Hominid Fossils and Eustasy

The effects of eustacy (world-wide changes in
sea-levels) on human/hominid and other fossils
have never been recognised.

We can all appreciate the enormously destructive
effect that waves have on a beach. Every beach
is a giant milling machine. On most kilometres of
most beaches, thousands of tons of rocks, pebbles
and sand are moved along hundreds of metres
each year. Any fossils that become exposed on a
beach will be rapidly ground into tiny particles.

This is well known. But what is not widely
appreciated is that over each 100 to 150 Kyr,
beaches move inland, often for hundreds of miles,
and then retreat, and advance and retreat again,
and do so repeatedly. Within the broad 100-150
Kyr movements, there are dozens or hundreds of
shorter-term ones, when the sea advances or
retreats relatively short distances. As the coasts
advance, they will chew up virtually all the soft
surface soil, as well as some hard rock.

This means that for terrestrial species, such as
hominids, which live at, or close to, sea-level,
very few fossils will survive in their natural habitat.
The only members of such species that are likely
to leave fossils are those which have moved away
from their habitat to higher ground, usually
seeking (or migrating to) other habitable sites.
They are often likely to die en route on such high
ground, and will sometimes leave fossils in such
locations -- giving an entirely misleading
impression of the nature of their normal habitat
to those who discover them.

Eustatic sea-levels are shown at this site:

http://en.wikipedia.org/wiki/Sea_level_rise#Local_and_eustatic_sea_level

It might be thought that the fossils of hominid
(and other such species) could be located at
sites just above the point of the highest recorded
sea-level. Unfortunately, the time concerned is
likely to have been so brief as to barely register.
Instead of finding fossils from the whole of, say,
a 5 Myr record, we are obliged to look for them
in a layer which is only about one thousandth as
deep.

Fossils of hominids and other similar species
are likely to survive most often in geographical
locations which have experienced continuous
uplift since they were deposited -- thus enabling
them to escape coastal erosion. That is probably
why the Afar region is so rich in fossils.


Paul.






.

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