KRK FOSSILS
EARTHCACHE: FOSSILS
Fosil je ostatak životinje ili biljke (ljuska, ljuska, kost, zub, sjeme, lišće, spore, pelud, plankton, mikroorganizmi), općenito mineraliziran ili njegova jednostavna plijesan, sačuvana u sedimentnoj stijeni. Fosili i procesi fosilizacije proučavaju se prvenstveno u okviru paleontologije, ali i u okviru geologije, ljudske prapovijesti i arheologije.
Formiranje fosila:
Obično biljke i životinje, uključujući i nas, umiru, trunu i nestaju bez traga. Međutim, ako su ispunjeni određeni uvjeti, organizmi mogu ostati relativno dobro očuvani gotovo zauvijek! Pogledajte samo fosile dinosaura koji su stari oko 230 milijuna godina, ili još bolje, fosilne bakterije čija je starost u milijardama godina.
Postoji nekoliko vrsta fosila, neki su rjeđi od drugih. Organizmi zamrznuti u ledu i zarobljeni u katranu, smoli ili jantaru također se nazivaju fosili. U tim se slučajevima uzorci čuvaju gotovo cijeli. Navedimo na primjer mamute pronađene u vrlo dobrom stanju u sibirskom permafrostu ili nesretne kukce zaglavljene od pleistocena u katranskim jamama La Brea Tar Pits, u današnjem Los Angelesu. Ali najčešći fosili nastaju u sedimentima.
Fosilizacija je dugotrajan fizikalno-kemijski proces
Općenito, da bi se formirao fosil, sediment - blato ili pijesak - mora prilično brzo prekriti tijelo organizma. Meko tkivo se vrlo brzo razgrađuje, pa je ostao samo kostur (ili čak i školjka). S vremenom se sediment nastavlja taložiti na vrhu kostura. Završava zakopan pod debelim slojevima gdje pritisak postaje toliko jak da pretvara sedimente u tvrdu stijenu.
Sada je kostur prepušten na milost i nemilost podzemnoj vodi, opterećenoj mineralima, koja prodire kroz stijenu. Tada se može pojaviti nekoliko scenarija: ili minerali kristaliziraju unutar kostiju i transformiraju ih u fosile; ili se kosti potpuno otapaju i oblik kostura ostaje utisnut u stijenu. Minerali na kraju mogu ispuniti prostor koji ostavljaju otopljene kosti, kao da ispunjavaju kalup. Nakon što su formirani, fosili čekaju da budu otkriveni, što se događa ako se sedimentni slojevi izdižu na površinu, nakon geoloških potresa.
Zadaci:
1. Sadrži li ovaj vapnenac mnogo ili malo fosila?
2. Što to govori o uvjetima koji su vladali u moru u to vrijeme?
3. Opišite oblik lokalnih fosila.
4. Snimite fotografiju sa sobom ili GPS-om u blizini GZ.
Izvori: Wikipedia
KRK FOSSILS
EARTHCACHE: FOSSILS
A fossil is the rest of an animal or a plant (shell, shell, bone, tooth, seed, leaves, spore, pollen, plankton, microorganisms), generally mineralized, or its simple mold, preserved in a sedimentary rock. Fossils and fossilization processes are studied primarily within the framework of paleontology, but also within those of geology, human prehistory and archeology.
Formation of fossils:
Usually, plants and animals, including us, die, rot and disappear without a trace. However, if certain conditions are met, organisms can remain relatively well preserved almost forever! Just look at the dinosaur fossils that are around 230 million years old, or better yet, the fossil bacteria whose age is in the billions of years.
There are several types of fossils, some rarer than others. Organisms frozen in ice and trapped in tar, resin or amber are also called fossils. In these cases, the specimens are kept almost whole. Let us cite for example the mammoths found in very good condition in the Siberian permafrost or the unfortunate insects stuck since the Pleistocene in the tar pits of La Brea Tar Pits, in present-day Los Angeles. But the most common fossils form in sediments.
Fossilization is a long physicochemical process
In general, to form a fossil, sediment - mud or sand - must cover the body of the organism fairly quickly. Soft tissue decomposes very quickly, so all that's left is the skeleton (or even the shell). Over time, sediment continues to settle on top of the skeleton. It ends up buried under thick layers where the pressure becomes so strong that it transforms the sediments into hard rock.
Now the skeleton is at the mercy of underground water, laden with minerals, which seeps through the rock. Several scenarios can then arise: either the minerals crystallize inside the bones and transform them into fossils; or the bones dissolve completely and the shape of the skeleton remains imprinted in the rock. The minerals can eventually fill in the space left by dissolved bones, as if they were filling a mold. Once formed, the fossils wait to be discovered, which happens if the sedimentary strata rise to the surface, following geological upheavals.
Tasks:
1. Does this limestone contain many or few fossils?
2. What does this say about the conditions that prevailed in the sea at the time?
3. Describe the shape of the local fossils.
4. Take a photo with you or GPS near GZ.