THE HISTORY OF LIFE SC STANDARD B-5 Students will demonstrate an understanding of the basis of evolution

CN: page 54 notebook Topic: The History of Life EQ: 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 FOSSILS

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 This species lived 7700 years ago

Lists of Extinct Animals http://extinctanimal.com/extinct/extinct_mammals.htm Lists of Extinct Animals

Formation of any fossil depends on a precise combination of conditions How Fossils Form

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

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

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

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

Relative Dating

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

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 Dating

Radioactive Decay of K-40

Geologic Time Scale

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 Formation of Earth

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 Earth’s Early Atmosphere

Oceans covered most of planet ~ 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 The 1st Organic Molecules

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