bjones
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For science geeks like me, fossils are about the coolest things in the world. Fossils tell us the story of the history of life on Earth. Fossils take a couple of different forms but they all involve a record of life forms preserved in rock. Some fossils are imprints in rock that show animals or plants were once there. These are called trace fossils. Other fossils are the preserved form of the plants or animals themselves. No matter which type they are, fossils are formed in a similar manner and tell us about how life originated, changed, and evolved on the planet.
To understand how fossils are made, we have to understand a little bit about geology and rock formations. Fossils are found in the top layer of the Earth, called the crust. Most of the rock in the Earth’s crust is sedimentary rock. Sedimentary rock is formed whey sand, dirt, and other small particles are collected together. Over time, more and more particles may collect. The particles on the bottom are pressed together and as water seeps down into them, minerals are collected in the gaps. Eventually, the particles become dense and hard, forming a layer of rock. Through time, layers are continually added on top of the old ones.
Normally, plants and animals decompose within a few years. Sometimes, animals and plants die in places with lots of moving particles, or sediment, that eventually forms sedimentary rock. Some places with lots of sediment are river beds, lakes, and oceans. The sediment quickly covers the organisms, giving them some protection from decomposition. Eventually, the softer parts of the animal or plant decompose but the harder parts remain like bones, teeth, and claws. Water slowly washes or trickles through the bones, or other hard parts of the organism, carrying very tiny particles of sediment and minerals. Some of the minerals begin to stick and, after time, cover the entire part. In addition, water enters the inside of the hard matter and minerals begin to fill in the entire bone. After thousands and millions of years, minerals and bones merge into one rock-like formation. So, fossils are a mixture of rock and the original organism. The sediment around the fossil eventually becomes sedimentary rock with fossils embedded inside.
 Posted 5427 day ago
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