Chapter 7

The Evolution of Living Things

Diatryma and the Rooster

• Diatryma weighed about 400 pounds (182 kg.)

• Flightless• Cenozoic Era (57-35) million

years ago• Over 6 feet tall• Enormous Beak• Sharp Claws• Distant relative of the chicken

Frog Crazy

Adaptation

Adaptation – a characteristic that helps an organism survive and reproduce in its environment

Adaptations Include Structures and Behaviors for:

1) finding food

2) protection

3) moving from place to place

Species

Species – a group of organisms that can mate with one another to produce fertile offspring

Do Species Change over Time?• Millions of different species occupy the Earth, ranging

from bacteria to fungi to plants and animals.

• Have these same species always existed on Earth?

The Earth is 4.6 Billion Years Old

• Over that period of time the Earth has changed dramatically.

Human existence is less than a hairs width at the end of the diagram

• Radioactive Decay of Earth’s Rocks

• Moon Rocks

• Meteorites

How do we estimate the age of the Earth?

• Radiometric Dating of Earth’s Rocks- The ages of Earth rocks are measured by the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements. Used to measure the last time that the rock being dated was melted.

Moon Dating• The Moon is a more primitive planet than Earth because it has not been disturbed by plate tectonics; thus, some of its more ancient rocks are more plentiful. Only a small number of rocks were returned to Earth by the six Apollo and three Luna missions. These rocks vary greatly in age, a reflection of their different ages of formation and their subsequent histories. The oldest dated moon rocks, however, have ages between 4.4 and 4.5 billion years and provide a minimum age for the formation of our nearest planetary neighbor.

Meteorite Dating

• Thousands of meteorites, which are fragments of asteroids that

fall to Earth, have been recovered. These primitive objects provide the best ages for the time of formation of the Solar System. There are more than 70 meteorites, of different types, whose ages have been measured using radiometric dating techniques. The results show that the meteorites, and therefore the Solar System, formed between 4.53 and 4.58 billion years ago.

• The best age for the Earth comes not from dating individual rocks but by considering the Earth and meteorites as part of the same evolving system

Evidence for an old universe:Absence of short lived stars from star clusters 14-18 Ga1

Length it takes light to get to the earth from the most distant objects in the universe (10 Ga)2

Hubble expansion of the universe 7 - 20 Ga1

Evidence for an old solar systemAge of meteorites 4.4-4.6 Ga (isochron method)1

Age of moon 4.5 Ga (radiometric)1 Earth-meteorite system 4.54 Ga (lead isotope age)1

Evidence for an old earth:Earths oldest rocks 3.8-3.9 Ga (radiometric)1

Evolution

Evolution – the process by which populations accumulate inherited changes over time.

* Because of evolution scientists think that all living things and once living things, from daisies to crocodiles to humans share a common ancestor.

The Evidence for Evolution

• Comparative Anatomy – comparing similar structures in different organisms.

• Fossils – the solidified remains or imprints of once living organisms.

• Embryonic Anatomy• Vestigial Structures

– The fossil record –provides a historical sequence of evolution and life.

Fossilization• Paleontology - the study

of the past through the study of fossils.

The fossil is a rock - Often the remains of preserved organisms are not of the organism itself but instead of minerals deposited where, especially, hard parts of the organism previously existed.

Soft parts tend not to fossilize because they usually decay prior to mineralization.

However, soft parts, under the right conditions, can also make impressions. Included among such imprints are those made during the act of locomotion such as fossil foot prints or various invertebrate trails

A once living organism The organism dies The organism is quicklycovered in sediment

The soft parts decay The hard parts make amold (hollow impression)which is replaced by minerals

There are six ways that organisms can turn into fossils, including:

1) unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree sap)

2) permineralization=petrification (in which rock-like minerals seep in slowly and replace the original organic tissues, forming a rock-like fossil - can preserve hard and soft parts - most bone and wood fossils are permineralized)

3) replacement (An organism's hard parts dissolve and are replaced by other minerals.

4) carbonization=coalification5) recrystalization6) authigenic preservation

Most animals did not fossilize; they simply decayed and were lost from the fossil record. Paleontologists estimate that only a small percentage of the dinosaur genera that ever lived have been or will be found as fossils.

Ways of Dating Fossils

• Relative Dating

• Direct Dating

• Relative dating

Uses sediment positional information – the relative positionsof layers of sediment determine the age of the fossils found within them.

• Crucial assumptions:

– older layers are buried beneath younger layers (unless the rock itself has been flipped by geologic forces)

– fossils are found within the layer that formed contemporaneously with the death of the fossilized organism (an assumption which is obviously not necessarily true for organisms which tend to burrow in sediment)

Direct dating • Radioisotope clocks:

– Carbon 14 dating

Non-radioisotope methods of direct dating: – Other methods of direct dating include:

» tree ring comparisons » magnetic alignment with the earth's magnetic pole (which

tends to switch from North to South from time to time; known as paleomagnitism)