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