Chapter 17: History of Life

Fossil record 1. Provides evidence about the history of life on Earth 2. Includes information about structure of organisms, what they ate, what ate them, and what environment they lived in 3. Shows how species have changed over time. 4. Provides incomplete information about the history of life. 5. Over 99% of all species that have lived on Earth have become extinct.

How Fossils Form Most fossils form in sedimentary rock. Sedimentary rock forms when rock breaks down into small particles of sand, silt, and clay. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may be later discovered and studied.

Relative dating (law of superposition)- Age of a fossil is determined by placement in different layers. Older fossils found beneath newer fossils. The law allows us to determine age of fossils in relation to other fossils but can’t determine the actual age of the fossil.

QUESTION What assumption do paleontologists make when they use relative dating to estimate the ages of fossils? They assume fossils found in the upper layers of sed. rock are younger than fossils found in the lower layers of rock.

Half-life – the length of time required for half of the radioactive atoms in a sample to decay. EXAMPLE: Two Common Radioactive Isotopes: Potassium-40 (half-life = 1.3 billion years) Carbon-14 (half-life = 5730 years) Carbon 12 doesn’t decay so they compare 14 to 12 the more 12 there is compared to 14 the older the sample is.

How long is the half life for carbon 14?

Can assign absolute age of fossils. Radioactive Dating- Use of half lives to determine the age of a sample. Can assign absolute age of fossils. Scientist calculate the age of a fossil based on the amount of remaining radioactive isotopes it contains. Example: Carbon-14 begins to decay when an organism dies. Carbon 12 doesn’t decay so scientist compare 14 to 12 the more 12 there is compared to 14 the older the sample is

1. How many years does it take potassium 40 to reach its half life? Example: Graph – Radioactive Decay of Potassium-40 1. 1.3 billion years 2. It is decreasing by half of an ever smaller amount. 3. 1/32 1. How many years does it take potassium 40 to reach its half life? 2. Why does the curve fall steeply and then start to level out? 3. What fraction of potassium 40 will be present after five half- lives?

1.The fossil record consistently shows evidence that all forms of life have existed in all geologic eras. living organisms have only been on Earth for a short time. living things have changed over time. ancient life-forms are much the same as forms found living today.

2.Determining the age of a fossil by comparing its placement with fossils in other layers of rock is called carbon-14 dating. fossil-indexing. relative dating. absolute dating.

What is the name of the earliest era in geologic time? What are the periods of the Paleozoic Era from oldest to youngest? When did the Cretaceous Period end? Which era and period do we live in?

Earth is thought to have formed about 4.6 billion years ago Formation of Earth Earth is thought to have formed about 4.6 billion years ago 3.5 billion years ago the first living organisms appeared in the ocean Leave blanks

Endosymbiotic theory- Proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Bacteria engulfed lots of other bacteria became organelles (chloroplast and mitochondria) each had their own DNA became unicellular Eukaryotic cells overtime became complex multicellular Eukaryotic cells

Miller and Urey Experiment Miller and Urey produced amino acids, needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. Suggests how simple compounds found on early Earth could have combined to form the organic compounds needed for life.

Miller and Urey Experiment How cells formed Miller and Urey Experiment Energy from sun and lightening triggered chemical reactions to produce simple organic compounds Passed sparks through mixture of the below chemicals Atmosphere contained hydrogen, methane, ammonium and water vapors Used hydrogen, methane, ammonia, and water Simple organic compounds link together to form small proteins Made amino acids that made proteins The first life forms were probably prokaryotes that were anaerobic (no oxygen) Suggest how simple compounds could have combined to form organic compounds needed for life Leave blanks