What Are Fossils?

Fossils are the remains or marks of plants and animals that lived a very long time ago. They are usually found in rocks and stones. Fossils are important because they tell us a story about things that lived on the earth before us.

What Things Become Fossils?
Animals and plants become fossils. So do nests, eggs, footprints and even animal droppings!

How are Fossils Made?
Fossils are made from the hard parts of plants and animals, such as:-bark, seed cases, bones and teeth. These parts do not easily rot away after plants and animals die. Fossils take millions of years to form.

Turning to Stone
For example: -A star fish dies.-The soft parts of its body rot away quickly. The harder parts slowly get covered by mud. After millions of years, the star fish is deep in the ground. The mud around it is crushed by the land on top and-turned to stone. So are the remains of the star fish. Millions of years later, the stone gets worn away and the- fossil can be seen.

Kinds of fossils

Body Fossils – include the remains of organisms that were once living. Usually only the hard parts of animals like shells and teeth and bones become fossilized. However, feathers, fur, and skin have also been found.

Trace Fossils- are the signs that organisms were once present. Trace fossils can be tracks, footprints, trails, burrows, eggs, nests, leaf impressions, and feces. Take a peek at these Images of trace fossils

There are also fossil plants

Where are fossils found?
Fossils may be found almost anywhere sedimentary rocks are exposed.
Sedimentary rocks are rocks that formed when layers of sediment such as clay, mud, silt, or sand hardened over millions of years. These types of sediments settle down in lakes, swamps and oceans. This is one of the reasons why most fossils are the remains of animals who lived in or near the water.

What do fossils tell us?
Rock layers can tell us Earth’s history because they preserve past events. Fossils help scientists determine the age of the layered rocks. Fossils also tell us what happened in Earth’s history and when it happened. Fossils can be used to recognize rocks of the same or different ages. They are clues to former life

Who Studies Fossils?
A paleontologist is a scientist who studies fossils.

Flow chart of fossil formation:

HOW FOSSILS FORM
Fossils of hard mineral parts (like bones and teeth) were formed as follows:

* Some animals were quickly buried after their death (by sinking in mud, being buried in a sand storm, etc.). * Over time, more and more sediment covered the remains. * The parts of the animals that didn’t rot (usually the harder parts likes bones and teeth) were encased in the newly-formed sediment. * In the right circumstances (no scavengers, quick burial, not much weathering), parts of the animal turned into fossils over time. * After a long time, the chemicals in the buried animals’ bodies underwent a series of changes. As the bone slowly decayed, water infused with minerals seeped into the bone and replaced the chemicals in the bone with rock-like minerals. The process of fossilization involves the dissolving and replacement of the original minerals in the object with other minerals (and/or per mineralization, the filling up of spaces in fossils with minerals, and/or recrystallization in which a mineral crystal changes its form). * This process results in a heavy, rock-like copy of the original object – a fossil. The fossil has the same shape as the original object, but is chemically more like a rock! Some of the original hydroxy-apatite (a major bone consitiuent) remains, although it is saturated with silica (rock).

There are six ways that organisms can turn into fossils, including: * Unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree sap) * Per mineralization=petrifaction (in which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil – can preserve hard and soft parts – most bone and wood fossils are per mineralized) * Replacement (An organism’s hard parts dissolve and are replaced by other minerals, like calcite, silica, pyrite, or iron) * Carbonization=coalification (in which only the carbon remains in the specimen – other elements, like hydrogen, oxygen, and nitrogen are removed) * Recrystallization (hard parts either revert to more stable minerals or small crystals turn into larger crystals) * Authigenic preservation (molds and casts of organisms that have been destroyed or dissolved). Most animals did not fossilize; they simply decayed and were lost from the fossil record. Paleontologists estimate that only a small percentage of the dinosaur genera that ever lived have been or will be found as fossils.

Most of the dinosaur skeletons that are shown in museums are not actually fossils! Exhibits are often lightweight fiberglass or resin replicas of the original fossils.

Why are Fossils Rock-Colored?
Because they ARE rocks! A fossilized object is just a rocky model of an ancient object. A fossil is composed of different materials than the original object was. During the fossilization process, the original atoms are replaced by new minerals, so a fossil doesn’t have the same color (or chemical composition) as the original object. Fossils come in many colors and are made of many different types of minerals, depending on what the surrounding rock matrix was composed of; one dinosaur bone (Minmi) is an opal. When Did They Live?

• First Fish 570 million years ago.
• First plants on land 440 million years ago.
• First insects and amphibians 400 million years ago.
• First reptiles 360 million years ago.
• First dinosaurs 245 million years ago.
• First birds 210 million years ago.
Also, some fossils of skin (and other soft body parts) have been found. Again, the color of the skin is not retained during the fossilization process, all that remains today is a rocky model of the original.

From the Sea
* The first creatures on the earth lived in the sea.
* Some sea creatures made good fossils because they had hard shells and hard bones

Fish Fossil

Horse shoe crab Fossil

Trilobite Fossil

Plants
•At first, there were only living things in the sea.
•Slowly, over millions of years, plants began to grow on the land. •Some of these plants have S left fossils in the rock.

Animals
•Animal fossils are often bones that have been turned to rock. Sometimes part of the flesh is preserved, but most of the time only skeletons remain. •Because of this, it is more difficult to find fossils of in vertebrates. (Invertebrates are animals that don’t have bones ) •We have discovered several types of animal fossils: bones, skin, teeth, claws, eggs, nests, muscles, and organs , which tell us how much animals and dinosaurs weighed and how they might have walked.