In the beginning
…??
Dr. Craig Benjamin
Bright Horizons 19
Big History Lecture 2

Part  A:  The  Origins  of  the
Universe
Part  B:  The  Emergence
(and  Importance!)  of
Stars  and  Galaxies
Part  C:  The  Making  of  our
Solar  System  and
Planet
Part  D:  Origins  and
EvoluJon  of  Life

Today we cross the first Five
Thresholds of complexity!
1.
The Universe [Cosmology]:
13.8 BYA
2.
The first Stars [Astronomy]:
13.6 BYA
3.
Chemical elements [Chemistry]: from 13.5 BYA
4.
Planets and our earth [Geology]:
4.5 BYA
5.
Life [Biology]:
3.8 BYA
6.
Human beings [Anthropology]: c. 200 KYA
7.
Agriculture [Archaeology]: c. 10 KYA
8.
Modern Society [History]: c. 200 Years ago!
9.
Where’s the next threshold? [Futurology] ...

‘ How  did  it  all  begin ’ ?
•   All societies have asked this question, and devised different ways of answering it with their Creation Stories
The universe and everything in it was made by Gods
The universe and everything in it was born from Nothing
The universe is Eternal

But  all  CreaJon  stories  have  to  face   the   paradox  of  beginnings:
•   Can  SOMETHING  come  from  NOTHING?
–   If  not,  where  do  gods  come  from?
•   Can  SOMETHING  be  ETERNAL?
–   If  so,  how  is  eternity  created?
•   Can  any  CreaJon  Story  solve  these  conundrums?
Modern Quantum Physics thinks it can – with
The Big Bang Theory!
Everything in the universe was created by a subatomic particle which popped into existence 13.82 billion years ago!

The  Big  Bang
Theory  emerged   from  aQempts  to   map  the  cosmos
•   19 th  century  astronomers  tried  to  measure:
–   The  Distance  to  Stars
•   Using  parallax  (to  esJmate  distances  to  nearby  stars)
•   And  variable  stars  or   ‘ Cepheids ’  (to  esJmate  distances  to  distant   stars-­‐-­‐HenrieQa  LeaviQ)
–   And  how  Stars  Move
•   Using  spectrometers  and  the   ‘ red  shiT ’  phenomenon  to  determine   if  galaxies  were  moving  towards  or  away  from  us

Using  the   ‘ Red  ShiT ’  to   understand  the  Universe  in   the  1920s,
Edwin  Hubble  Found  …
–   Most  distant  stars  and  galaxies  are   ‘ red-­‐shiTed ’  (i.e.  they   are  moving  away  from  us)
–   The  further  away  they  are,  the  faster  they  are  moving  away   from  us
–   Which  means  the  universe  is  expanding
–   Which  means  it  was  once   infinitesimally  small
•   This  is  the  FUNDAMENTAL  PIECE  OF  EVIDENCE  FOR  …
‘ BIG  BANG  COSMOLOGY
’

…
•   Before  13.82  billion  years  ago,  there  is  nothing  we  can  really  say
–   We  have  no  evidence,  and  calcula?ons  go  crazy
–   Perhaps  Time  and  Space  did  not  even  exist
•   Then,  for  reasons  we  cannot  explain
–   Something  appeared!
§   Around  13.82  billion  years  ago  a   ‘ speck ’  appeared
–   Billions  of  billions  degrees  Celsius  hot
–   Not  sure
•   What  there  was  before  the  speck
•   Why  it  appeared
•   Physicists  cannot  answer  these  quesJons  yet  (though  there  are   many  theories),  but  it  has  a  coherent  account  from  the  moment   the  speck/singularity/first  parJcle  appeared!

•   10
-­‐35
:  Cosmic  inflaJon  created  a  large  patch  of  space   filled  with  a  lumpy  quark  soup
•   Mater  and  anJmaQer  both  existed  in  a  state  of  tension
•   Four  fundamental  forces  also  appeared  at  10 -­‐35  second   aTer  the  Big  Bang:
»   Gravity   (pen  drop)
»   ElectromagneJc  (magnets)
»   Strong  force  (glues  neutrons
and  protons  together)
»   Weak  force  (radioac?ve  decay)

•   10
-11
: Matter tried to gain the upper
hand over antimatter
•   10
-5
: Protons and neutrons formed
from quarks
•   Then a period of matter/
anti-matter annihilation …

BANG !!!!!!

Where there had been nothing, now there was everything.
A whole universe -- tiny, and fantastically hot .
For an instant, it expanded faster than the speed of light.
Then it slowed down and began to cool, but it kept expanding (and it still is today).

•   The temperature within dropped enough for the first stable atoms to form
•   Prior to that, the universe was like a
‘foggy soup’
•   When atoms formed, the fog cleared and energy and light began to flow freely, releasing cosmic microwave radiation
•   Gravity then continued to amplify differences in the gasses that filled space

Crucial  Evidence:
Cosmic  Background
RadiaJon
•   If  the  universe  began  in  a   hot,  dense  state,  there   would  have  been  lots  of   radia?on   (Gamow,  Alpher  and
Hermann,  1948 )
•   There  should  be  some   trace  of  this  radiaJon   today  (5K  or  -­‐268C)
•   Sure  enough,  CBR  was   detected  in  1965,  and   confirmed  by  satellites   in  the  80s  and  90s

•   Early  universe  was  billions   and  billions  of  degrees  hot,   too  hot  for  atoms
•   ParJcle  physicists  have  tried   to  replicate  these  condiJons,   smashing  apart  atoms
•   Predicted  that  the   universe  would  be  made   of  25%  helium  and   approx.  75%  hydrogen,   which  matches  exactly   what  has  been  found   hepwww.rl.ac.uk
Particle smashing in the UK!

So  is    the ‘ Big  Bang  Theory ’  true?
•   Absolute  certainty  is  unaQainable
•   In  the  future,  parts  of  this  story  may  begin  to  look   as  strange  as  earlier  stories  look  to  us  now
•   BUT:
–   Big  Bang  Cosmology  fits  a  huge  amount  of  data
–   Big  Bang  Cosmology,  unlike  all  earlier  creaJon   stories,  is  accepted  globally,  by  scienJsts  of  all   cultures
–   Big  Bang  Cosmology  is  by  far  the  best  ‘CreaJon
Myth’  available  if  you  happen  to  live  in  the  21 st   century!

B.  The  Emergence  (and
Importance )  of  Stars  and  Galaxies
•   From  SIMPLICITY  to  COMPLEXITY
–   The  early  universe  was   SIMPLE
–   Gradually,   COMPLEX  en??es
appeared
–   Beginning  with  stars  and
galaxies
•   INCREASING  COMPLEXITY
is  a  central  theme  of  big  history
•   How  did  the  universe  make  stars?

•   Energy:  e.g.
–   Cosmic  background  radia?on
–   Gravity
•   MaQer:
–   Huge  clouds  of
•   Hydrogen  atoms  (75%)  and
•   Helium   atoms  (25%)
•   But  that  was  enough  to
make  everything  else!
Hydrogen Clouds

Take Gravity, Hydrogen and Helium, and …
•   Gravity magnified tiny differences in temperature and density
•   Making dense regions denser
•   Pulling atoms of Hydrogen and Helium into huge clouds
•   Which got more compressed
•   And heated up (like air when pumping up a tire)

A region of star formation today:
The ‘ Cone
Nebula ’
(observed by the
Hubble Space
Telescope)

When they got
HOT enough (c. 10 million degrees C) hydrogen atoms fused together with the power of millions of hydrogen bombs, releasing huge amounts of energy.

Billions of stars were formed, starting a mere 200 million years after the big bang.
They clustered together in galaxies, each containing hundreds of billions of new stars .

A Supernova in the Large Magellanic Cloud
A star starts out as a huge cloud of gas and matter, like this cloud in the Orion Nebula
The cloud collapses and heats up until a star is formed. It may shine for billions of years
Then it dies. If it ’ s big enough it will die in a huge explosion called a supernova

•   When  stars  run  out  of  hydrogen
–   Their  centers  cool  and  collapse
–   Which  raises  pressure  and  density
–   Which  generates  very  high  temperatures  again
•   If  temperatures  reach  100  million  degrees  C
–   Helium  atoms  starts  to  fuse  into  new  elements
–   When  stars  run  out  of  helium,  they  collapse  even  more   violently,  which  creates  even  higher  temperatures  …
–   In  large  stars,  a  series  of  collapses  forge  elements   such  as  oxygen,  carbon  and  nitrogen,  up  to  iron  (No.
26  on  the  Periodical  Table)

•   How  are  the  other  elements  created?
•   In   ‘ SUPERNOVAE ’
–   Huge  stars  that  explode  so  violently  that,  for  a  few  days,  a   supernova  can  outshine  a  galaxy
–   Supernovae ,  seen  from  earth,  look  like  new  stars  (like  the   star  of  Bethlehem)
–   In  just  a  few  seconds  a   supernova  can  cook  all  the  other   elements  of  the  periodic  table
–   Then  it  scaQers  them  through  that  region  of  the  Universe
–   There  was  a  supernovae  close  to  the  region  in   which  our  Solar  System  formed!

THE PERIODIC TABLE
STAGE 1: big bang
Hydrogen (1 proton) Helium (2 protons)
STAGE 2: fusion
Iron (26 protons)
Uranium
(92 protons)
STAGE 3: supernovae create all the rest!
Gold (79 protons)

So  stars  made  the  materials  of  our   world  &  spread  them  through  the   galaxy
Gold
Iron +
Oxygen
= Rust
And the materials for carbon-based life-forms such as gerbils and … US
Carbon
(diamonds)
Gold leaf covers this statue of the goddess Serket, found in the tomb of King Tutankhamun of Egypt, and the wall behind her. Gold leaf is made by hammering solid gold metal until it is very thin.
Microsoft ® Encarta ® Reference Library 2003. ©
1993-2002 Microsoft Corporation. All rights reserved.

•   Solar  systems  most   probably  form  from  a   huge  cloud  of  material   called  a  solar  nebula
•   The  sun  absorbed   about  99.9%  of  the   cloud;  the  other  0.1%   of  the  Solar  Nebula  –   orbited  the  new  sun  in   a  series  of  rings
•   The  remnant  cloud   contained  gases,  dust,   ice  (much  the  same   material  we  find  in   comets  today)
•   These  remnants   formed  the  Solar
System

Solar Nebula Formation. The Star ‘ Vega ’ surrounded by a ring of dust & gas
[Reconstruction]

•   Within  each  orbit:  EXTREME  VIOLENCE
–   Dust,  ice  and  gas  par?cles  collided
–   And  stuck  together  to  form   ‘ planetessimals ’
•   Planetessimals  (10-­‐100  km  in  diameter)
–   Grew  like  snowballs
–   Their  gravita?onal  pull  increased
–   They  aWracted  other   ‘ planetessimals ’  and  formed  …
•   Protoplanets  (100-­‐1000  km  in  diameter)
•   Eventually,  in  each  orbit,  one  large  protoplanet  absorbed   all  the  others
•   To  form  Planets!    One  to  each  orbit

The  Planets  (Earth  is  third  from     the  Sun-­‐-­‐ not  to  scale )

The formation of one planet was particularly important for the future of all of us!
(First color photo of Earth from space, appeared on the cover of Time in 1970)

Extremely hot, because of:
1.
Violent collisions with other objects
2.
Internal radioactivity
3.
Increasing internal pressure
As a result, the earth melted and liquefied through a process called differentiation
Heavier metals melted and sank to the center
Lighter metals rose to the surface to form a crust
Gases bubbled up to make the earth ’ s first atmosphere
So the earth acquired a structure

A structure that looked like this
Surface Core
Above
Surface

!
•   Things  stabilized:
–   Earth  cooled,  so
•   Water  vapor  stored  in  the  atmosphere  rained
down  in  thunderstorms  for  millions  of  years
•   Seas  were  formed
–   Meteorites  arrived  less  frequently
–   Undersea  thermal  acJvity  pushed  conJnental  crust  around   so  that  the  surface  of  the  earth  constantly  changed.  The   theory  of  plate  tectonics  explains:
–   How  mountains  are  created
–   Why  volcanoes  and  earthquakes  occur
–   How  the  conJnents  acquired  their  posiJons
–   The  shape  of  the  modern  world

Face  of  the  Earth  180  MYS  Ago:
Pangaea:  the  super-­‐conJnent
Jurassic (Dinosaurs, 1 st birds)
North
America

Face  of  the  Earth  120  MYS  Ago
Pangaea  starts  to  break  up
Cretaceous (1 st flowering plants, marsupials)
LAURASIA
North
America
GONDWANALAND

Cretaceous asteroid impact
(dinosaurs vanish, mammals flourish)
North
America
Asteroid impact
Watch India

Humans flourish
India has collided, creating the Himalaya!
North
America

Standing at 5,500 meters on the summit of Gokyo Ri in the Nepalese
Himalayas, close to the highest point on Planet Earth (above my left hand)!

•   The  core  ideas  of  modern  Astronomy:
–   Explaining  the  Universe
•   The  core  ideas  of  modern  Earth  Sciences
(Geology):
–   Explaining  our  Earth
•   NOW:  The  core  ideas  of
modern  Life  Sciences  (Biology):
–   Explaining  Life!

All  living  organisms  share  3  key  features
1.
AdaptaJon
–   Species  of  living  things  slowly  change  &  find  new  ways  of   extrac?ng  energy  from  their  surroundings
2.
ReproducJon
–   Living  things  preserve  adapta?ons  by  replica?ng  them
3.
Metabolism
–   Living  things  find  the  energy  needed  to  support  complex   adapta?ons

Adapta?on
,  preserved  by
Reproduc?on
,  powered  by
Metabolism ,   explains  why  flies  are   more  complex  than  stars
Life introduces a new level of complexity

Remember our eight major thresholds of complexity?
1.
The Universe [Cosmology]:
13.8 BYA
2.
The first Stars [Astronomy]:
13.6 BYA
3.
Chemical elements [Chemistry]: from 13.5 BYA
4.
Planets and our earth [Geology]:
4.5 BYA
5.
Life [Biology]:
3.8 BYA
6.
Human beings [Anthropology]: c. 200 KYA
7.
Agriculture [Archaeology]: c. 10 KYA
8.
Modern Society [History]: c. 200 Years ago!
9.
Where’s the next threshold? [Futurology] ...

Biology’s  biggest  challenge  has  been   explaining  how  life   adapts
How do living organisms ‘ adapt ’ to their environment ?
The human eye is exquisitely ‘ adapted ’ for seeing
How did it get that way ?

•   Linnaeus:  Founder  of
‘ taxonomy ’
–   Life  is  fixed :  God  made  creatures   already   ‘ adapted ’ ,  and  they  haven ’ t   changed  since
•   This is the traditional answer:
–   animals are ‘ well adapted ’ because they are designed by a benign Creator
•   But, there were problems with this theory …
Linnaeus
(1707-78)

ay
Fossilized leaves
Trilobites: 200 Mill. Ys. old .

Breeders  know  that  living   organisms  can  change  through   arJficial  selecJon   e.g. modern breeds of dogs are all descended from wolves

Charles  Darwin  (1809-­‐1882):
Modern  Theory  of  EvoluJon
Twenty  years  a^er  a  voyage  round  the  world  he   reluctantly  published  his  extraordinary  theory  in  …
The Origin of Species by Natural Selection, published in 1859

Darwin  was  inspired  by  what  he   saw  on  the  Galapagos  Islands
14 nearly identical species of finches, but their beaks and heads were all slightly different
Why were the beaks and heads so different?
Was it a form of adaptation

•   Trees  on  the  Galapagos  islands   varied  slightly
•   On  each  island  finches ’  beaks  were   perfectly  adapted  to  the  local  trees   and  nuts
•
•   So  each  species  had  made  Jny
‘ adaptaJons ’  to  the  local   environment
HOW?   Galapagos Cactus
Finch

‘
’
•   Darwin  concluded  that  he  was  seeing  the  first  stages   in  the  creaJon  of  new  species
–   Tiny  variaJons  between  individuals  get  magnified  when   geographical  barriers  (such  as  canyons  or  seas)  stop   individuals  of  the  same  species  from  maJng
–   Over  Jme,  groups  separated  geographically  diverge  more   and  more  from  each  other
•   Eventually,  when  the  groups  can  no  longer  interbreed,   they  form  new  species
•   This  is  the  CORE  IDEA  of  modern   biology  –  evoluJon  by   ‘ Natural
SelecJon ’

•   The  environment  constantly  changes
–   So  the  definiJon  of   ‘ fitness ’  constantly  changes
–   So   ‘ natural  selecJon ’  is  an  endless  process
•   This  explains  the  huge
variety  of  organisms
that  have  inhabited
our  earth
•   Natural  SelecJon  is  the
source  of   the rich biodiversity on  earth!

ImplicaJons  of   ‘ Natural  SelecJon ’
1.
Blind processes can create things as complex as living organisms
2.      All  living  creatures  are  related
–   This  means  that  all  living  creatures  share  the   same  ancient  ancestors
3. Humans are closely
related to apes
–   So humans and apes share common ancestors quite recently (in biological terms)

’
•   Fossils
•   SimilariJes  between   species  (embryos)
•   Geographical   distribuJon  of  species   www.micromacro.co.uk/

•   We  can  see  evoluJon  at   work  (fruit  fly,  HIV,  other   viruses)
•   We  know  how  heredity   works  ( DNA )
•   We  can  show  geneJcally   that  all  living  organisms   are  related
•   Mitochondrial  DNA   shows  that  all  human   females  are  descended   from  a  common  ‘mother’

•   Darwin ’ s  theory  of   evoluJon  is  now  the  core   idea  of  modern  Biology
–   As  fundamental  as   ‘ Big  Bang
Cosmology ’  is  in  Astronomy
–   Or   ‘ Plate  Tectonics ’  in  Earth
Sciences
But one big question remained for biologists to address …
How did life appear in the first place?
pharyngula.org/ index/weblog/2004/02/

1.
The  Earth  made  simple  organic  molecules
(amino  acids,  nucleoJdes,  phospholipids  in   fats,  etc.)
2.
These  turned  into  organic  chemicals  that   evolved  and  behaved  a  bit  like  living   organisms  (chemical  evoluJon)
3.
DNA  emerged  to  control  replicaJon
(the  geneJc  code)

Making  Simple  Organic  Molecules:
The  Urey-­‐Miller  Experiment
•   Create  a  model  of  the  early  atmosphere  in  a  flask
•   Energize  it  with  heat  and  electric  sparks,  and  wait:
•   Within  7  days:
–   a  dark  red  sludge  appears,  containing  many  elements  from   which  life  is  made:
•   Amino  acids  (from  which  proteins  are  made)
•   NucleoJdes  (from  which  DNA  is  made)
•   Phospholipids  (from  which  cell  membranes  are  made)
•   So:  making  the  raw  materials  of  life  is  easy!

Making  More  Complex  Organic
Chemicals:   ‘ Chemical  EvoluJon ’
•   Under  the  right  condiJons
–   Organic  chemicals  link  into  huge  chains  of  millions  of   atoms  to  form  proteins  and  nucleoJdes
Amino acids are simple
Proteins are made from chains of amino acids
Proteins fold up into complicated balls of matter

Where  were  condiJons  right  for  this   to  have  first  taken  place?
Near  deep-­‐sea  volcanoes
Chains of deep-sea volcanoes
•   CondiJons  were  ideal:
–   No  ultraviolet  rays
–   No  meteorite  collisions
–   Heat  from  the  earth ’ s   core
–   Plenty  of  water
–   Plenty  of  chemicals
•   Here  is  where  the  first   life  probably  formed!

•   Now  we  have  complex  organic  chemicals
–   Made  from  the  same  stuff  as  living  organisms
–   With  metabolism  (taking  in  energy)
–   Capable  of   ‘ adapJng ’  (chemical  evoluJon)
–   They  can  even  reproduce  in  a  fashion
•   But
–   They  reproduce   inaccurately ,  so  they  cannot  preserve   complexity  over  many  generaJons
–   The  key  to  life  is  more   accurate  reproducJon
•   How  do  you  precisely  reproduce  something  with   billions  of  carefully  arranged  molecules?

The  GeneJc
Code!
•   DNA:  the  molecule  of  life
•   How  does  it  work?
–   If  organisms  reproduce   too   perfectly ,  adapta?on  and   change  are  impossible
–   If  they  reproduce   too   imperfectly ,  they  cannot   retain  the  informa?on   needed  to  construct  viable   organisms
•   DNA  achieves  a  perfect   balance:
–   Accurate   copying
–   With  just  a  dash  of   variaJon
–   This  is  the  key  to   biodiversity

Finally, a brief history of life on
Earth: Tale of increasing complexity
8 stages in the history of life on earth
1. First organisms
2. Photosynthesis
3. Prokaryotes à Eukaryotes
4. Sexual reproduction
5. Multi-celled organisms
6. Living on the land
7. Vertebrates
8. Mammals

1.  The  earliest  living  organisms  on   earth  were  ...
•   Prokaryotes
–   Too  small  to   be  seen  with   the  naked  eye
–   No  nucleus:   genes  float   freely  inside
DNA but no nucleus

•   Some  organisms  rose   to  the  surface  of  the   seas
•   And  learnt  to  extract   the  energy  of
sunlight  through
PHOTOSYNTHESIS
(like  plants  today)

Why plants are green
Chlorophyll is green, and is present in all plants
Chlorophyll molecules are where photosynthesis occurs

‘
’
‘
’
•   The  oxygen  produced  by  photosynthesizers  was   poisonous  for  most  species
•   But  eventually,  some  bacteria  learnt  to  exploit   the  excepJonal  chemical  energy  of  oxygen
•   Those  that  could  use  oxygen  flourished  and   became  more  complex:
•   The  first   ‘ eukaryotes ’
–   They  used  the  energy  from  oxygen  and/or  sunlight
–   Their  genes  were  protected  inside  the  nucleus
–   They  were  much  larger  and  more  complex  than  prokaryotes

Eukaryotes (10 – 100 times as large as prokaryotes )
The nucleus protects the cell ’ s DNA
Mitochondria generate energy from oxygen

What was bacterial sex like?
•   For  most  prokaryotes  it  was  boring:  they  just  cloned
•   But  some  eukaryotes  began  to  swap  genes  before   reproducing.    Result?
–   Their  offspring  were  more   varied
–   Greater  variety   accelerated  the  pace  of  evolu?onary  change

Tube sponges may be similar to the earliest multi-cellular organisms
•   For  c.  3  billion  years,  all  life  on  earth   consisted  of  single-­‐celled  organisms
•   From  c.  600  million  years  ago:
–   Some  cells  gathered  together  in
‘ socieJes ’  (like  sponges)
–   Some  cells   specialized ,  and  became  more   dependent  on  their  neighbors
–   Some  became  so  dependent  on  other  cells   they  turned  into  large,  single  organisms

The first vertebrates probably looked like
‘ lancelets ’ .
They are extremely simple fish, with no heart and no brain!

7.  1st  large  organisms  to  survive  on   land:  from  c.  370  million  years  ago
•   Surviving  away  from  water  was  tough
–   Supplies  of  water  had  to  be  found
–   Skins  needed  to  prevent  excessive  dryness
–   Eggs  and  offspring  needed  to  be  protected
•   Which  large  species  got  there  first?
–   Plants  were  probably  first,  more  than  400  million   years  ago
–   Followed  by  insects
–   Then  the  first  land  animals,
early  forms  of  amphibians,
c.  370  million  years  ago   Ichthyostega lived about 370 million years ago

•   Mammals  were
–   Warm-­‐blooded
–   Fed  their  young  with  milk
–   Had  fur
•   The  first  mammals  were  small,
shrew-­‐like  creatures  living  in  a
world  dominated  by  dinosaurs
Morganucodon lived c. 250 million years ago.
It was the size of a small mouse or shrew
st

65 million years ago, a giant meteor came crashing down to earth, and the dinosaurs were no more.
This allowed mammals to prosper and evolve!!

Primates  lived  in  trees.
To  survive  in  trees  they   needed:
•   3D  vision  and
•   large  brains  to  process  visual   informaJon
•   And  hands  that  could  grip   with  precision
Imagine  living  in  a  tree   without  these  abiliJes:   you ’ d  fall  out!

According  to  all  the  available   scienJfic  evidence  we  are  descended   from  primates!
Bonobo chimps – our very close relatives (98.4% of our DNA is identical to that of chimps)
All chimps, apes and hominines
(including humans) are descended from a common ancestor who lived 8 MYA

•   In  this  lecture  we  have  covered  almost    13.8  billion   years  of  history,  and  now  the  bizarre  species  of  homo   sapiens  is  poised  to  join  the  modern  creaJon  myth!
•
actually  be  very  difficult  because  of  the  incredible   complexity  of  human  socieJes!
•   Next  Jme  we  bring  our  story  closer  to  the  present
•   Before  taking  it  hundreds,  thousands,  and   even  billions  of  years  into  the  future  in  our