THE HISTORY OF LIFESC STANDARD B-5 Students will demonstrate an

understanding of the basis of evolution

CN: page 54 notebookTopic: The History of LifeEQ: What are the 4 important

patterns of macroevolution?

FOSSILS

Paleontologist: scientists who study fossils

Fossil Record: information about past life, including the structure of organisms, what they ate, in what environment they lived, & order in which they lived

This species lived 7700 years ago

The fossil record provides evidence about the history of life on Earth.

It also shows how different groups of organisms, have changed over time.

Extinct: term used to describe a species that has died out

Lists of Extinct Animals

http://extinctanimal.com/extinct/extinct_mammals.htm

How Fossils Form

Formation of any fossil depends on a precise combination of conditions

Evolution of Whales

Why is the fossil record described as an incomplete record of life’s history?

Interpreting Fossil Evidence

Erosive forces cut through sedimentary rock wearing away the youngest layers first, exposing any fossils embedded in them.

Paleontologists reconstruct extinct species from few fossil bits to entire bodies. They look for similarities & differences with living organisms

Relative Dating

In relative dating, the age of a fossil is determined by comparing its placement in the layers of sedimentary rock

Relative Dating

Index fossils: distinctive fossil used to compare relative ages of fossils

Radioactive Dating

half-life: is the length of time required for 50% of the sample of radioisotopes to decay

radioactive dating: calculating the age of a fossil based on the remaining radioactive isotopes◦assumption is: the amount of C-14, for example, has remained constant

◦C-14 can only be used for fossils <60,000 yrs because of its short half-life (not enough specimen left to measure)

Radioactive Decay of K-40

Geologic Time Scale

Formation of Earth

Geologic evidence suggests that Earth formed over millions of years

Process began ~4.6 billion years ago

This process involved multiple collisions and temperatures so high anything solid melted

While melted substances arranged themselves by densities

Less dense substances floated to surface and gradually cooled forming Earth’s crust

Earth’s Early Atmosphere

Hydrogen & Nitrogen formed early atmosphere◦hydrogen cyanide◦carbon dioxide◦carbon monoxide◦sulfide◦water

~ 4 billion years ago Earth had cooled enough to allow 1st solid rocks to form

still being bombarded by comets, asteroids, etc.

too hot for water to exist in liquid form

~ 3.8 billion years ago Earth’s surface cooled down enough for water to stay in liquid phase

Oceans covered most of planet◦Oceans brown due to

dissolved iron◦Oldest sedimentary

rock deposited in water

The 1st Organic Molecules

Miller & Urey tried to reproduce conditions on early Earth in a lab:

CH4 , H2 , NH3 , H2O in a flask to represent early atmosphere

passed electric shocks through it to simulate lightening

Over a few days several amino acids began to accumulate

Results suggests how mixtures of organic cpds necessary for life could have arisen from simpler cpds present on primitive Earth

Endosymbiotic Theory

Proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms◦Mitochondria◦Chloroplasts