Donnerstag, 4. Juni 2009

AW: Let's Do A Time Warp!


Let's Do A Time Warp! – but what we need for it? 1,21 Gigawatts? A Warp 9 suitable space ship and a medium class star? A rift in the space-time continuum as we know it? A time machine?

Or simply an Accretionary Wedge Outside the Interzone?

Unfortunately we still not possess time travel technology, but nevertheless this doesn’t mean we are not capable to go in touch with the past. We not possess the technology to go from the present to the past, but we do possess the ability to bring the past to the present.
And considering time – and if you knew time as well as I do, you wouldn't talk about it - it's him, I’m not so fascinated by a particular point in time, but more on the passing of time.

Earth sciences deal with a fundamental problem; the study object itself is continuously destroying its own history, by rock alteration and erosion. The knowledge of rocks – and all related topics, ranging from fossil content to metamorphic events – therefore becomes more fragmented with increasing age. One might approach this historical perspective also from the opposite side: the younger the rocks, the more of them are still present. This makes the Quaternary by far the most intensively studied period – but nevertheless not necessarily the best understand – in fact, the good preservation of different facies in a restricted area or stratigraphic column, for example in the glacier forefield, is sometimes confusing simply by data excess.

So geologist and palaeontologists have to deal with rocks to reconstruct past environments and their change trough time. But not always rocks are well exposed or accessible; the bedrock is usually covered by younger soil material and/or vegetation. Even quaternary or recent sediments –often hidden only some meters under the landscape– are not always easy to reach. But like the old saying, if the mountain doesn’t came to Moses, Moses has to go to the mountain.

One possibility to recover sediments from the underground is by drilling them. If minor depths have to be reached, hand boring is a cheap and effective method. This method use is only limited by the penetration power – number of peoples pushing the borer in the underground, and by the increasing length and so weight of the rod system that can be handled and recovered. The method can largely used, for example to sample bogs, swamps and lakes in different terrain, from coastal swamps to small mountain bogs or lakes.



The recovered sediment samples can contain a lot of information’s:

-grain size distribution can give hinds for past erosion phases, large mineral grains or pebbles normally represent strong import of eroded material
- the colour of sediments give first information’s of deposition conditions, for example black sediments can show anaerobic deposition conditions
- the found minerals and chemical composition can give clues on catchment area, or chemical processes in the deposition environment
- pollen and spores can give hinds to reconstruct vegetation successions and changes trough time, and also climatic changes
- animal parts, like from arthropods, insects, microbes and even vertebrates also give precious information’s to reconstruct the past environment



So let’s see a typical sedimentation succession of some meters thickness in a former glaciated area of mid latitude, recovered by hand boring in a bog.


The basin of the former lake is commonly formed of bedrock or impermeable morain deposits of the last glacial maximum. Over them follows grey clays or silt, with no or only weak stratification, and no apparent fossil content. This sediments change gradually in white marls whit small gasteropods and bivalves, only a grey band is outstanding. Then there is a more or less distinct change in brown, plant detritus rich peaty material, with rare parts of insects.

Based on study on the fossil content, the sedimentology and deposition environment, and comparing the results with modern lakes and bogs and their fauna and flora, an attempt to imagine the story that this boring core can tell us can be undertaken.

10.000 to 18.000 years ago the great glaciers retreaded for the last time, uncovering a barren landscape, lacking vegetation cover. The basins carved by the glaciers where filled by time with water and mud, transported by rivers still feeded by small glaciers. This mud will form the grey clays. Still more time passes, the climate is warmer, the last ice melted, and the basin now is a lake surrounded by dense forests. One day of 11.000 years ago suddenly a black cloud covers the sky, and a fine, grey dust falls on the lake, where it sinks to the ground and deposits. Some hundred km distant from the lake the Laacher See Volcano erupted, covering half Europe with a small band of distinctive, grey ash.



But this event doesn’t disturb the community of animals living in the swallow, warm lake, and the carbonat rich catchment provides a high aviability for dissolved calcium in the water, an ideal habitat for a rich variety of mollusc.
More and more biogen marls deposit, filling slowly over millenia, but inexorably the basin. Plants grow in the swallow part of the lake, first mosses and aquatic plants, accumulating organic detritus and peaty material. In the middle of the forest a treeless plane extends - a bog has taken the place of the lake.



Finally, in the last centimetres’ of peaty deposits, pollen grains of cereals and other cultivated plants suggest first human settlements in the region. And only in the last millimetres’ our civilization and earth sciences develops methods to study the hidden archives of bog sediments – but also to destroy them. Lakes, swamps and bogs are one of the most threatened ecosystems in industrialized countries, threatened by urbanization and agricultural use.

All this happened in the last 10.000 years, in a single point – now consider the age and the vastity and diversity of earth itself. Realizing the age and changes in environment, flora and fauna that occurred, we obviously have to reconsider our relationship to earth and other species and also our place in earth history.

This maybe is the most important message that drilling trough time can give us.


REFERENCES:

VAN LOON, A.J. (2000): The strangest 0.05% of the geological history. Earth-Science Reviews 50: 125-133

Kommentare:

Lockwood hat gesagt…

Thanks for the shout-out, Dave! Hope you can offer a space-time field trip for the wedge. We'd really like to get it back on its feet!

Lockwood hat gesagt…

Logged and queued. Thanks again!