The fossilized remains of once-living organisms -- animal, plants and humans -- offer scientists a glimpse into past. Fossils have long fascinated both paleontologists and enthusiasts for their ability to tell a story of a time long past. Most fossils show the shape of activity of extinct creatures and human ancestors, but some come from species that exist today.
Fossils Only Form Under Specific Conditions
Most of the organisms that died out long ago never became fossils: conditions need to be just right. Many fossils form on the sea floor, an animal dies, and sinks or gets swept to the bottom of the ocean, where its body rots away. Over time, the sediment around the bone hardens and the bone dissolves, forming a mold. The water slowly deposits its minerals in the mold, making a fossil.
Not All Fossils Are the Same
While some fossils show the skeleton of a long-dead creature, others are more subtle. Sometimes when a dinosaur stepped in muddy areas, sand filled the tracks before they washed away. With time the sand hardens, leaving behind a fossil of a footprint, called a trace fossil. From these, scientists learn about the behaviors of extinct species.
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Humans Learn From Fossils
Whether the fossils are of humans or dinosaurs, they can teach scientists much about species and cultures that existed in the past. Scientists use fossils to make educated guesses about the evolution of different species, and what the climate was like in eras long past.
Scientists Can Tell How Old They Are
Researchers have a few ways of telling the age of a fossil, depending on the rough estimate of when it formed. For instance, aging particularly old fossils requires Carbon-14 dating, a process by which scientists study the radioactive decay of elements in the fossil. Scientists can age more recent fossils by a process called the molecular genetic clock, which compares the differences in DNA between a fossil and similar species alive today. Because DNA rapidly decays, it can only be used on older specimen.
Working with Fossils Isn't an Exact Science
As these fossilized species no-longer exist, scientists can really only guess about the true nature of the creatures from which they came. While in previous years, scientists believed dinosaurs to be scaled, recent interpretations of fossils suggest they had feathers.
Oldest Fossils Are Bacteria
Scientists studying sedimentary rocks on Greenland found small graphite microparticles believed to be the fossilized remains of byproducts produced by ancient bacteria, one of the earliest forms of life from 3.7 billion years ago.
Some Fossils Are Huge
In 2017, scientists discovered the remains of what they now believe to be the world's largest land animal. Called Patagotitan mayorum, the fossilized remains suggest that the long-necked creature was 120-feet long, and possibly weighed 69 tonnes, over 150,000 pounds. Even creepy-crawlies were larger in pre-history. University of Manitoba paleontologists found the remains of a 28-inch long trilobite while searching for fossils near Hudson Bay.
Fossils Reveal Facts About Catastrophes
After a while, some fossilized species stopped showing up, suggesting that those species went extinct. Scientists date one such event to 65 million years ago and suggest that a giant meteorite crashed into Earth and killed many of the species. Fossil records also exist for the species that survived this event, and how it changed their physiology.
Sorry, Cars Don't Run on Dead Dinosaurs
Massive lumbering dinosaurs did not create fossil fuels. Rather, it was microscopic organisms called diatoms. Fossil fuel, a non-renewable resource, formed from these tiny creatures dying in large numbers. Pressure and temperature on the sedimentary rock which covered their remains converted the remaining carbon from their bodies into fuel.
Fossils Are a Finite Resource
Like fossil fuels, fossils themselves are becoming increasingly rare. Since it takes a long time for them to form, and they form under specific conditions, the reservoir of fossils in the Earth grows smaller and smaller each time a scientist takes one out of the ground.