heya! i have a question about fossils!!?

Question

heya, why do fossils appear in some rocks more than other rocks?? thnx!!

Answer 1

Some rocks are formed from magma (lava) that comes from deep in the earth. THose rocks never have fossils because, hey, they were like, 2000 degrees and anything close to them was burned totally.

Some rocks were formed from deposits at the bottom of ponds, rivers, mud flats along the ocean, and in the shallow ocean. Those kinds of rocks (shale, limestone) can have lots of fossils. Let's say that you had a pond at the end of a river where it meets the sea. Lots of dead stuff could float down the river and get caught in the mud. Then it would gradually get covered by more mud. After thousands or millions of years the mud would be really thick. It would be formed into rocks with the remains of the dead animals in it. Bingo. That's a fossil.

There are lots of grat books about fossils. Check it out at your local library. And most places in the USA there are rocks near you where you could go and dig up your own fossils. That would be cool.

Answer 2

How rich in fossils a sedimentary rock is depends on a few factors.

1) Abundance of fossilisable organisms in the environment the rock formed in.

2) Sedimentation rate. If sediment accumulates very fast, then there will be less time for generations and generations of fossilisable organisms to live and die there. Also, the 'accomodation space' (ie. the hole in the ground) will fill up very fast and that's it over (for a while). At the other extreme, if sedimentation is too slow then there won't be anything to bury the fossils. They will decay away before they get buried.

3) Preservation in the ancient environment. Most shells and things are pretty fragile. And some environments are pretty tough on them, eg. a lot of beaches are made mainly of sand made from broken shells.

4) Preservation in the ground over geological time. This depends a lot on the chemistry in side the rock and how the rock cements together from the original sediment. Most remains that get buried dissolve away and aren't replaced with other material. The soft sediment squishes in under the weight of everything above, and all trace is gone.

Answer 3

Depends on the rock and its depositional environment. Fossils are not animals, but are impressions of what once was an animal. Igneous rocks do not contain fossils, metamorphic rocks may, but they might also be distorted or destroyed. Sedimentary rocks are the most receptive. But, conditions have to be just right to preserve the fossil impressions. Sandstones can contain fossils, but often there is too much energy in their environments to preserve any but the stoutest fossils. Shales, mudstones, and limestones often make the best placed to find fossils. They are very fine grained and are deposited in relatively quiet waters. A leaf or brachipod shell dies and settles to the bottom. If the water is lacking oxygen, so the potential fossil doesn't rot, it will gradually be covered by sediments. Eventually the animal will be replaced by the sediments, filling in its impression. Time and pressure will eventually lithify the sediments into solid rock. If you are lucky enough to pick a piece of that rock up and split it, you are the first one to see that fossil in millions of years! Just remember, fossils, with a few exceptions, are made up of their host rock. A brachipod found in limestone, is still limestone.

Answer 4

There are 3 types of rock -

1 Igneous rock.... This is formed from volcanoes. If prehistoric life got caught up, it would be burned, and therefore no trace of fossils would be found.

2. Metamorphic rock ....... Is rock that has changed from one form to another due heat or extreme pressure. Fossils may survive in metamorphic rock.

3. Sedimentary rock - is formed by layers of mud or sand (sediment) pressing on top of each other to form rock. This kind of rock provides the best environment for fossils. However, once the sedimatary rock is formed, it can be metamorphised to another type of rock and the fossil may be preserved.

Also, many rocks we see are just not old enough to hold fossils. You generally have to go looking in mines and such places where old rocks have been exposed.

Hope this helps.

Answer 5

If the rocks are older, then the fossills will be reletive to the age of the rock. eg. you won't find a t-rex in rocks that are 200million years old because t-rex was only 65million years ago. Also the fossils could still be deep under ground and will eventually appear when they arrive at the surface due to erosion.

Answer 6

All the above answers are fine but one additional thing there may not be any thing there. There are even today large areas of land where there are very few thing to fossilise eg the mid Sahara the valleys in the mountains of Antarctica etc also land animals only really developed in the Devonian about 350 million years ago before this no land animals so no land fossils.

Answer 7

For one answer, think of roughly those 2 issues mutually to come back to a end: (a) sedimentary rocks incorporate layers formed from being deposited 300 and sixty 5 days after 300 and sixty 5 days and then hardening (b) something happens in the international the place there is diverse stuff falling out of the sky or being deposited from water - ought to point climate or eruptions, etc. for yet another answer, think of roughly those and are available to a end: (a) sedimentary rocks are often formed horizontally (b) many circumstances in hills/mountains you may word layers that are at angles or have been overturned... -what ought to this point out?

Answer 8

Yes, of course, it depends on the type of rock. Rocks are graded on a hardness scale known as the Mohs scale. Devised in 1822 by Friedrich Mohs, a German minerologist, the Mohs scale grades the hardness of rocks by grading them in relation to ten well known rocks. Most fossils are found in sedimentary rock, which is the most common type of rock on earth. Sedimentary rocks form when particles of sediment are deposited by water or wind, and then (in most cases) hardened or consolidated through time. Occasionally fossils occur in materials other than sedimentary rock, such as ancient tree resin (amber), in which insects or other small animals became stuck and entombed. Similarly, bones of mammoths, saber-tooth cats, and other extinct animals have been found in tar pits, in which unfortunate animals became trapped and mired. Generally speaking, igneous rocks are softer than metamorphic, although metamorphic rock sometimes holds more fossilized remains due to the fluid nature of their beginning state.

Answer 9

Yes they do. Often type of rock are found and THEN they look for th efossils in those rocks

Answer 10

It all depends on the type of rock. Sedimentary or from an ice burg or from a volcano.