{ Looking at Fossils Chapter 2.1. If the half-life of Uranium-232 is 70 years, how many half lives...
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Transcript of { Looking at Fossils Chapter 2.1. If the half-life of Uranium-232 is 70 years, how many half lives...
If the half-life of Uranium-232 is 70 years, how many half lives will it take for 10g to be reduced to 1.25g?
Mercury-197 is used for kidney scans and has a half life of 3 days. If the 32g of Mercury-197 is ordered, but takes 15 days to arrive, how much would arrive in the shipment?
Is radioactivity an example of relative or absolute dating? Why?
Warm-up
The remains or traces of physical evidence of an organisms preserved by key geologic processes is called a fossil.
Fossils are important because they give us clues about the past
Most fossils are hardened animal remains such as shells, bones, teeth, and skeletal body parts
Other fossils are impressions or preserved organisms found in rock
Looking at Fossils
1. Conditions have to be just right for fossils to from in rock
2. Organisms must be preserved before it decomposes or disappears
Usually soft parts decays too fast, which is why fossils only really show hard parts of plants and animals
3. Fossils form in the layers of sedimentary rock
So How Are Fossils Formed
Fossils that are the actual bodies or body parts of organisms are called original remains
Original remains are found in places where conditions prevent the decomposition or breakdown to occur
Original Remains
1. Ice – best preserver of prehistoric life. Ice has preserved original remains of things such as a 10,000 year old mammoth which have been found with bones, muscles, skin, and hair still in place
2. Amber – formed from the sticky substance inside trees that flows like syrup. If an insect is caught in the sap, the sap will cover the insects entire body and harden.
3. Tar – thick, oily pool of liquid. Things such as saber toothed cats and other animals were trapped and preserved
Types of Original Remains
If an organism is caused by or buried in sediment it may become a rock
Some fossils are not original remains or actual body parts, instead they are impressions or traces made in rock.
Fossils in Rocks
Molds and Casts:
A mold is a visible shape that was left after an animal or plant was buried in sediment and then decayed away.
A cast is an object that is created when sediment fills a mold and becomes rock.
Types of Rocks
Petrification
The process in which minerals pass through and replace the organisms cells with minerals which produces a stone-likeness to the object. Commonly happens with trees that die and are covered in sediment
Carbon Films
Carbon is found in every living thing. Sometimes when a dead plant or animal decays, a visible carbon layer is left behind. These show the soft parts of these organisms that are rarely seen in other fossilsTypes of Rocks
Trace Fossils
Preserved evidence of animal activity or movement
Examples: Tracks – which tells us the size of animal and
speed Burrows – shelters made by animals buried in
sediment Feces – preserved animal poop
Types of Rocks
Index fossils lived in many areas but only existed during specific time spans
These characteristics make it extremely helpful when trying to date the age of a specific rock layer.
Special Type of Fossils
Activity # 1 Obtain Set A materials: 8 index cards or slips of paper with letters on them.
Each slip of paper represents a rock layer.
Each letter represents a kind of fossil.
Your task is to determine what the correct sequence of the letters are, from oldest to youngest.
Questions:
1. What letter is the oldest?2. What letter is the youngest?3. What letter showed up the most?4. Which letters only showed up
once?5. Which letters could be index
fossils?6. How did you know which was
older: “M” or “X”?
Ice core video
http://teachertube.com/viewVideo.php?video_id=240111
So what do they tell? • One big thing they tell us is the connection between CO2 and climate long time ago.
• When looking at ice core samples, scientist use bubbles of past atmosphere as indicators of past life.
• This helps us analyze and determine past levels of greenhouse gases, which helps us understand temperature