Planets & Life
Planets & Life
PHYS 214
PHYS 214
Dr Rob Thacker
Dr Rob Thacker
Dept of Physics (308A)
Dept of Physics (308A)
thacker@
astro.queensu.ca
thacker@
astro.queensu.ca
Please start all class related emails with
Please start all class related emails with ““214:
214:””
Today
Today’’ s Lecture
s Lecture
��Evolution of the cell
Evolution of the cell
��Possibility of
Possibility of panspermia
panspermia
��Brief m
ention of Earth geological history (we
Brief m
ention of Earth geological history (we ’’ll talk
ll talk
more about this later)
more about this later)
��Prokaryotic cell, eukaryotic cell
Prokaryotic cell, eukaryotic cell
Tim
eline of Earth H
istory
Tim
eline of Earth H
istory
Panspermia
Panspermia
��Some people believe that the origin of life on Earth form
Some people believe that the origin of life on Earth form
inanimate material is just too
inanimate material is just too ““impossible
impossible””
��The suggestion is that somehow life on Earth was seeded from spa
The suggestion is that somehow life on Earth was seeded from spa ce ce ––
““panspermia
panspermia””
��However, this is not a true solution to the problem posed
However, this is not a true solution to the problem posed ––
life
life
must originate from somew
here
must originate from somew
here
��Strongly advocated by the late Fred H
oyle & Chandra
Strongly advocated by the late Fred H
oyle & Chandra
Wickram
asinghe
Wickram
asinghe
��Technically the idea that life arose elsew
here and was transferr
Technically the idea that life arose elsew
here and was transferr ed
ed
to Earth is called
to Earth is called ““exogenesis
exogenesis””
��Panspermia
Panspermiais technically the idea that life (anyw
here) is seeded from
is technically the idea that life (anyw
here) is seeded from
space itself
space itself
��Note that
Note that panspermia
panspermiais also discussed in terms of supplying
is also discussed in terms of supplying
molecules that m
ay have been necessary to produce life, rather
molecules that m
ay have been necessary to produce life, rather
than say depositing spores
than say depositing spores
Material
Material does
does
transfer between
transfer between
planets
planets
�We do know that a “significant”am
ount of
material from M
ars has reached Earth
�Thus far 34 m
eteorites have been identified
has having come from M
ars
�We also have around 40 meteorites which
are known to have come from the Moon
�We can identify these objects as coming
from M
ars firstly by their young age (using
radiometric dating) –norm
al m
eteorites
were form
ed at the beginning of the solar
system
�
Then apply a process of elimination
�Venus’s atmosphere and lack of cratering
suggests it is a very unlikely source
�Moon possible, but we know a lot about its
composition which we can use
�The main source of energy to project these
meteorites from M
ars must be impact
events
�Very large ones m
ight sm
oothly accelerate
material to high velocities…
Could very
hardy organic m
aterial survive in deep space
for long enough?
Starting point for cell
Starting point for cell ““evolution
evolution””
��Primordial E
arth has reached the point where
Primordial E
arth has reached the point where
water is freely available
water is freely available
��Could either have been by minerals that release
Could either have been by minerals that release
water or by
water or by resupply
resupplyby comets
by comets
��Atm
osphere contains most CO
Atm
osphere contains most CO
22, N, N
22, w
ith some
, with some
CO and H
CO and H
22OO
��Only trace amounts of oxygen
Only trace amounts of oxygen
��Probably still a very high flux of UV radiation from
Probably still a very high flux of UV radiation from
the Sun
the Sun
Relative sizes of organic
Relative sizes of organic ““building
building
blocks
blocks ””
Form
ation of the DNA molecule
Form
ation of the DNA molecule
��The Miller
The Miller-- U
rey
Ureyexperiment shows we can synthesize am
ino
experiment shows we can synthesize am
ino
acids easily
acids easily
��The
The ““distance
distance””between simple amino acids and D
NA is vast
between simple amino acids and D
NA is vast
though
though
��DNA replication in itself is complex, involving enzymes (protein
DNA replication in itself is complex, involving enzymes (proteins) &
s) &
RNA
RNA
��Presents a
Presents a ‘‘chicken and egg
chicken and egg’’problem: the enzymes are needed to create
problem: the enzymes are needed to create
the DNA, yet the enzymes cannot be reproduced without the inform
the DNA, yet the enzymes cannot be reproduced without the inform
ation
ation
supplied by the am
ino acids
supplied by the am
ino acids
��RNA though is simpler, and also appears unique in that
RNA though is simpler, and also appears unique in that
��RNA can code for genetic inform
ation
RNA can code for genetic inform
ation
��Certain form
s of RNA are self catalyzing
Certain form
s of RNA are self catalyzing
��Could RNA actually have initially been the initial seed for the
Could RNA actually have initially been the initial seed for the
development of DNA?
development of DNA?
��Did life begin with RNA based organisms and evolve DNA later?
Did life begin with RNA based organisms and evolve DNA later? ““RNA
RNA
world
world””hypothesis
hypothesis
Form
ing complex molecules
Form
ing complex molecules
��Given appropriate groups in a m
onomer,
Given appropriate groups in a m
onomer,
polymerization can occur with the release of water
polymerization can occur with the release of water
��Hydroxyl groups, or a combination of carboxyl and amine
Hydroxyl groups, or a combination of carboxyl and amine
groups for exam
ple
groups for exam
ple
��The new
ly bonded systems retain the capability for further
The new
ly bonded systems retain the capability for further
polymerization
polymerization
��The primary issue here is that water m
akes
The primary issue here is that water m
akes
polymerization difficult
polymerization difficult
��Breaks down polymers rather than building them
up
Breaks down polymers rather than building them
up
Creating something like a cell
Creating something like a cell
wall/mem
brane
wall/mem
brane
�Amphiphilicmolecules have
a hydrophillichead &
hydrophobic tail
�In presence of water they
form
monolayersas the
hydrophilic heads try to sit
on the surface of the water
�Under disturbances the layers
can form
“micells”sm
all
spherical regions with
hydrophilic surfaces
�Double layers can combine
to enclose trapped regions of
water “bilayervesicle”
Microspheres
Microspheres
�In 1958, Stanley Fox created
“proteinoids”
by heating dry amino
acids
�After dissolving these new
molecules in water the proteinoids
form
ed small spheres about 2 m in
diameter –microspheres
�The microspheres
mimicked
biological m
embranes in that they
could shrink or sw
ell depending
upon the surrounding salinity
�Amphillicmolecules also m
ay have
been deposited on Earth by
meteorites
�Compounds on the Murchison
meteorite dem
onstrate this
behaviour
Role of minerals?
Role of minerals?
��Minerals (
Minerals ( ““clays
clays ””) have frequently been cited as playing
) have frequently been cited as playing
an im
portant role in the development of complex
an im
portant role in the development of complex
organic polymers
organic polymers
��Protection
Protection: small air pockets can be filled by organic m
aterial
: small air pockets can be filled by organic m
aterial
and then sheltered
and then sheltered
��Support
Support: by providing a structure on which to accumulate
: by providing a structure on which to accumulate
and interact (am
ino acids concentrate on surfaces)
and interact (am
ino acids concentrate on surfaces)
��Selectivity
Selectivity: different crystal structures exhibit different
: different crystal structures exhibit different
chirality
chiralityand this m
ay have played a role in selecting the left
and this m
ay have played a role in selecting the left--
handed m
olecules on which life is based
handed m
olecules on which life is based
��Catalysts
Catalysts : N
itrogen is required in a form
other than N
2 : N
itrogen is required in a form
other than N
2 ––
possible that iron oxide near vents of N
possible that iron oxide near vents of N
22and H
and H
22allowed the
allowed the
production of biological useful NH
production of biological useful NH
33
Cells
Cells
��Cells
Cells are the basic units of organisms
are the basic units of organisms
��Studies of
Studies of cell division
cell divisionshowed that genetic inform
ation is
showed that genetic inform
ation is
carried in the
carried in the chromosomes
chromosomes, found in the cell
, found in the cell nucleus (
nucleus ( at least
at least
for eukaryotic cells
for eukaryotic cells).
). A chromosome is a very long, continuous
A chromosome is a very long, continuous
strand of DNA
strand of DNA
��Human cells have 46 chromosomes (23
Human cells have 46 chromosomes (23 pairs
pairs , one of each pair from
, one of each pair from
mother, one from father)
mother, one from father)
��Bacteria typically have a single chromosome tethered to the mem
bBacteria typically have a single chromosome tethered to the mem
brane of
rane of
the bacteria
the bacteria
��In turn, chromosomes are composed of
In turn, chromosomes are composed of genes
genes; a gene is a
; a gene is a
sequence of DNA that encodes a protein (
sequence of DNA that encodes a protein (one gene
one genefor
for each
each
protein
protein); rem
ember the
); rem
ember the genetic code
genetic codediscussed earlier, with
discussed earlier, with
each
each codon
codon(triplet of DNA base
(triplet of DNA base --pairs) encoding one
pairs) encoding one amino
amino
acid
acid. One (human) chromosome contains several thousand
. One (human) chromosome contains several thousand
genes
genes
Mitosis:cell divides to give two cells with the same genetic
inform
ationas parent cell
--in human bodies (eukaryotic cells), this is cell replication
--in single-celled organisms, this is reproduction
Mitosis
Mitosis movie
Meiosis: responsible for creating gametes
(sperm or egg).
--One cell divides to form
4 gam
etes with halfthe genetic
inform
ation (chromosomes) in each gamete.
--gametes are not identicalto parent cell
Meiosis
Meiosis movie
●Meiosis: responsible for creating gametes
(sperm or egg). One
cell divides to form
4 gam
etes with halfthe genetic inform
ation
(chromosomes) in each gam
ete
--in sexual reproduction, sperm and egg join to create a whole
set of chromosomes
--each gam
ete ends up with one chromosomefrom each
homologous pair, i.e. one chromosome from each parent. This
happens at random
--this explains Mendel's results for dominant and recessive
genes and heredity
●So chromosomes
carry the genetic inform
ation (genes),
specificially via DNA
--Eukarya: plants, animals
--Bacteria: simple, old organisms
--Archaea: now recognized to be a new
domain
Domains of Life
Prokaryotic Cell
(Bacillus megaterium)
Prokaryotes
Prokaryotes
��Includes bacteria
and archaea, the oldestlife on the planet
�Despite the inherent “difficulty”
in form
ing DNA, bacterial life appeared
on the planet at least 3.5 Gyrago
�No separate nucleus; their DNA (in a single, long strand, w
ith
several thousand genes) is dispersed in the cell
�They don't have complicated internal structure of eukaryotic
cells. But they do have DNA/RNA, and m
ake their own
proteins
Bacteria: simple-celled organisms (e.g. blue-green algae,
stromatolites) Fossilized rem
ains of bacteria date to 3.5
Gyrago
Stromatolites–fossil remains of early
bacteria are very similar
Archaea: similar to Bacteria, but now considered a
separate “domain”of life
--distinction from bacteria is partially based on a chem
ically distinct cell w
all
--were initially categorized as a subclass of bacteria
●Archaea include many extrem
ophiles
●Archaea
are simple, thought to be first life
to have arisen on Earth,
when there was little/no oxygen
●Later they adopted photosynthesisto use Sun's energy. Earliest
cells m
ay have used H
2S instead of H
2O, freeing S instead of O
2
●Photosynthesis releases oxygen
, building up atm
osphere to present
levels. This would have been deadly to (some/most) early Archaea
(but not all). Archaea would have been present during transitionto
an oxygen-based atm
osphere.
Changes in Earth
Changes in Earth’’ s atm
osphere
s atm
osphere
�The absence of oxygen forced early
life to be completely anaerobic
�However, the geological record
shows massive amounts of iron
oxides (“banded iron
form
ations”=BIF) deposited
around 2.7 G
yrago
�Cyanobacteriawere the first
organisms to develop
photosynthesis and release oxygen
into the atmosphere
�Believed that dissolved iron in the
Earth’s ocean reacted with the new
oxygen at the surface
�Huge deposits m
ay possibly be
related to snowball-Earth events
Eukaryotes
�Around when oxygen was becoming im
portant
(2-2.5 bya), eukaryotes arose to take advantage
of it (~2.7 bya)
�Eukaryotes keep their DNA inside a central
nucleus. They also have a lot more D
NA than
bacteria, and m
ore complicated structure (e.g.
sub-structures like mitochondria or chloroplasts)
within “organelles”
Eukaryotic Anim
al Cell
Eukaryotic Plant Cell
●Seem
s that eukaryotesarose from
prokaryoteswhich developed sym
biotic
relationships, eventually residing within
same cell mem
brane and specializing
functions
--e.g. chloroplasts/mitochondria with own
gene system
s
●Eventually cells form
ed relationships with
other cells, producing multi-cellular
organisms. A human has ~10
13cells
cooperating together!
Reproduction:
●Asexual: prokaryotes and eukaryotes can
reproduce asexually, creating identical copies
(mitosis)
●Sexual: only in eukaryotic cells; results in
new
combinations of genes at each
generation & m
ore rapid evolution (meiosis)
Cambrian Explosion
Cambrian Explosion
��For billions of years, life on Earth consisted only of single
For billions of years, life on Earth consisted only of single --cell organisms,
cell organisms,
from which primitive multi
from which primitive multi --celled creatures developed (e.g. trilobites), and
celled creatures developed (e.g. trilobites), and
then later soft
then later soft-- bodied organisms like jellyfish
bodied organisms like jellyfish
��But ~600 million years ago, there was an
But ~600 million years ago, there was an explosion
explosionof large numbers of
of large numbers of
complex creatures: the Cam
brian Explosion.
complex creatures: the Cam
brian Explosion.
��Not sure why it happened: m
ore oxygen available, nutrients, ris
Not sure why it happened: m
ore oxygen available, nutrients, rise of predators
e of predators
(( ““arms race
arms race””))
��This event has great significance in evolutionary theory, m
any d
This event has great significance in evolutionary theory, m
any different phyla
ifferent phyla
(( ““body designs
body designs ””) arose, but there were remarkably few
species
) arose, but there were remarkably few
species
��No new
phyla have been created since!
No new
phyla have been created since!
��Nothing like it has been seen since
Nothing like it has been seen since
--only bacteria/archaea until
summer
--oxygen-rich atm
osphere through
summer, but Cam
brian
explosion doesn't happen till N
ov
13!
--Dinosaurs: D
ec 13-26
--First humans: 6 pm D
ec 31
--Technological society: 11:59:59.9
pm D
ec 31!
●Life may take billionsof years to
achieve intelligence (and only a
short window to m
ake contact).
Life on Earth compressed into one
Life on Earth compressed into one
year
year
Summary of lecture 20
Summary of lecture 20
��We have plausible arguments for how D
NA m
ay have
We have plausible arguments for how D
NA m
ay have
arisen, but many key issues are m
issing
arisen, but many key issues are m
issing
��RNA m
ay be the key
RNA m
ay be the key
��Potentially self catalyzing
Potentially self catalyzing
��Can carry inform
ation necessary for reproduction
Can carry inform
ation necessary for reproduction
��Early life relied upon the prokaryotic cell
Early life relied upon the prokaryotic cell
��The evolution of the complex eukaryotic cell is widely
The evolution of the complex eukaryotic cell is widely
believed to be due to the rise of symbiotic relationships
believed to be due to the rise of symbiotic relationships
between smaller and larger prokaryotic cells
between smaller and larger prokaryotic cells
��Complex animal life appears only 500 m
illion years ago,
Complex animal life appears only 500 m
illion years ago,
even though the first bacteria appear 3,500 million years
even though the first bacteria appear 3,500 million years
ago
ago
Next lecture
Next lecture
��Guest lecture next Friday (8
Guest lecture next Friday (8ththMarch) by Dr Virginia
March) by Dr Virginia
Walker (Biology) on
Walker (Biology) on extremophiles
extrem
ophiles