ARCHAEOLOGY Scientists cannot tell for
sure whether Earth was previously the home
of a civilisation comparable to that of
humans. If the civilisation existed in the
Silurian period 430 million years ago, almost
all evidence would have vanished by now.
The likelihood of finding fossils of a
430-million-year-old intelligent species is
very slight. Before the dinosaurs, we know
of only around 2000 somehow intact
individuals of relatively few species over a
period of 170 million years.
Moreover, almost all artifacts produced
by a civilisation are quickly broken down
through physical, chemical and biological
reactions. Concrete crumbles; iron corrodes;
textiles decay. Only a few materials survive
for millions of years, such as bronze. A statue
like Captain Cook’s in Hyde Park would
survive longer than the rest of Sydney.On a larger scale, geological forces
continuously rearrange the planet’s surface.
Some areas are worn down, and the surface
is washed into the ocean as sand and clay. In
other places, the surface becomes buried by
new soil layers. The oldest preserved ground
surface in the world is thought to be the
Negev desert in Israel, and that is only 1.8
million years old.
Geologists’ most detailed data about the
past comes from drilling into the mud of the
ocean floor. From these stratified cores we
can discover the details of past climate
change, and it could be that global warming
and the effect of humans’ CO 2 emissions
would be the most die-hard evidence of our
own civilisation. But again, the ocean floor is
constantly destroyed and reformed through
plate tectonics, and the oldest ocean floor in
the world is only 170 million years old.Were there civilisations
on Earth before ours?
In the BBC’s Doctor Who series, the Doctor meets intelligent
reptiles from Earth’s Silurian period, 430 million years ago.
Would we be able to find evidence of such a civilisation today?If humans disappeared, plants
would be taking over our cities
before the first decade was out.LIZARDS WOULD BE
IMPOSSIBLE TO FIND
Doctor Who features
a civilisation of lizard-
like creatures from Earth’s
Silurian period 430 million
years ago. If this were true,
evidence of their existence
would be almost impossible
to find today.20 | SCIENCE ILLUSTRATED
SCIENTISTS ANSWER QUESTIONS FROM OUR READERS