THE HISTORY OF LIFE

Chapter 17

17-1 THE FOSSIL RECORD

I. FOSSILS AND ANCIENT LIFE

1. Paleontologists- scientists who collect and study fossils

2. Fossil Record- evidence about the history of life on Earth & shows how species have changed over time.

3. Fossils are :a) Classified by

organismsb) Similar fossils are

grouped together in the order in which they lived; from oldest to most recent

c) To tell scientists what the past life form was like, what they ate, the environment they lived in, & what ate them.

4. Extinct- a species died out

5. The fossil record incomplete

6. Over 99% of all species that have ever lived on Earth are now extinct.

All of these whale ancestors are now extinct

II. HOW FOSSILS FORM

1. Fossil formation starts with preserved remains or some trace of the animals presence is preserved.

2. Most fossils form in sedimentary rock

3. Sedimentary rock forms from existing rock being eroded by rain, wind, heat, and cold breaking the rock apart.

a)

b)

c)

III. INTERPRETING FOSSIL EVIDENCE

University of Florida researchers have discovered a 10-million-year-old Neotropical nursery area for the extinct megalodon shark in Panama, providing fossil evidence the fish used these areas to protect their young for millions of years

1. Paleontologists determine the age of fossils using relative dating or radioactive dating

2. Relative Dating- a fossil’s age is determined by comparing it’s placement w/ that of fossils in other areas of layers of rock.

3. Allows paleontologists to estimate the relative age, not the absolute age of a fossil compared with that of the other fossils

3. Index fossils- a species that is recognizable and that existed for a short period but are found in many parts of the world.

4. Index fossils are used to compare relative ages of fossils

The fossils at layers 6, 4, and 3 serve as index fossils to help us understand that these fossils were formed around the same period of time even though they are found in different sediment types and in different places.

5. Radioactive decay can be used to assign an absolute age to rocks

6. Some elements are radioactive & steadily break down into nonradioactive elements

Uranium-238 takes 4.5 billion years to decay to lead, which is a stable product.

7. Radioactive Dating – half-lives are used to calculate the absolute age of a sample based on the amount of remaining radioactive isotopes it contains.

8. Half-life - is the length of time required for half of the radioactive atoms in a sample to decay.

-1st half-life, half of the sample has decayed the other half has not-2nd half-life, 3/4th of the sample has decayed 1/4th has not-3rd half-life most of the sample has decayed except 1/8th of the sample has not decayed

a) Carbon-14 begins to decay when an organism dies.

b) Carbon-12 is not radioactive and does not decay.

c) By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived.

DISCUSS W/ PARTNER: What information do relative dating and

radioactive dating provide about fossils?

ANSWER: The age of a fossil in comparison to

other fossils The age of a fossil based on the amount

of remaining radioactive isotopes it contains.

IV: GEOLOGIC TIME SCALE

1. Geologic Time Scale (GTS)- represents evolutionary time

2. Eras- The time between Precambrian and the present

3. Eras are divided into periods.

3. Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history.

4. The time b/w the Precambrian time and the present into three eras:

a) Paleozoic Erab) Mesozoic Erac) Cenozoic Era

DISCUSS W/ PARTNER: What are the main divisions of the

geologic time scale?

ANSWER: Eras and Periods

5. The Paleozoic Era:

a) Started about 544 million years ago (mya)

b) Last 300 million years

c) Invertebrates (animals w/o backbones) and vertebrates lived during this time

6. The Mesozoic Era:

a) Began about 250 mya

b) Lasted about 280 million years

c) Dinosaurs and other reptiles dominated

d) Mammals began to evolve

7. Cenozoic Era:a) Began about

65 mya to the present

b) Mammals became more common

c) Humans evolved during this time

8. Periods- a unit of time in which Eras are subdivided

9. Periods range in length from tens of millions of years to less than two million years.

10. Many periods are named for places around the world where geologists first discovered the rocks and fossils of that period.