8 - Unit 5, Section 1

Fossils

Unit 5, Section 1

What clues did you use to come to your conclusion?

How accurate do you think you could be?

When Was This Picture Taken?

Fossils

• Fossil - the preserved remains or evidence of ancient organisms

• Fossils can provide information about ancient plants and animals

  • What they looked like

  • What they ate

  • How they moved

  • How they died

Open Ended

Define "catastrophe" in your own words.

• Catastrophism - the idea that the conditions and organisms on Earth change in quick, violent events

• It views Earth's history as a series of disasters that happen over a short period of time

• It's used to explain why there are so many fossils of plant and animal species that are extinct

Catastrophism

The Problem With Catastrophism

• Most supporters of catastrophism believed Earth was only a few thousand years old

• James Hutton - a farmer that observed how his property changed over time by erosion and weathering

  • He hypothesized that Earth could be changed by the same forces, but that it would take much longer than a few thousand years

• His ideas became the foundation of uniformitarianism

Uniformitarianism

• Uniformitarianism - the hypothesis that the geologic processes that occur today are similar to those that have occurred in the past

• Earth's surface is constantly being reshaped in a steady, uniform manner

• This doesn't rule out catastrophes, it just states that catastrophes are not the main way Earth's surface changes

Open Ended

Think-Pair-Share: work with your nearest neighbor and use your Chromebook to determine the conditions under which fossils form.

Conditions For Fossil Formation

• Most organic matter (for example, an apple) will decay long before it can become a fossil

• Organisms with hard parts (shells, teeth, bones, etc.) are more likely to become fossils

• These parts decay slowly

• Organisms that are quickly buried under sand, soil, mud, or tar are more likely to become fossils

• They are cut off from airborne bacteria which would decompose them

• There are 6 types of fossils:

  • Preserved Remains

  • Carbon Films

  • Mineral Replacement Fossils

  • Molds

  • Casts

  • Trace Fossils

Types of Fossils

​Fossil Sizes

​Fossils can be microscopic, to representing the largest animals that ever lived.

• Preserved Remains - an intact, or mostly-intact, organism

• It must have been completely enclosed in a material (closed off from air and bacteria)

  • Ice

  • Peat

  • Tar

  • Amber

• Generally, preserved remains are less than 10,000 years old

Preserved Remains

• Carbon Film - the fossilized carbon outline of an organism or part of an organism

• Formed when heat and pressure force gas and liquids out of an organism, leaving only the carbon behind

Carbon Films

• Mineral Replacement - minerals from groundwater collect and replace the tissue of dead organisms

• Forms a replica (copy) of the organism

• Petrified wood is the most common example

Mineral Replacement

• Mold - the impression in a rock left by an ancient organism

• Formed when sediment hardens around a buried organism

• The organism decays, leaving the mold behind

• The sediment eventually turns into rock

Molds

• Cast - a full copy of an organism made when a mold is filled with sediment or mineral deposits

• Only the exterior of the organism is copied

• Animals with shells often formed casts

Casts

• Trace Fossil - the preserved evidence of the activity of an organism

• Trace fossils include tracks, footprints, and nests

• They help scientists learn about the characteristics and behaviors of ancient animals

Trace Fossils

• Paleontologists - scientists who study fossils

• They use uniformitarianism and fossils to learn about ancient organisms and their environments

Ancient Environments

• From the late Cretaceous period to the early Paleogene period (100-65 millions of years ago, or mya), a large portion of North America was covered by a shallow sea

• We know this because we've found the fossils of aquatic plants and animals in the middle of the continent

Shallow Seas

Multiple Choice

This type of fossil is formed when an organism is buried and cut off from air and bacteria.

• Preserved Remains

• Mineral Replacement Fossil

• Mold

• Cast

Multiple Choice

The preserved footprints of a stegosaurus is an example of this type of fossil.

• Mold

• Trace Fossil

• Cast

• Preserved Remains

Multiple Choice

This type of fossil is formed when the organic material of an organism is slowly replaced by minerals that have been dissolved from groundwater.

• Preserved Remains

• Mineral Replacement Fossil

• Carbon Film

• Trace Fossil

Multiple Choice

The replica of an organism that is formed when sediment fills a mold is this type of fossil.

• Cast

• Mold

• Mineral Replacement Fossil

• Carbon FIlm

Multiple Choice

If a fern dies, is buried by sediment, and has all of its liquids and gases pushed out due to pressure, it will form this type of fossil.

• Mineral Replacement Fossil

• Mold

• Carbon Film

• Cast

Multiple Choice

The impression left, in rock, by an ancient organism is an example of this type of fossil.

• Cast

• Mineral Replacement Fossil

• Carbon Film

• Mold

Past Climates

• The fossil record shows that Earth goes through periods of warming and cooling

  • Fern fossils = warm, tropical climate

  • Mastodons and grasses = cool, arctic climate

• We know this because we can determine the age of fossils