THE FUNDAMENTALS OF LIFE
GETTY,^D^ KELLEY/M^ELEND/UNIVERSITY^ OF^ WASHINGTONStromatolites, like these in Australia, formed from
ancient microbes up to 3.5 billion years agoTHE
ORIGIN OF LIFE
There are millions of species alive on Earth today.
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Q
How long ago did life get started
on Earth?A
Around four billion years ago,
when the Earth was still
partially molten and under heavy
bombardment from meteors, the very
first life-like systems appeared.
Somehow, chemicals developed life-
like properties – using matter and
energy from the hellish environment
to ma ke more of t hemselves. Origin-of-
life researchers are still trying to work
out exactly how, during this period,
chemistry suddenly became biology.
Once basic biological systems
formed, life never looked back,
evolving into the two enormously
diverse groups of microbes now
known as bacteria and archaea. A
merger between two of these ancient
cell types, billions of yea rs later, is
thought to have given rise to more
complex, multicellular organisms –
including us, and all the plants, fungi
and animals that ever lived.
Q
How exactly did life on
Earth begin?A
Unfortunately, there is no
consensus or standard model
to explain how life started on Earth.
However, most theories are based on
the idea that at some point early in the
planet’s history, chemicals developed
characteristics that are found in all
living cells today – the ability to self-
replicate, for example, or to produce
other useful biological molecules.
Once such biological characteristics
emerged, a sort of ‘chemical evolution’
was set in motion: chemicals made
copies of themselves, some emerging
with variations that made them either
more or less eff icient, or helped t hem
cooperate with others. The variants
t hat worked best made more copies ofthemselves, while the others were
outcompeted for raw materials.
Over billions of generations, more
complex variations emerged, with
the basic molecular processes of life
enclosed within a membrane. These
cell-like structures were essentially
the first microbial cells, from which
all life evolved.
More fanciful theories suggest that
life on Earth was ‘seeded’ by ancient
microbes falling from space.Q
What is the earliest evidence
of life on Earth?A
The oldest cells ever found
are fossilised in rocks dated
to around 3-3.4 billion years ago.
These early cells look a bit like
cyanobacteria, which is still abundant
today. They were likely to have been
thermophiles, meaning they liked hot
places, and autotrophs, meaning they
made their own complex organic
compounds from simple chemicals.
Further back in time, there must have
been a n older type of orga nism f rom
which these cells evolved.
Other evidence of ancient life can be
seen in t he for m of st romatolites –
rocky st r uctu res for med f rom t he
gritty deposits of vast sheets of a ncient
microbes f loating in t he sea. Some of
these, found in Western Australia, are
thought to be up to 3.5 billion years 5