Fossils and Extinction

• Studying fossils is important because most of the organisms that have ever lived are now extinct, and the only way to learn about them is by looking at what they've left behind.
• Fossils are things that have been left behind by long dead organisms, which could be skeletons made of rock, impressions in the ground, or entire organisms that haven't decayed yet.
• Fossils provide evidence for evolution as they allow us to see the small incremental changes that took place over millions of years.
• There are different types of fossils because there are different ways in which fossils can form.
• The most common way that fossils form is by gradual replacement by minerals, as body parts like bones, teeth, and shells decay really slowly, they can be gradually replaced by minerals and form rock-like substances in the exact same shape and size as the original structures.
• The organism remains completely intact and can happen in glaciers where it's too cold for the microorganisms that normally carry out the decay process to survive or in peat bogs where it's too acidic for microorganisms.
• The oldest fossils that we found so far are between three and a half to four billion years old but we don't have a complete fossil record as there are currently big periods where we don't really know what happened and importantly we still don't know how life first developed on earth.
• Many early life forms were soft bodied so they would have decayed really quickly making any fossil remains unlikely.
• Fossils that formed so long ago may have been destroyed in the time since for example by volcanoes earthquakes or perhaps larger geological activity like the movement of tectonic plates.
• A species can be said to have gone extinct when no individuals of that species remain.
• There are absolutely loads of reasons why species might go extinct one of the main ones is that the environment changes too quickly for example if a species habitat all gets cut down or destroyed or if the entire planet gets too warm too quickly or it could be because a new predator arrives and slowly kills them.
• Human hunting has driven entire species to extinction.
• A new species can come along and outcompete existing species for food or some other resource.
• A catastrophic event like the asteroid that hit Mexico and wiped out the dinosaurs 66 million years ago can also cause species to go extinct.
• Another type of fossil is a cast, which is formed when an organism is buried in a soft material like clay, and as the clay hardens, the organism decays, leaving a gap of the same size and shape as the organism was.
• Impressions are another type of fossil, which are things like footprints where organisms leave a mark on the ground that stays there over time.
• Very occasionally, fossils can form by preservation, where no decay happens at all, this happens when organisms get stuck in amber or tar pits, and because there's no oxygen or moisture, no decay can take place.