BAEZ, John, Life's Struggle to Survive , SETI, UC Riverside, Dec 17 2013

this is at the SETI Institute in Mountain View at noon on
Tuesday  Dec 17 2013

John's title today is Life's Struggle to Survive;

about 40 billion earthlike planets in our galaxy. (estimate from Kepler)

but what fraction of Earth-like planets have civilizations we might detect?

he will talk about some obstacles that life on OUR planet had to overcome to reach the point where other civs can detect us.

Holocene means the present  we just entered the
Anthropocene (human influenced Earth)
huge human-induced influence...
(he recounts the extent of human induced influence in the next few slides)

rate of species going extinct is 100 to 1000X  the usual bkgrnd rate...

(his slides AREonline, along with  literature citations)  qv.

pop. of large ocean fish have decline by 90% since 1950...

ones we do not eat are soaring (like jellyfish)

about 25% of all chemical energy produced by [plants is now used by humans

Humans now take more N2 from atmosphere and convert it into nitrates than all other processes combined!
(some plants do it  (like legumes)

8 to 9X as much phosphorus is flowing into oceans than the natural bkgrnd rate...

both N2 and PO4 flowing into oceans  causing algal blooms and have
creagted 400 dead zones from 1 to 70K km2 in area...

gulf of Mexico at Mississippi where outflow is...
only jellyfish survive cuz of pollution induced dead zone.

C02 variations...  now over 400 ppmv.

exceeding all levels in past 400,000 years.  see his graph

CO2 is shooting up vertically since 1800 
 (it was at < 200 and has doubled in 300 years)

the last peak at about 280  around 100K years ago.

reconstruction of temp from 73 difft records  from Marcott et al.
big spike at present...

we were heading toward another ice age but we reversed  it...

graph of Arctic sea ice

minimum 1 day area in million km2... it has dropped by 50% in the past few years....

We are locked in a Tragedy of the Commons or Prisoners dilemma...

cows on the Commons...  (needs to a global limit on Cows on the Commons but
it is to the benefit of each rancher to put another cow onto the commons)

Prisoners Dilemma:  each of two can rat on the other...
(we'll give you a short sentence if you rat out the other one)

UN climate change negotiations,  there is NO question of the
reality and importanc eof human-caused climate change.
No one questions it!!!  (there are no disbeleivers)...
the only Q is what to do about it and who should do it.
That's why negot. fail.

but some coutnries are going ahead and restraining CO2 anyway.

How bad will it get?

it seems unlikely that life on Earth or even our species wil go extinct but
out popul. could get knocked down.

Sherwood and Huber....

they argue that  at 35 degr C  extended... will induce hyperthermia in humans and mammals and dissip of metab heat would be impossible.

it would begin to occur with global mean warmingof abt 7 degr C.

event warming of 12 degr C is possibe from fossil fuel burning.

could we ever let thins get that bad?
maybe.
an intergenerational arms race  (to keep the economy going)
with each generation saying it urgently needs to burn fossil fules cuz situation is so desperate.

it IS possible.

sometime btwn  3.5 and 2.6 billion yuears  ...
the first photosynth organisms dumped deadly gas into atmosphere... Oxygen!

he shows banded iron formation form 2.1 B years ago...
(disaster for anerobic orgs)
banded iron:  layers  of  black vs red stuff  (falling to the sea bed)

first O2 got sucked up by oxidizable material  (eg by dissovled iron and organic matter)

The O2 catastrophe...

but luckily it happened slowly enuf that evolution saved the day...

but then as O2 entered atmos.  methane  was eliminated...

Faint young sun paradox... (sun was weaker)  perhaqps Methane was needed (potent greenhouse gas)
to warm the Earth.

eliminat of Methane may have caused the most severe ice age in hx... the Huronian glaciation that last from
2.4 to 2.1 B yrs ago...

much later   brwn  800 to 625 M years ago... a series of Snowball Earth events 
(perhaps due to high albedo)  terminated by  volcanos perhaps putting out CO2.

5 really big extinctions...

graph of Genera of marine organisms....

Marine life makes the easiest fossils to find...

Big Five  mass extinction events...

from Rohde and Muller... Cycles in fossil diversity...

Permian-Triassic  was abt  250 M years ago...

here are the Big Five

Ordovician-Silurina Extinction  was  440 MYA to to 450 MYA
57% of marine genera went extinct...

what caused it?

one theory...  continent Gondwana drifted over Sout Pole

(current ice ages thot due to water circualting around Antarctica and freezing it...
cools Earth by cuzing it to freeze)

next  Late Devonian Extinction was
375 MYA  abt 50% marine genera went extinct..

70% of marine genera extinct...
reef-bilidng orgs wiped out...

shortages of O2 in ocean bottom waters...
therre were pulsesof extinction over abt 25 MYears....

3)  the biggest...  Permian-Triassic Extinction was 251 MYA
and 83% of marine genera went extinct....

were prev land dinosaurs that were wiped out....

from Micahel Benton... When Life Nearly Died... the greatest mass exctinciton of all time...
great illustrations..

?   cause:   ?  asteroid impace,  massive volcanic eruptions  that caused severe global warming and depletion of O2.

  poss cuzed by  mass release of methane from clathrates under ocean...
methane molec embedded in water cage.
a lot of carbon in atmos

4)  Triassic-Jurassic Extinction  205 MYA
48% of marine genera died out.

killed off last of large amphibians...

at this time... one supercontinent  Pangeas... split into
Laurasia and Gondwana.

5)  KT  = Creaceous-Tertiary Extinction  65 MYA
50% of marine genera extincted.

prob due to asteroid that hit  Chicxulub.
this was 10 km across and deliv  100 teraton of TNT
2M time sthe largest manmade bomb  the 57 megaton  Tsar Bomba.

(see YouTube of Tsar Bomba)

but that was nothing comapred to  Theia impact on EArth to form Moon.
Theis.. sl bigger than Mars... slowly hit Earth

see Robin Canup  simulation YouTube...
Giant Impact Hypotesis...

all Earth's crust and some mantle was melted...

within a century  it forms the Moon...

more recently  a new theory of smaller body impacting Earth headon at higher speed.

However despite the glamor,  only one mass extinction is clealry linked to an impalct.

1)  How stable is Earth's climate?

the clathrate gun hyptohesis...  says
methane locked in sea bed can escape..
reservees have 500 to 2500 billion tonnes ofr carbon... v large compared to
5000 in atmosphere.

might explain  Paleocene  PETM event....

are we now in danger of that?
good news... starting from a cold point now  but
methane already bubbling up from East Siberian Artctic Shelf  Natalia Shakhova

its abt  12 M tonnes per of cabon per year... but
that is tiny compare to 10 billion tonnes/ year put into atmos by humans...

2)  how does life respond to a tragedy of the commons

if it happens slowly the life may evolve its wayout...

it it happens fast, can intelligence figure a way out?

must be  something more than just indiv players trying to maximized their own gain!

*****************

Adrian Brown:  How abt  geoengineering strategies?

A:  we should seriously research it  (not do it)
eg  emitting sulfates in stratosphere to reflect sunlite...
most promising  (but it has problems)
but wont' solve probs of CO2 in oceans  (will still kill orgs in ocean)

comment : economic  self-itnerest  to stop burning coal, eg  nuclear  energy...

Q:  was the fact that life survived due to sheer luck?  matters  cuz
it affects Drake Equation factors  (prob of life surviving to evolve to intel.)
A  who knows

comment:  accel  weathering... eg  by devices on coal plants
being develp at LLNL  Lawr Livermore...  scrubbers...

Adrian Q abt Singapore:  Pres of Singapore inter. in nuclear energy...

Dave Ross:  even if we solve  CO2 production, we still have  expon. growth of energy utilizaiton
that independ. creates problems  (due to excess heat production)

Q abt  PETM Paleocene Eocene Thermal Maximum  when temps shot up by 6 degr C in just 20,000 years.