Biology - Chp 17 - History Of Life - PowerPoint

Chapter17

The History of Life

17-1 The Fossil Record• Studying life’s history is one of the

most fascinating and challenging parts of biology

17-1 The Fossil Record• And researchers go about it in

different ways

Fossils and Ancient Life• From the study of fossils,

Paleontologists infer what past life forms were like and the environment that they lived

• They also classify them and arrange them in the order in which they lived

• Together, all of this information is called The fossil record

What the Fossil Record Shows

• Fossils occur in a particular order• Life has changed over time• More than 99 percent of all

species that have ever lived have become extinct

Extinct• When a species dies out

How Fossils Form• For a fossil to form, either the remains

of the organism or some trace of its presence must be preserved

• The formation of fossils depends on a precise combination of conditions

• Most fossils form in sedimentary rock

Interpreting Fossil Evidence• More often than not, a Paleontologist must

analyze and interpret a fossil from a few fossil bits

• When they study fossils, they look at anatomical similarities and differences between the fossil and living organisms

• Also a fossils age is extremely important• Paleontologists determine the age of a fossil

using 2 techniques

1. Relative Dating• The relative age of a fossil is

determined by comparing its placement with that of fossils in other layers of rock

Index Fossils• Used to compare the relative

ages of fossils

To be used as an index fossil, a species must

1. Be easily recognized2. Existed for a short period of time3. Have a wide geographical range

2. Radioactive dating• Used to determine the absolute

age of rocks using radioactive elements

• Radioactive elements decay or break down into non-radioactive elements at a steady rate

Half life• The length of time required for half

of the radioactive atoms in a sample to decay

• In radioactive dating, scientists calculate the age of a sample based on the amounts of remaining radioactive isotopes it contains

Geologic Time Scale• Paleontologists use divisions of

the Geologic time scale to represent evolutionary time

Eras• Divides the time between the

Precambrian and Present

Periods• Subdivides eras

Cambrian Explosion

Ordovician

Silurian

Devonian

Carboniferous

Permian

Triassic

Jurassic

Cretaceous

Tertiary

Quaternary

What would it take to bring on a new geological era?

1. Change the atmospheres composition, thus modifying plants

2. Change the distribution and diversity of species, thereby changing the future fossil record

3. Acidify the oceans, which will modify the mineral deposits on the ocean floor

• Does this sound familiar?

New era being proposed• “Anthropocene”• New era characterized by the

domination of the planet by one species…us.

17 – 4 Patterns of Evolution• Biologists often use the term

macroevolution to refer to large-scale evolutionary patterns and the processes that occur over long periods of time

Six important topics in macroevolution are

1. Extinction2. Adaptive radiation3. Convergent evolution4. Coevolution5. Punctuated equilibrium6. Changes in developmental genes

Extinction• More than 99% of all species that have

ever lived are now extinct• Usually extinctions happen the way

Darwin proposed• Sometimes mass extinctions wipe out

entire ecosystems• Many times mass extinctions are

followed by a burst of evolution that produces many new species

Adaptive Radiation• When a single species or a small

group of species has evolved into diverse forms that live in different ways

Convergent Evolution• When unrelated organisms come

to resemble one anotherEx.) sharks and dolphins

Q: How does this happen?

A: Adaptive radiation can happen in different places and times but in ecologically similar environments

Analogous Structures• Structures which look and

function similarly but are made up of parts that don’t share a common evolutionary history

Coevolution• The process in which 2 species

evolve in response to changes in each other

Ex.) plants + pollinatorsplants + herbivorous insectsbats + moths

Plants and Pollinators

Hammer Orchid

Bats vs. MothsAn Evolutionary Arms Race

Rough Skinned Newt vs. Garter Snake

Punctuated Equilibrium• There is no question among Biologists that

evolution has happened and is happening today• There are however questions about how fast

evolution happens• Darwin thought that evolution was slow and

steady. He called this idea Gradualism• This idea is supported by fossil evidence• However, the fossil record also shows changes

that have happened over relatively short periods of time (hundred of thousands-even million-of years)

Punctuated Equilibrium• Long stable periods of equilibrium

interrupted by brief periods of more rapid change

• This may be the result of genetic isolation

Developmental Genes and Body Plans

• Biologists have long suspected that changes in the genes for growth and differentiation during embryological development could produce transformations in body size and shape

• Until recently, researchers had only limited ability to affect gene activity in embryos

Developmental Genes and Body Plans

• We can now perform experiments with gene expression by turning genes on or off and examining the results

• Small changes in the timing of cell differentiation and gene expression can make the difference between two completely different phenotypes