Life: Origin, Evolution, Extinction: The epic story of life on earth

132 Pages·2016·23.87 MB·English

by  New Scientist

VOL THR EE / ISSUE T WO
O R I G I N,
E V O L U T I O N,

E X T I N C T I O N
THE EPIC STORY OF LIFE ON EARTH
£9.99
0 2
9 772054 638003

THE COLLECTION
Life story
VOL 3 / ISSUE 2 HOWdidlifebegin?Thisisoneoftheeternal Whatdrovethisprocess?Whatwerethefirst
LIFE ON EARTH: questions.Allcultureshaveacreationstory, complexcreaturesonEarth,andwhatdrove
ORIGINS, EVOLUTION, butmodernsciencehasthebestoneofall– thesuccessiveexplosionsofevolutionary
EXTINCTION anear-completeaccountofhowourplanet creativity?
wentfromabarrenlumpofrocktoone Chapter3takesatourofthemost
coveredinarichdiversityofplants,animals fascinatingfossilseverdiscovered,including
andmicrobes. feathereddinosaursandmyriadotherlong-
NEWSCIENTIST
THECOLLECTION Foralmostabillionyearsafteritformed, deadcreatures.Whatcanwelearnaboutthe
110HighHolborn, Earthwasalifelessplacewithhellish behaviourofanimalsfromtheirfossilised
LondonWC1V6EU
[phone] conditions.Butaround3.8billionyearsago, remains,andwherecanwefind“missing
[email protected] afterthesurfacehadcooledandoceans links”thattellsusaboutkeytransitionssuch
Editor-in-chiefGrahamLawton formed,somethingamazinghappened.Out ashowbirdstookflight?
EditorAlisonGeorge ofEarth’sprimordialchemicalsaroseanentity InChapter4wetakealookatGaiatheory,
ArteditorCraigMackie
PicturesNewScientist capableofreplicatingitself.Lifewasborn.The tacklingthecontroversialquestionofwhether
picturedesk rest,astheysay,isprehistory. ourplanetactslikeagiantorganism,capable
SubeditorJuliaBrown
GraphicsDaveJohnston Theforcesofevolutionworkedonthis ofregulatingitsownenvironment.
ProductioneditorMickO’Hare simplelifeformanditsdescendantstocreate Chapter5isallabouttheunifyingtheory
ProjectmanagerHenryGomm
PublisherJohnMacFarlane allmannerofusefuladaptationsincludinga oflife.Althoughthebeautifulandsimple
systemtocaptureenergyfromthesun ideaofevolutionbynaturalselectionwas
©2016ReedBusiness
InformationLtd,England (photosynthesis),biologicalcomputers firstput forward in 1858, many myths and
NewScientistTheCollectionis (brains)andevenabiologicalwheel. misconceptions about it still persist. We tackle
publishedfourtimesperyearby
ReedBusinessInformationLtd Wewillprobablyneverknowexactlyhow them head on.
ISSN2054-6386 thisfirstlifearoseorwhatitwaslike,butthere Where there’s life, there’s death. This is the
PrintedinEnglandbyPrecision aremanyothermysterieswecanhopeto appropriate subject of our final chapter:
ColourPrinting,Telford, solve.ThisissueofNewScientist:The extinction. The fossil record reveals that most
Shropshire,anddistributedby
MarketforceUKLtd Collectiontacklesthesequestions.Ittellsthe species that existed have gone. Why? What
[phone] epicstoryoftheonlylivingplanetweknowof were the biggest mass extinctions? And what
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[phone] intheuniverse,fromlife’soriginstothe would our planet look like if all life suddenly
[email protected] watershedmomentsinitshistory. died?
Chapter1isaboutthedawnoflife.Charles Prepare to go on a journey of a lifetime.
Cover image Darwinimaginedthatlifearosein“some
Aixsponza
warmlittlepond”,buttherearemanyother Alison George, Editor
possiblecradlesoflife.Whereandwhendidit
happen?Whatingredientswereneeded,and
was the event inevitable?
Chapter 2 explores the key steps in the early
development of life. For the first 1.5 million
years of its existence, life consisted of simple
microbes, but then things got more
interesting. Cells developed internal “organs”
and multicellular life eventually followed.
Life on Earth: Origins, Evolution, Extinction | NewScientist: The Collection | 1
CONTENTS
THE COLLECTION 2
CONTRIBUTORS VOL3/ISSUE2
ColinBarras
isawriterinAnnArbor,Michigan LIFEONEARTH:
StephenBattersby
isaconsultantforNewScientist
ORIGINS,
MichaelJ.Benton
isattheUniversityofBristol,UK
MichaelChorost EVOLUTION,
isawriterbasedinWashingtonDC
StuartClark
isaconsultantforNewScientist EXTINCTION
JamesO’Donoghue The history
isawriterinNorwich,UK
JeffHecht
isaconsultantforNewScientist of life
BobHolmes
isaconsultantforNewScientist
DanJones
isawriterinBrighton,UK
NickLane
isatUniversityCollegeLondon
MichaelMarshall
isdeputyeditoratBBCEarth
MichaellePage
isareporteratNewScientist
PatShipman
isatPennsylvaniaStateUniversity
TobyTyrell
isattheUniversityofSouthampton,UK
Tim Vernimmen
is a writer based near Antwerp,Belguim
Peter Ward
is at the University of WashingtoninSeattle
1
28 Riseofthewatereaters
Howlifegotitsoxygen
32 Genesisrevisited
Didoxygenreallykick-startcomplexlife?
36 Life’slongfuse
Solvingthemysteriesofthefirst complex life
42 Theotherbigbang
The origin HowlifeonEarthtookoff
46 Second coming
of life The truly momentous event in animal
evolution
6 Meetyourmaker
Hominginontheancestorofalllife
10 Dawnoftheliving
Thesearchforthefirstreplicator
14 Inevitable,fluke,orboth?
Iflifeisinevitable,wherearethealiens?
20 Underacoldsun
Howdidlifestartonthisinhospitableplanet?
24 Home and dry
The articles here were first published No primal soup: creating life without water
in New Scientist between April 2007
and February 2015. They have been
updated and revised.
2 | NewScientist: The Collection | Life on Earth: Origins, Evolution, Extinction
3 5 6
Fossils Evolution Extinction
50 Signsofearlylife 76 Theultimateguidetoabeautifultheory 114Deathonamassivescale
Fossils-anexpertguide Bustingthemythsandmisconceptions Aguidetomassextinctions
54 Findthegaps 86 Inthefastlane 120Noah’snightmare
Closinginonthemissinglinks Lifeischangingbeforeourveryeyes Wehavetochoosewhichspeciestosave
60 Turnedtostone 92 TheXfactor 124Earth after life
Thesevenmostrevealingfossilseverfound Asinglegenetoshuffleupnewspecies What if everything died out tomorrow?
4 96 Winningcombinations
Evolvability:cashinginonthegeneticlottery
101Adaptfirst,mutatelater
Isevolutionoutoforder?
105Theascentoflife
Doeslifehaveadirection?
108Unnaturalselection
Humansarethegreatestforceinevolution
Gaia
66 Callintheclouds
Howlivingthingsshapetheweather
70 Gaia’seviltwin
Lifeisitsownworstenemy
74 Gaia: the verdict
Just how motherly is the Earth?
Life on Earth: Origins, Evolution, Extinction | NewScientist: The Collection | 3
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C H A P T E R O N E
THE ORIGIN OF LIFE
NZA
O
AIXSP MEET YOUR
MAKER
Whatdidthelastcommon IN1859,whenCharlesDarwinpublished Sincethenwehavediscoveredamultitude
OnTheOriginofSpecies,hededicatedan ofintermediatelinks:fishthatcouldcrawl,
ancestorofalllifelooklike?
entirechaptertotheproblemofmissing lizardswithmammal-likejaws,whaleswith
MichaelLePagedelves “intermediatelinks”–transitionalformsthat legs,giraffeswithshortnecksandmany
bridgedtheevolutionarygapsbetweenclosely others(see“Findthegaps”,page54).But
intotheprimordialsoup
relatedspecies.Ifhistheorywascorrect,the there’soneweareunlikelyevertofind:the
fossilrecordshouldbefullofthem.Where linkbetweentheearliestproto-lifeandlifeas
werethey? weknowit,alsoknownasthelastuniversal
Atthetimeitwasarealproblem,asfew commonancestor,orLUCA.
suchfossilshadbeenfound.Thencame LUCAlivedaround4billion years ago –
thespectaculardiscovery,in1861,of a tiny, fragile life form that is the direct
Archaeopteryx,withthewingsandfeathers ancestor of every single living thing, from
ofabirdandtheteethandtailofadinosaur. aardvarks to zebras. It wasn’t the very first
6|NewScientist:TheCollection|LifeonEarth:Origins,Evolution,Extinction
These tell us much about what LUCA was
like. We know it used DNA to store recipes
for proteins, for instance. We even know what
many of those recipes were, because many
vital proteins found in all cells today must
have come from LUCA. And from the nature
of these proteins, it is clear that LUCA used
an energy-rich molecule called ATP to fuel
cellular processes, just as our cells do.
How did LUCA make its ATP? Anyone
designing life from scratch would probably
make ATP using chemical reactions inside
thecell.Butthat’snothowitisdone.Instead,
energyfromfoodorsunlightisusedtopower
aprotein“pump”thatshuntshydrogenions–
protons– out of the cell. This creates a
difference in proton concentration, or a
gradient, across the cell membrane. Protons
then flow back into the cell through another
protein embedded in the membrane, which
uses the energy to produce ATP.
Think of a sink
To understand it in energy terms, think of a
double kitchen sink. The small sink represents
the inside of the cell and the large one the
outside world. Start by filling the large sink
with water, leaving the small one empty. The
difference in water levels is a potential source
of energy: drill a hole in the divider and water
will flow into the small sink. The flow could be
used to turn a tiny turbine – which is
essentiallywhattheATP-makingproteinis,
aturbineturnedbyprotonsandotherpositive
ions(seediagram,page8).
This process is so convoluted that when
biochemist Peter Mitchell proposed it in 1961
it was dismissed as nonsense. But it has turned
out to be common to all life, so most biologists
thinkitmustbehowLUCAmadeATP.
Exploitingaprotongradientrequiresa
membranethatisimpermeabletoprotons–
they should only be able to flow in through
the turbine. So it’s assumed that LUCA had
an impermeable membrane. But there is no
life: thousands, if not millions, of years of newworkonaleadinghypothesisforthe evidence that this is the case. In fact, the
evolutionary experimentation preceded it. originoflifemighthavesolvedmanyofthe nature of LUCA’s membrane is an enigma.
But understanding LUCA would give us our mysteries.Itpaintsadetailedpictureofwhere To understand why, we have to backtrack
best view yet of the origin of life. ourearliestancestorlived,howitlivedand to the 1970s, when it was thought that life
We already know a surprising amount. whatitwaslike.Preparetomeetyourmaker. could be divided into two great “empires”.
Although any traces LUCA left in rocks were Darwinhimselfwasamongthefirst In one were animals, plants and fungi, and in
probably obliterated aeons ago, something far scientiststospeculateonhowlifeoriginated: the other the much simpler bacteria. Then
more revealing survives inside today’s living heenvisageda“warmlittlepond,withallsorts microbiologist Carl Woese discovered that
cells: a biological operating system that is ofammoniaandphosphoricsalts,lights,heat, the bacterial empire actually contained two
common to all life and must have been shared electricity,etcpresent”.Wewillprobablynever radically different types of life. A third
by LUCA too. knowexactlyhowLUCAcametobe,butwecan “domain”, now known as archaea, had been
Many features of LUCA, though, have makeeducatedguessesbylookingatsomeof hiding in plain sight.
remained enigmatic, even paradoxical. But thefeaturesoftoday’slivingsystems. Archaea often look like bacteria, and are >
LifeonEarth:Origins,Evolution,Extinction|NewScientist:TheCollection|7
“ The building blocks of life would have
formed spontaneously within the vents”
similar in many ways – as you would expect explain why life uses proton gradients to
given that both evolved from LUCA, probably generate ATP. Now, says Lane, it can also
quite soon after it existed. There are also some explain another of life’s key features: the
fundamental differences between them. membranes of archaea and bacteria.
One is their membranes. Distinct from the better known black
Both bacteria and archaea have membranes smokers, alkaline hydrothermal vents are
made of water-repellent fatty molecules. places where warm alkaline fluids, at
Simple fatty molecules tend to flip around, temperatures of between 40 °C and 90 °C,
making the membrane leaky, so both bacteria well up through cracks in the sea floor. As
and archaea tacked on a water-loving the fluid hits the cold seawater, minerals
phosphate group to stabilise the molecules precipitate out of solution, gradually forming
and make their membranes impermeable. rocky chimneys up to 60 metres tall, full of
They took very different routes, though. narrow channels and pores.
Bacterial membranes are made of fatty acids
bound to the phosphate group while archaeal
Building blocks of life
membranes are made of isoprenes bonded to
phosphate in a different way. This suggests Alkaline vents were present in primordial seas
that their membranes evolved independently. too. Within these ancient vents, Lane, Russell
WA
This leads to something of a paradox: if and Martin think, the building blocks of life NO
LUCA already had an impermeable membrane would have formed spontaneously. The walls
for exploiting proton gradients, why would its would have been rich in iron and sulphide, for interface between the proton-poor alkaline
descendants have independently evolved two example, which can catalyse complex organic vent fluid and the proton-rich seawater. This
different kinds of impermeable membrane? reactions. What’s more, temperature gradients is the ultimate origin of the proton gradients
Nick Lane of University College London, a within the pores should have created high that power life today.
biochemist and award-winning science writer, concentrations of organic compounds and The stage was now set for the evolution, via
has come up with a startling answer that favoured the formation of large molecules, a series of gradual steps, of the turbine protein
challenges many widely held ideas. Far from including lipids – fat molecules – and RNA. that straddles the membrane and produces
being impermeable, LUCA’s membrane was So it would have been a perfect setting for ATP. This was a crucial step in early evolution,
leaky. In fact, he argues, it had to be leaky. the RNA world widely thought to have been though the cells could only survive at the
Lane starts from the assumption that life the first step towards life. This may have been interface between vent fluids and seawater,
originated on the sea floor at places called where self-replicating sets of RNA and other where there was a gradient to exploit. Only
alkaline hydrothermal vents. This was molecules first emerged and began to evolve later did they evolve the ability to generate
proposed in 1989 by Michael Russell of NASA. into cell-like organisms with simple their own gradient using proton pumps.
Its proponents, including Lane and William membranes. These proto-life forms needed It is a neat hypothesis but as critics have
Martin of the University of Dusseldorf in energy – and it was provided, Martin and Lane pointed out, there is a big catch. Early cells that
Germany,havearguedthatitalonecan argue,bythenaturalprotongradientatthe hadtheATPturbineproteinbutnotproton
Life powers up
The earliest life on Earth could well have evolved at an undersea hydrothermal vent around 4 billion years ago. PROTON
How did this cell get its energy, and how did it evolve to colonise the rest of the planet? SODIUMION
The cell lives on the boundary between acid, proton- Later cells evolve a "revolving door" protein that Eventually cells develop a dedicated proton pump
rich seawater, and alkaline vent luid. It develops a efortlessly pumps sodium ions out while letting and a leak-proof membrane. These cells can generate
protein that, like a turbine, extracts energy from the protons in. The sodium later re-enters through the their own proton gradient across the membrane to
proton gradient (diference in concentration) turbine protein, generating even more energy obtain energy, and can leave the vent behind

ACID
SEAWATER
TTUURRBBIINNEE
REEVOOLVINNNGG
DDOORR
PRROOOTON
PUMP
PPPRROOTT
GGRAADIE
LEAKY LEAK-PROOF
MEMBRANE MEMBRANE
ALKALINE
VENT FLUID
8 | NewScientist: The Collection | Life on Earth: Origins, Evolution, Extinction