Fossils Used as Evolutionary Evidence

Describe the structures of this fossil of an Ichthyosaurus. What do these observations tell you about the life of the organism and the environment during this time? Dolphin like marine reptiles that prowled the seas in the Mesozoic era

GQ: What do we call a scientist who studies fossils? From these fossils they infer what past- life forms were like (structure of the organism, what they ate, what ate them, and the environment in which they lived)

Formation of Fossils Fossils only form in one type of rock: Sedimentary Steps of Formation: 1. Organism Dies (may sink to the bottom of a body of water) 2. Organism is buried in sediment and the sediment builds up until it covers the organism completely *Shells, Bones, Teeth are most likely to become fossils; the are less susceptible to decay than soft tissues

Formation of Fossils Steps of Formation: 3. Minerals replace the organic matter or fill the empty pore spaces or organism decays and leaves behind an imprint of its body 4. Sediments harden into rock *Shells, Bones, Teeth are most likely to become fossils; the are less susceptible to decay than soft tissues

Fossils & Ancient Life Fossils are the most important source of information about extinct species (More than 99% of all species that have ever lived on Earth have became extinct) GQ: What does extinct mean? Fossils that are found are put into groups of similar organisms and they arranged in order in which they lived – from oldest to most recent. This information is called the fossil record. GQ=Group Question

Fossils & Ancient Life Is a fossil record 100% complete? The fossil record is not complete considering some organisms became extinct without leaving a trace GQ=Group Question

Dating Fossils GQ: Predict how you think paleontologists determine how old fossils are? Relative Dating & Radioactive Dating

WHAT ALL COULD THIS TELL YOU? Imagine that you are an investigator and you come across a suspects messy office desk. On the messy desk you find a tea cup on top of a half written essay which is on top of an open geology textbook, which is on top of a birthday card from a friend. At the very bottom of the pile is a graded math test. WHAT ALL COULD THIS TELL YOU? Which happened first? What could you infer about the student’s birthday?

Relative Dating Since sedimentary rock is formed as layers of sediment are laid on top of existing sediments, lower layers of sedimentary rock and fossils they contain are older than upper layers. This allows paleontologists to determine whether a fossils is older or younger than other fossils

Radioactive Dating Relies on radioactive isotopes, which break down, into stable isotopes at a steady rate Half-Life: Time required for half of the radioactive isotope atoms in a sample to decay Carbon-14 is one isotope that is useful in dating fossils