Chapter 12 History of Life

Fossil Record• Fossils – preserved form of ancient life

- can be found in ancient rocks, petrified tree sap, peat bogs, tar pits, and polar glaciers• Fossil record – grouping of similar organisms

and arranging them in order in which they lived – oldest to most recent

- provides evidence about history of life on Earth and how different groups changed over time

Fossil Record• Paleontologists are scientists who study fossils

- compare anatomical similarities to present day living organisms - try to sequence the age based on location

in the rock layers• Its believed that 99% of all species have become

extinct or died out over course of Earth’s history

Fossil Formation• Most fossils form in

sedimentary rock• conditions deteriorate

other rock layers into small particles that then carried to other locations and settle into sediment layers

• Sediments are compressed together preserving intact organisms within layers

Dating FossilsTwo ways of determining age:

1. Relative dating – determines age of fossil by comparison of its placement with fossils in other rock layers.

- rock layers form in order by age where oldest is at the bottom and youngest near the surface

2. Radioactive dating – uses the half life of radioactive elements to predict absolute age

- elements decay at a certain rate; when half of the sample remains, that is the half life

Ex: carbon 14(radioactive isotope)

Geologic Time• Used to represent evolutionary time• Combines worldwide index fossils; and rock layers,

relative age of rock layers• Radioactive dating has sequence ages that vary in

millions of years• Segments have 3 major divisions:

1. Precambrian time2. Eras – Paleozoic, Mesozoic, and Cenozoic3. Periods – Mesozoic Era- Triassic- Jurassic- Cretaceous

Earth’s Early History

• Earth’s origin is believed to be 4.6 billion years old

• Conditions and contents of chemicals were quite different from today

Ex: atmosphere was possibly made up of hydrogen cyanide, CO2, CO, H2SO3,

Nitrogen, and water• Volcanic eruptions, comet and asteroid

collisions, and lack of oceans

First Organic Molecules

• 1950’s scientists Stanley Miller and Harold Urey ran experiments to find out if organic molecules could have formed under harsh conditions of the infant planet Earth

- filled flask with hydrogen, methane, ammonia and water to simulate the atmosphere and passed electric current through the mixture

-over days they produced several amino acids

Life’s Origin• Under certain conditions large organic

molecules can form tiny bubbles called proteinoid microspheres

- not cells but resemble living systems- membranes, stores and releases energy- evolved to modern form of cell

• RNA may have formed before DNA and given rise to the evolution of DNA

Free Oxygen

• Microfossils resembled the first single celled prokaryotes that changed to modern bacteria

• They evolved without oxygen and over time became photosynthetic

• Oxygen combined with iron in the oceans making them orange

• Increase in oxygen served as pollutant to the Earth and may be to blame for extinction of some life forms; while others evolved

First Eukaryotes• Possible origins of a nucleus containing cell began 2

billion years ago• The Endosymbiotic theory proposes that eukaryotic

cells arose from living communities formed by prokaryotic organisms

- mitochondria and chloroplast make the main connection to theory- both have DNA- both have ribosomes- both can reproduce by binary fission

Patterns of Evolution

• Macroevolution – large scale evolutionary patterns and processes, beyond a single species, that occur over long periods of time

• Six patterns of macroevolution are:1. Extinction2. Adaptive radiation3. Convergent evolution 4. Coevolution5. Punctuated equilibrium6. changes in developmental genes

Extinction• What are the events that led to extinction of species?• What separates mass extinctions from extinction itself?

• Competition for resources and environmental change, lack of adaptations ( or Natural selection itself) can explain some extinctions.

• Mass extinctions were usually occurred because food webs collapsed, energy flow was disrupted, and basically the environment is collapsing around the organisms.

Ex: Massive asteroids collisions, shifting continents, changes in sea level

Adaptive Radiation• Evolution of many diversely adapted

species from a common ancestor after being introduced into new environmental opportunities and challenges

• Changes in environment can cause the progression and divergence toward dominant species in the ecosystem;

• Extinction clears the way other species to become more prominent and diverge

Convergent Evolution• Process where unrelated organisms come to

resemble one another- caused with different species undergo

adaptive radiation to similar environmental conditions- organisms have different ancestral species but

same demands of the environment- Analogous structures - structures of the body

between two species have similar appearance and function, but have different parts and different evolutionary history

Ex: bee wings vs. hummingbird wings

Coevolution

• Process where two species evolve in response to changes in each other over time

- usually two closely connected species that have frequent ecological interactions

Ex: flowering plants and their pollinators

Punctuated Equilibrium

• Punctuated equilibrium – episodes in fossil record where a new species suddenly appeared, persisted unchanged, and then disappear

- Time period of the fossil record skews the perception of changes that occurred making them unnoticeable

- long stable periods interrupted by rapid change

Developmental Genes

• Controlling gene expression by turning genes “on or off” can dramatically effect the growth and differentiation of embryonic cells

Ex: hox genes control orientation of body parts- small changes in control genes can have large impact on adult organisms- sheds new light on evolutionary

transformation of species