Digging Deeper
WHAT ARE FOSSILS?
Earth is very, very old. I
n earlier times, all kinds
of plant and animal spe
cies lived on Earth; they
no longer exist because t
hey have since become
extinct. The best-known e
xtinct animal species
are no doubt the dinosa
urs.
We know about extinct a
nimal species because in
many places the remain
s of their bodies — for
example, their bones, im
pressions of their skin in
stone, or their footprints — h
ave been preserved.
Sometimes, the entire bo
dies of insects are even
preserved in amber.
Let’s dig into the world o
f fossils and the history
of Earth!
WHY FOSSILS ARE EXCITING
Fossils show us how life deve
loped on Earth. Throughout m
ost of Earth’s history,
the only life forms were the s
ize of bacteria. In more recent r
ock, the remains of
larger animals can be found
—
but only sea creatures such a
s ammonites and fish.
Only much later did plants a
nd then animals conquer dry l
and.
The younger the fossil-bearin
g rock, the more highly develo
ped are the classes of
life forms that can be found w
ithin them. The first land anim
als were insects and
amphibians that had develop
ed from fish. After that, reptil
es arose; they were
better adapted to life on land
. They in turn were the ancesto
rs of dinosaurs and
mammals, with birds then d
eveloping out of a
group of dinosaurs.
Over and over, entire groups o
f animals became
extinct again
—
sometimes due to catastroph
ic
events. The dinosaurs (and m
any other species
living at the time) were wiped o
ut by a massive
asteroid impact.
HOW FOSSILS ARE MADE
When animals die, scavengers
eat their remains or they decay
over time. Only in very rare
cases are their bones or imprints
saved. This may happen, for
example, when they become
embedded in sludge, which can
preserve the remains well due to
its low oxygen content.
Over time, mineral layers, or
strata,
may settle on top of them
and protect the animals’
remains. Although the flesh
itself will quickly decay,
mineral-rich groundwater may
penetrate the spaces that
remain behind. This causes the
embedded bones to “turn to
stone”: the bone material is
replaced by minerals, with the
shape of the bone remaining
intact. In some areas
rain and
wind
may then carry off the
superimposed layers over
millions of years, revealing the
fossils at the surface, where
they can be dug up. Of course,
many more remain undiscovered
beneath Earth’s surface.
