.
• Roughly the size of Earth, the
spot seemed to be an
atmospheric circulation –
much like Jupiter’s Great
Red Spot.
• Smaller spots (hurricanes)
are present
10
Planet Neptune
• Recently, the Hubble Space Telescope
photographed Neptune and found that the
Great Dark Spot is gone and new cloud
formations have appeared.
• Evidently, the weather on Neptune is
changing.
11
Planet Neptune
• The atmospheric activity on Neptune is
apparently driven by heat flowing from the
interior plus some contribution from dim light
from the Sun 30 AU away.
• Neptune may have more atmospheric
activity than Uranus because it has more
heat flowing out of its interior.
• The reasons for this, though, are unclear.
12
Planet Neptune
• Like Uranus, Neptune has magnetic field
that must be linked to circulation in the
interior.
• In both cases, astronomers suspect that
ammonia dissolved in the liquid water mantle
makes the mantle a good electrical conductor
13
The Neptunian Moons
• The two largest moons (out of 13) have
peculiar orbits.
• Nereid, about a tenth the size of Earth’s
moon, follows a large, elliptical orbit –
taking nearly an Earth year to circle
Neptune once.
• Triton, nearly 80 percent the size of
Earth’s moon, orbits Neptune backward,
clockwise as seen from the north.
14
Neptune with moon Triton
15
The Neptunian Moons
• These odd orbits suggest that the system
was disturbed long ago in an interaction
with some other body, such as a massive
planetesimal.
16
The Neptunian Moons
• With a temperature of 37 K, Triton has an
atmosphere of nitrogen and methane
about 105 times less dense than Earth’s.
17
The Neptunian Moons
• A significant part
of Triton is ice.
• Deposits of nitrogen
frost are visible at
the southern pole.
18
The Neptunian Moons
• Many features on Triton suggest it has had
an active past.
• It has few craters, but it does have long faults
that appear to have formed when the icy crust
broke.
• Also, there are large basins that seem to have
been flooded repeatedly by liquids from the
interior.
19
The Neptunian Moons
• Even more interesting are the dark smudges
visible in the southern polar cap.
• These are interpreted as sunlight-darkened
deposits of methane erupted out of liquid nitrogen
geysers.
20
The Neptunian Rings
• Neptune’s rings are faint and very hard to
detect from Earth.
•
•
•
•
Maybe seen in 1846 by Lassell (discoverer of Trition))
Recorded in 1968 stellar occultation but missed
Found in 1984 (occultation)
Imaged 1989 (Voyager 2)
21
The Neptunian Rings
• 5 Neptune’s rings, named after the astronomers
involved in the discovery of the planet, are similar
to those of Uranus, but contain more dust relative
to stones
• The moon Galatea is gravitationally producing short,
incomplete arcs in the outermost ring, called
• Egalite, Fraternite, Liberte, Courage
22
The Neptunian Rings
• The Egalite, Fraternite, Liberte, Courage,
• the semi-transparent arcs are changing their brightness
and some are shifting the azimuthal position.
• In 2003 Liberte disappeared
23
The Neptunian Rings
• The rings are a bit mysterious: some have been
observed to consist of braids like a rope
• Their dynamics (mechanics of arcs) is not yet fully
understood
• The rings are semi-transparent, they absorb less than
10% of light passing through them
24
Pluto: Planet No More
• Out on the edge of the solar system orbits
a family of small, icy worlds.
• Pluto was the first to be discovered, in 1930.
• However, modern telescopes have found more.
25
Pluto: Planet No More
• Out on the edge of the solar system orbits
a family of small, icy worlds.
• Pluto was the first to be discovered, in 1930.
• However, modern telescopes have found more.
•Hubble Space Telescope view of
• Pluto and its moon Charon :
26
Pluto: Planet No More
• You may have learned in school
that there are nine planets in our
solar system.
• However, in 2006, the
International
Astronomical Union voted to
remove one of them, Pluto,
from the list of planets.
27
Pluto: Planet No More
• Its orbit is highly inclined and so elliptical
that it actually comes closer to the Sun
than Neptune at times.
28
Pluto: Planet No More
•To understand Pluto’s status, you must use
comparative planetology to analyze Pluto and then
compare it with its neighbours.
29
Pluto: Planet No More
• Pluto is very difficult to observe from Earth.
No space probes visited it yet
• It has only 65% of the diameter of Earth’s Moon.
In Earth-based telescopes, it never looks like
more than a faint point of light, but some features
are seen by the HST
30
Pluto – a dwarf planet
31
Pluto: a dwarf planet
• Orbiting so far from the Sun, it is cold
enough to freeze most compounds you
think of as gases.
• Spectroscopic observations have found
evidence of nitrogen ice.
• It has a thin atmosphere of nitrogen (N2) and
carbon monoxide (CO) with small amounts of
methane (CH4)
32
Pluto: a dwarf planet and its moons
• Pluto has three five moons.
• Two – Nix and Hydra – are small.
• Charon, though, is relatively large – half
of Pluto’s diameter.
33
Pluto and Charon
• Charon orbits Pluto with a
period of 6.4 days in an
orbit highly inclined to the
ecliptic.
• Pluto and Charon are tidally
locked to face each other.
• So, Pluto’s rotation is also
highly inclined
34
Pluto: a dwarf planet
• Charon’s orbit size and period plus Kepler’s
third law reveal that the mass of
the system is only about 1/500 of
Earth mass.
• Most of the mass is Pluto –
about 12 times the mass of Charon
•
•
•
•
•
Historical mass estimates for Pluto
1931: 1 Earth
1948: 1/10 Earth
1976: 1/100 Earth
1978: 1/500 Earth
35
Pluto
• Knowing the diameters and masses of Pluto
and Charon allows astronomers to calculate
that their densities are both about 2 g/cm3.
• Thus, Pluto and Charon must contain about
35% ice and 65% rock.
36
What Defines a Planet?
• To understand why Pluto is no longer
considered a planet, you should recall the
Kuiper belt.
• Since 1992, new, large telescopes have found a
thousand icy bodies orbiting beyond Neptune.
• There may be as many as 100 million objects in
the Kuiper belt larger than 1 km in diameter.
They are understood to be icy bodies left over
from the formation time of the outer solar system.
37
What Defines a Planet?
• Some of the Kuiper-belt objects are quite
large.
• One, named Eris, is 5 percent larger in
diameter than Pluto.
• Three other Kuiper-belt objects found so far –
Sedna (named after the Inuit sea goddess),
Orcus, and Quaoar – are half the size of Pluto
or larger.
38
Pluto: Planet No More
• Its orbit is highly inclined and so elliptical
that it actually comes closer to the Sun
than Neptune at times.
39
TNOs – Trans-Neptunian Objects
• Many of these objects have moons of their
own.
• In that way, they
resemble Pluto and
its moons.
40
What Defines a Planet?
• Comparative planetology shows that Pluto
is not related to the Jovian or terrestrial
planets.
• It is a member of a newfound family of icy
worlds that orbit beyond Neptune, much
larger than comets.
41
What Defines a Planet?
• One of the IAU’s criteria for planet status is that an
object must be large enough to dominate and
gravitationally clear its orbital region of most or all
other objects. Pluto does not meet the criterion.
42
What Defines a Planet?
• Eris (formerly called Xena) and Pluto – the
largest objects found so far in the Kuiper belt –
do not meet the standard.
Eris and its moon Dysnomia
Neither does Ceres, the largest body in the asteroid belt.
43
What Defines a Planet?
• However, all three (Pluto, Eris, Ceres) are
large enough for their gravity fields to have
pulled them into spherical shapes. (That’s a
requirement for a planet.)
• Hence, they are the prototypes of a new
class of objects defined by the IAU as dwarf
planets.
44
Pluto and the Plutinos
• Over a dozen Kuiper-belt objects are known
that are caught with Pluto in a 3:2 resonance
with Neptune.
• That is, they orbit the Sun twice, while Neptune
orbits three times.
• These Kuiper-belt objects have been named
plutinos.
• how were they caught in resonances?
45
Pluto and the Plutinos
• Models of the formation of the planets
suggest that Uranus and Neptune may have
formed closer to the Sun.
• Sometime later, gravitational interactions
among the Jovian planets could have gradually
shifted Uranus and Neptune outward.
• As Neptune migrated outward, its orbital
resonances could have swept up small objects
like a strange kind of snowplow.
46
Pluto and the Plutinos
• The migration of the outer planets would
have dramatically upset the motion of
some of these Kuiper-belt objects.
• Some could have been thrown inward,
where they could interact with the Jovian
planets.
• Some may have been captured as moons
(Triton?)
47
Pluto and the Plutinos
• Other objects may have impacted bodies
in the inner solar system and caused the
late heavy bombardment episode
especially evident on the surface of
Earth’s moon.
• The small frozen worlds on the fringes of
the solar system may hold clues to the
formation of the planets 4.6 billion years
ago.
48
Chapter 15 -- Life in the Universe
• The atoms of carbon, oxygen, and other
heavy elements that are necessary
components of your body did not exist at
the beginning of the universe.
• They were created by successive generations
of stars.
• We are made of stardust
49
• The elements from which you are made are
common everywhere in the observable
universe. As a matter of fact, both you and
your planet consists mostly of one element
(by mass). Do you know which?
• So, it is possible that life began on other worlds
and evolved to intelligence there as well.
• If so, perhaps these other civilizations will be
detected from Earth.
50
Your goal in this lecture is to try to understand the
most intriguing of puzzles – the origin and evolution
of life on Earth and (in the next lecture) possibly the
other worlds.
51
The Nature of Life
• What is life?
Life is a process by which an organism extracts
energy from the surroundings, maintains
itself, and modifies the surroundings to
promote its own survival and reproduction.
52
The Physical Basis of Life
• The physical basis of life on Earth is the element
carbon (C).
• Due to the way carbon atoms bond to each other and to
other atoms, they can from long, complex, stable chains
that are capable of storing and transmitting information.
• Life needs to store a large amount of information
•
hydrocarbons
53
The Physical Basis of Life
• Carbon may not be absolutely necessary to life.
• Silicon could in principle be substituted for carbon
because the two elements share some chemical
properties.
• However, this seems unlikely because silicon
chains are harder to assemble and disassemble
than their carbon counterparts and can’t be as
long.
• J. Haldane, "The Origins of Life", New Biology, 16,
12–27 (1954). Suggested that an alternative
biochemistry could be based on liquid ammonia.
54
The Physical Basis of Life
• Even stranger life forms have been proposed
based on electromagnetic fields and ionized
gas.
• None of these possibilities can be ruled out
• These hypothetical life forms make for fascinating
speculation
• However, only a speculation….
55
The Physical Basis of Life
• Even carbon-based life has its mysteries.
• What makes a lump of carbon-based
molecules a living thing?
• An important part of the answer lies in the
transmission of information from one molecule to
another.
56
Information Storage and Duplication
• Almost every action performed by a living cell
is carried out by chemicals it manufactures.
• Cells must store recipes for all these chemicals,
use the recipes when they need them, and pass
them on to their offspring without too much error.
• Hence Deoxyribonucleic acid (DNA), a digital
code transmitter
• Analog transmission of information, not in the form of a
symbolic code but, say, proportions of chemicals would
not support life on Earth
57
Information Storage and Duplication
• There are three important points to note about
DNA.
58
Information Storage and Duplication
One, the chemical recipes of life are stored in
each cell as information on DNA molecules.
• These molecules resemble a ladder with rungs that
are composed of chemical bases: A, C, T (U), G
• Adenine, Cytosine, Thymine (alt.: Uracil), Guanine
The recipe information
is expressed by the
sequence of ladder
rungs, providing
instructions to guide
chemical reactions
within the cell.
Information Storage and Duplication
• Two, DNA instructions normally are expressed
by being copied into a messenger molecule
called RNA that causes molecular units called
amino acids to be connected into large
molecules called proteins.
• Proteins made of amino acids
serve as the cell’s basic
structural molecules or as
enzymes that control chemical
reactions.
Information Storage and Duplication
• Three, the instructions stored in DNA are genetic
information passed along to offspring. (One strand
calles chromosome can have 220 millions of
nucleotides)
• The DNA molecule reproduces itself when a cell divides;
Information Storage and Duplication
• To produce viable offspring, a cell must be
able to make copies of its DNA.
• Surprisingly, it is important for the continued
existence of all life that not all the copies be
exact duplicates.
62
Modifying the Information
• Earth’s environment changes
continuously.
• To survive, species must change as their food
supply, climate, or home terrain changes.
• If the information stored in DNA could not change,
then life would quickly go extinct.
• The process by which life adjusts itself to its
changing environment is called biological
evolution.
63
Modifying the Information
• When an organism reproduces, its offspring
receives a copy of its DNA.
• Sometimes external effects such as radiation alter
the DNA during the parent organism’s lifetime, and
sometimes mistakes are made in the copying
process.
• 40-50 nucleic acids are damaged per DNA molecule
per second, when you sunbathe. The damage is
mostly repaired by proteins. In any case, any dmage
is not passed on to offspring.
• This is an example of mutation, which can also
occur due to viruses or chemicals.
64
Modifying the Information
• Most mutations make no difference.
• Some, however, are fatal, killing the afflicted
organisms before they can reproduce.
• In rare but vitally important cases, a mutation can
actually help an organism survive.
65
Modifying the Information
• These changes produce variation among
the members of a species.
• All the squirrels in the park may look the same
but they carry a range of genetic variation.
• Some may have slightly longer tails or fastergrowing claws.
66
Modifying the Information
• These variations make almost no
difference until the environment changes.
• If the environment becomes colder, a squirrel
with a heavier coat of fur will, on average,
survive longer and produce more offspring
than its normal contemporaries.
• Similarly, the offspring that inherit this beneficial
variation will also live longer and have more
offspring of their own.
67
Modifying the Information
• These differing rates of survival and
reproduction are examples of natural
selection.
• Over time, the beneficial variation increases in
frequency, and a species can evolve until the
entire population shares the trait.
• In this way, natural selection adapts species to
their changing environments – by selecting, from
the huge array of random variations, those that
would most benefit the survival of the species.
68
Modifying the Information
• It is a common misconception that
evolution is random, but that is not true.
• The underlying variation within species is
random.
• Natural selection, though, is not random
because progressive changes in a species
are directed by changes in the environment.
69
Life in the Universe
• It is obvious that the 4.5 billion chemical
bases that make up human DNA (in each
cell) did not just come together in the right
order by chance.
• The key to understanding the origin of life lies
in the processes of evolution.
70
Life in the Universe
• This means that life on Earth could have
begun very simply, even as simple a form
as carbon chain molecules able to copy
themselves.
• Of course, this is a hypothesis for which you
can seek evidence.
• What evidence exists regarding the origin of life on
Earth?
71
The Origin of Life on Earth
• The oldest fossils are all the remains of
sea creatures.
• This indicates that life began in (or was
brought into) the sea.
• However, identifying the oldest fossils is not easy.
72
The Origin of Life on Earth
• Fossils billions of years old are difficult to
recognize because the earliest living things
contained no easily preserved hard parts like
bones or shells.
• They were
microscopic
Bacteria & Archea
The Origin of Life on Earth
• Fossils from western Australia that are more than
3 billion years old contain features that experts
identify as stromatolites – fossilized remains of
colonies of single-celled organisms, such as
cyanobacteria.
The Origin of Life on Earth
• The evidence, though scarce, indicates that
simple organisms lived in Earth’s oceans
3.4 Gyr ago – less than 1.2 billion years
after Earth formed. Chemical signs of life exist
back to 3.8 Gyr ago, 0.75 Gyr after the Earth fully
formed
• Where did these simple organisms come from?
• Alexander Oparin (1896-1980) thought in 19231936 that they formed on Earth, in a
primordial soup rich in hydrogen, methane
and ammonia.
75
The Origin of Life on Earth
• An important experiment performed by
Stanley Miller and Harold Urey in 1952
sought to recreate the conditions in which
life on Earth might
have begun.
The Origin of Life on Earth
• The Miller experiment consisted of a sterile,
sealed glass container holding water, hydrogen,
ammonia, and methane.
• An electric arc inside
the apparatus created
sparks to simulate the
effects of lightning
in Earth’s early
atmosphere.
The Origin of Life on Earth
• Miller and Urey let the experiment run for a
week and then analyzed the material inside.
• They found that the interaction between the
electric arc and the simulated atmosphere had
produced many organic molecules from the raw
material of the experiment, including such as
amino acids (building blocks of proteins).
• Recently re-analysed, the original apparatus
produced more than ~20 amino acids that are in
use by life on Earth.
78
The Origin of Life on Earth
• When the experiment was run again using
different energy sources – such as hot
silica to represent molten lava spilling into
the ocean – similar molecules were
produced.
• UV radiation present in sunlight was sufficient
to produce complex organic molecules.
79
The Origin of Life on Earth
• According to updated models of the
formation of the solar system and Earth,
Earth’s early atmosphere probably
consisted of CO2, nitrogen, and water
vapour – instead of the mix of hydrogen,
ammonia, and methane assumed by both
Oparin, Miller, Urey, and Haldane.
80
The Origin of Life on Earth
• When gases corresponding to the newer
understanding of the early Earth
atmosphere are processed in a Miller
apparatus, lesser but still significant
numbers of organic molecules are created.
81
The Origin of Life on Earth
• The Miller experiment is important
because it shows that complex organic
molecules form naturally in a wide variety
of circumstances.
• Lightning, sunlight, and hot lava pouring into
the oceans are just some of the energy
sources that naturally rearrange simple
common molecules into the complex
molecules that make life possible.
82
The Origin of Life on Earth
• amino acids in the primordial soup can link
together to form proteins by joining ends
and releasing a water molecule.
The Origin of Life on Earth
• Charles Darwin thought that this must have
occurred in sun-warmed, shallow tidal pools,
where organic molecules were concentrated
by evaporation.
• It is now believed that the early linkage of
complex molecules more likely took place on the
ocean floor – perhaps near the hot springs at midocean ridges.
84
The Origin of Life on Earth
• These complex organic molecules were still not
living things. Even though some proteins may
have contained hundreds of amino acids, they
did not reproduce. They linked and broke apart
at random.
• According to the hypothesis, somewhere in the
oceans, after sufficient time, a molecule formed
that could copy itself.
• At that point, the chemical evolution of molecules
became the biological evolution of living things.
85
The Origin of Life on Earth: Problem
• The weakness of the hypothesis of Earth origins of life
is that it supposedly took only 0.75 Gyr to form fully
functional, complex bacteria (called procaryots).
• This seems a relatively short time period when
compared with ~2 Gyr needed for the early cells to
make a relatively minor advance to cells with nuclear
membrane and mitochondria (called eucaryots)
• Additional ~2 Gyr were needed to evolve into multicellular life some 0.54 Gyr ago. This also seems like a
relatively simple modification compared with the
assembly of self-replicating bacteria from
organic molecules.
86
The Origin of Life on Earth
• Since every next step in the evolution took a
shorter and shorter time, the unusually quick selforganization of chemicals into a complex bacteria
seem a priori unlikely. The process itself seems
likely though – it simply could have started
outside the Earth.
• An alternative theory for the origin of life that
‘solves’ that problem holds that reproducing
molecules may have arrived here from space.
87
The Origin of Life on Earth
• Radio astronomers have found a wide variety of
organic molecules in the interstellar medium.
• Similar compounds
have been found
inside meteorites.
The Miller experiment showed how
easy it is to create organic
molecules. It is not surprising
to find them in space.
The Origin of Life on Earth
• Whether the first self-reproducing molecules
formed here on Earth or in space or on
another planet, long before the sun was
born, the important thing is that they could
have formed by natural processes.
• The first reproducing molecule surrounded
itself with a protective membrane
89
The Origin of Life on Earth
• Experiments have shown that microscopic
spheres the size of cells containing organic
molecules form relatively easily in water.
These are Oparin’s coacervates made of
lipids (constituents of fat)
• The evolution of the
cell membrane occurred
The first organisms were
single-celled
procaryotic bacteria.
The Origin of Life on Earth
• Stromatolites and other photosynthetic
organisms began adding oxygen, a product of
photosynthesis, to Earth’s early atmosphere.
The Origin of Life on Earth
• An oxygen abundance of only 0.1 percent
would have created an ozone screen –
protecting organisms from the Sun’s
ultraviolet radiation and later allowing life
to colonize the land.
92
Geologic Time
• Life has existed on Earth for at least 3.4 billion years.
• There is no evidence, though, of anything more than
simple organisms until about 540 million years ago
Geologic Time
• This sudden increase in complexity is
known as the Cambrian explosion.
• It marks the beginning of the Cambrian
period, about 550 Myr ago
• The”explosion” took only 5-10 Myr
• The best fossils come from the geographical
region of the so-called Burgess shale, which
is in Canada
94
Evolution of life
• Cambrian Explosion
of life forms is near the
top of the column.
The left-hand column
has a linear time scale.
Evolution: body segmentation scheme
The emergence of vertebrates familiar today – fishes,
amphibians, reptiles, birds, and mammals – would be
crammed into the topmost part of the chart, above the
Cambrian explosion.
Upper row – early embryonic
stages
Lower row – late stages of
Different animal embryos.
Geologic Time
• Humanoid creatures have walked the
Earth for about 3 million years.
• This is a long time by the standard of a
human lifetime, but it makes
only a narrow
red line at the very top
of the diagram.
Geologic Time
• All of recorded history would be a
microscopically thin line at the very top of
the column.
Geologic Time
• Imagine that the entire 4.6-billion-year history of
the Earth has been compressed onto a year-long
video. First signs of life would appear in March:
• Stromatolites,
• cyanobacteria
99
Geologic Time
• The slow evolution of the first simple bacterial forms
would take up the next 6-7 months.
100
Geologic Time
• Suddenly, in mid-November(!), you would
see the trilobites and other complex
organisms of the Cambrian explosion.
Geologic Time
• You would see no life of any kind on land until….
November 28. Once it appeared though, it would
diversify quickly.
102
Geologic Time
• By December 12, you would see dinosaurs walking the
continents. By the evening of Christmas Day, they would be
gone, and mammals and birds would be on the rise.
103
Geologic Time
• If you watched closely, you might see the
first humanoid forms by suppertime on
New Year’s Eve.
• By late evening, you could see humans
making the first stone tools.
• The Stone Age would last until 11:59 PM.
• The first towns and cities would then appear.
104
Geologic Time
• Suddenly, things would begin to happen at
lighting speed.
• Babylon would flourish, the Pyramids would
rise, and Troy would fall.
• The Christian era would begin 14 seconds
before the New Year.
• Rome would fall.
• The Middle Ages and the Renaissance would
flicker past.
• The American and French revolutions would
occur one second before the end of the video.
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Geologic Time
• Imagining Earth’s history as an year-long video
gives a perspective on the rise of life.
• Tremendous amounts of time were needed for the
first simple living things to evolve in the oceans.
• As life became more complex, new forms arose
more and more quickly as the hardest problems
– how to reproduce, how to take energy
efficiently from the environment, how to move
around – were solved.
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Geologic Time
• The easier problems – what to eat, where
to live, and how to raise young – were
solved in different ways by different
organisms, leading to the diversity that you
see today.
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Geologic Time
• Even intelligence – that which appears to
set humans apart from other animals –
may be a unique solution to an
evolutionary problem posed to humanity’s
ancient ancestors.
• A smart animal is better able to escape
predators, outwit its prey, and feed and
shelter itself and its offspring.
• So, under certain conditions, evolution is likely
to select for intelligence.
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