How do footprints survive?

[TRB]

Some 800,000 year old footprints have been found in Norfolk ( from the Beeb)

Now, I'll happily admit I'm a bit stupid, but just how do they survive? The land would have been soft enough to leave a footprint, but surely if a print was in, and surrounded by, similar soft material it would fill in with a little help with the elements. Then, when left buried for hundreds of thousands of years, the momentary weight of a body would be insignificant.

It's not exactly keeping me awake at night, just curious!

[otolith]

An imprint in one material can get filled in with another. The thing you have to keep in mind is that fossilisation is relatively rare. Most footprints don't persist.

[Eric Mc]

Footorints in mud can survive if the mud dries quickly and is then infilled by more sediment. The sediment has to then survive in its layer and then be re-exposed for it to reveal the footprints hundreds of thousands - or even millions of years later. There are quite a few sets of dinosaur footprints at various locations around the world. They vary between 65 to 200 million years old.
In Scotland there is a set of footprints left by a centipede the size of a cow - and they are about 400 million years old.

[Simpo Two]

Eric Mc said:

a centipede the size of a cow

Something's not right - the spiracle system of breathing used by insects doesn't work in large bodies. That's why there aren't any big insects.

[TheEnd]

http://en.wikipedia.org/wiki/Arthropleura


Insect size tends to be limited by atmospheric oxygen, so now they can only get so big, but back in times with different oxygen levels, they could have been far bigger, like this fella-
http://en.wikipedia.org/wiki/Meganeura

[MocMocaMoc]

Simpo Two said:

Eric Mc said:

a centipede the size of a cow

Something's not right - the spiracle system of breathing used by insects doesn't work in large bodies. That's why there aren't any big insects.

Nu uh. You just don't want to believe because a centipede the size of a cow would haunt your f*cking nightmares. Forever.

[Simpo Two]

Was the oxygen content of the atmosphere ever significantly greater than it is now?

Perhaps these large insects had some kind of simple pumping system to encourage air to diffuse in and out.


(NB Note a 2' wingspan is not relveant as such; wings don't require oxygen and the associated body is thin. It's a surface area/volume ratio thing).

[Einion Yrth]

Simpo Two said:

Was the oxygen content of the atmosphere ever significantly greater than it is now?

In short, yes: more lengthily this may be of interest.

[otolith]

Centipedes ain't insects!

Oxygen levels were around 50% higher than now when giant arthropods were around, though.

[Eric Mc]

Simpo Two said:

Eric Mc said:

a centipede the size of a cow

Something's not right - the spiracle system of breathing used by insects doesn't work in large bodies. That's why there aren't any big insects.

The world was a very different place 350 - 400 million years ago. There was a much higher oxygen content in the atmosphere. There were also dragonflies with three-four foot wingspans.

[Simpo Two]

Einion Yrth said:

Simpo Two said:

Was the oxygen content of the atmosphere ever significantly greater than it is now?

In short, yes: more lengthily this may be of interest.

Every day's a schoolday!

[Catatafish]

There were also epochs with much higher concentrations of CO2 in the atmosphere, but don't tell the climate apocalypse mob

[Shaolin]

Eric Mc said:

The world was a very different place 350 - 400 million years ago. There was a much higher oxygen content in the atmosphere.

Evidence of much more common and widespread wildfires too as a result.

[Eric Mc]

Probably because the amphibians of the Carboniferous were heavy smokers.

[northwest monkey]

MocMocaMoc said:

Nu uh. You just don't want to believe because a centipede the size of a cow would haunt your f*cking nightmares. Forever.

And this is the correct answer.

I screamed like a girl and ran around waving my arms a lot a couple of years ago when a moth the size of a tennis ball flew into my face, cow size centipedes would be far worse.