Sixteen real places are open to you, on every continent. At each one you
read the rock layers that are exposed there. Then you use what you find to build
one timeline of Earth's history. Three or four places are enough to build it, and
the rest are there to test it.
Model details
Every landscape in this simulation is a measured place. Nine of the
sixteen places are built from a survey flown over the ground, and
coloured with real aerial photographs. The finest of those surveys
measures the ground once every square metre. Others measure it every
five or ten metres. The ground right under an outcrop is always the
most finely measured part of a site, and the wide view around it is
coarser. Seven sites have no flown survey we could use. There the
ground comes from a 30-metre satellite elevation model, and the colour
from satellite images. Heights are shown at true scale, with no
vertical stretching. Every site is entered from the same height of two
kilometres. That is what makes the sizes you see comparable.
On steep ground the aerial photograph has almost nothing to show,
because it was taken from straight above. There the simulation paints
the rock unit that geologists measured at that height. It uses the
unit's published colour and thickness, so the same unit appears at the
same height on every wall in view. In the drawn columns each rock also
carries its FGDC lithology pattern. The units, their fossils and the
marker beds are taken from published surveys of each site, cited in
the simulation's data files.
The rock layers give you the order of events and nothing more. Naming
an age in years takes laboratory dating. This simulation treats a date
as information arriving from outside the rocks. That is how the real
time scale was built.
The photographs of fossils and rocks are of real specimens. Some are
from the very layer you are reading. Others show the same kind of
fossil from a different place, where no photograph of this layer
could be found. Every picture is listed under Photographs, with
where it came from.
On the timeline the height of a bar is not the thickness of its rock
to scale. The beds at these places run from a few centimetres to half
a kilometre thick. A bar does grow with the thickness of its bed, but
far more slowly, so that the thinnest bed can still be seen and
pressed. The height of a bar on the board carries the order of the
layers. It carries their ages in years only once you press See it to
scale.
Photographs
Every photograph in this simulation, with the person who took it and
the licence it is shared under. Press a title to open the original, or
a licence to read its terms.
Each photograph has been resized, and some have been cropped, to fit
the space they are shown in. None has been altered in any other way.