{{Uniformitarianism - the forces and processes that we observe today have been at work for a very long time.{{
Relative dating - tells us the ==sequence in which events occurred==, not how long ago they occurred.
Law of superposition - states that in an ==undeformed sequence of sedimentary rocks==, ==each bed is older than the one above it and younger than the one below i==t.
Principle of Original Horizontality - means that ==layers of sediment are generally deposited in a horizontal position.==
Principle of Cross-Cutting Relationships - states that ==when a fault cuts through rock layers==, or ==when magma intrudes other rocks and crystallizes==, we can assume that the ==fault or intrusion is younger than the rocks affected==.
A ^^disconformity^^ is when two sedimentary rock layers are separated by an erosional surface.
Correlation - is ==establishing the equivalence of rocks of similar age== in different areas.
Fossils - are the ==remains or traces of prehistoric life==. They are ==important components of sediment and sedimentary rocks==.
* The type of fossil that is formed is ==determined by the conditions== under which ==an organism died and how it was buried.==
Unaltered Remains - Some ==remains of organisms==—such as ==teeth==, ==bones==, and ==shells==—==may not have been altered==, or ==may have changed hardly at all over time==.
Indirect Evidence
Conditions favoring Preservation
The principle of fossil succession - states that ==fossil organisms succeed one another== in a ==definite and== ==determinable order==. Therefore, ==any time period can be recognized by its fossil content==.
Index Fossils - are ==widespread geographically==, are ==limited to a short span of geologic time==, and ==occur in large numbers.==
Interpreting Environments - Fossils can also be ==used to interpret and describe ancient environments.==
Basic Atomic Structures
◆ ==Orbiting the nucleus== are ^^electrons^^, which are ==negative electrical charges==.
◆ ^^Atomic number^^ is the ==number of protons== in the atom’s nucleus.
◆ ^^Mass number^^ is the ==number of protons plus the number of neutrons== in an atom’s nucleus.
Radioactivity - is the ==spontaneous decay of certain unstable atomic nuclei==.
Half-life - is the ==amount of time necessary== for ==one-half of the nuclei in a sample to decay to a stable isotope==.
- is the ==procedure of calculating the absolute ages of rocks and minerals== that ==contain radioactive isotopes==.
* Each ^^radioactive isotope^^ has been ==decaying at a constant rate since the formation of the rocks== in which it occurs.
* As a radioactive isotope decays, ==atoms of the daughter product are formed== and accumulate.
* An ^^accurate radiometric date^^ can be ==obtained only if the mineral remained in a closed system== ==during the entire period since its formation.==
Radiocarbon Dating - is the ==method for determining age== by ==comparing the amount== of ==carbon-14== to the amount of ==carbon-12== in a sample.
* When an organism dies, ==the amount of carbon-14 it contains gradually decreases as it decays==. By comparing the ratio of carbon-14 to carbon-12 in a sample, radiocarbon dates can be determined.
* Radiometric dating has supported the ideas of ==James Hutton==, ==Charles Darwin==, ==and others== who inferred that geologic time must be immense.
{{Theme: Evolution drives diversity and unity of life{{
○ It refers to the ==cumulative change in a population of organism over time==
(1830-33)
- revived Hutton's principle of slow geological change, and presented a classic explanation of development over millions of years.
Natural Selection:
Theory of Natural Selection:
{{4 Main Points:{{
{{* Adaption{{
{{* Variation{{
{{* Overproduction{{
{{* Descent/ modification{{
Eons - represent the ==greatest expanses of time==. Eons are divided into ==eras==. Each era is subdivided into ==periods==. Finally, periods are divided into smaller units called ==epochs==.
◆ There are three eras within the ^^Phanerozoic eon^^: the ^^Paleozoic^^, which means ==“ancient life==,” the ^^Mesozoic^^, which means ==“middle life,”== and the ^^Cenozoic^^, which means ==“recent life.”==
◆ Each period within an era is characterized by ==somewhat less profound changes in life forms== as compared with the changes that occur during an era.
◆ The periods of the Cenozoic era are divided into still smaller units called ==epochs==, during which ==even less profound changes in life forms== occur.
- During Precambrian time, there were fewer life forms. ==These life forms are more difficult to identify== and the ==rocks have been disturbed== often.
◆ A ^^sedimentary rock^^ ==may contain particles that contain radioactive isotopes==, but these particles are not the same age as the rock in which they occur.
◆ The age of a particular mineral in a ^^metamorphic rock^^ ==does not necessarily represent the time when the rock was first formed==. Instead, the ==date may indicate when the rock was metamorphosed==.
- The Precambrian ==encompasses immense geological time==, from Earth’s distant beginnings 4.56 billion years ago until the start of the Cambrian period, over 4 billion years later.
Precambrian Rocks:
• ^^Shields^^ are large, relatively flat expanses of ancient metamorphic rock within the stable continental interior. • Much of what we know about ==Precambrian rocks comes from ores mined from shields==.
Earth’s Atmosphere Evolves
• Earth’s original atmosphere was made up of gases similar to those released in volcanic eruptions today—water vapor, carbon dioxide, nitrogen, and several trace gases, but no oxygen.
• Later, primary plants evolved that used photosynthesis and released oxygen.
• Oxygen began to accumulate in the atmosphere about 2.5 billion years ago.
Stromatolites - The most common fossils. They are ==distinctively layered mounds or columns of calcium carbonate==. They are ==not the remains of actual organisms== but are the ==material deposited by algae==.
* Many of these ancient fossils are preserved in ^^chert^^—==a hard dense chemical sedimentary rock==.
Following the long Precambrian, the most recent ==540 million years== of Earth’s history are divided into three eras: ==Paleozoic, Mesozoic, and Cenozoic.==
• During the Cambrian, Ordovician, and Silurian periods, the vast southern continent of ^^Gondwana^^ encompassed five continents (South America, Africa, Australia, Antarctica, and part of Asia).
• Life in early Paleozoic time was restricted to the seas.
Laurasia - is the ==continental mass== that formed the northern portion of Pangaea, consisting of present-day North America and Eurasia.
* By the end of the Paleozoic, all the continents had fused into the supercontinent of ==Pangaea==.
• Some ==400 million years ago,== plants that had adapted to survive at the water’s edge began to move inland, becoming ==land plants==.
• The ^^amphibians^^ rapidly diversified because they had minimal competition from other land dwellers.
◆ The world’s ==climate became very seasonal==, probably ==causing the dramatic extinction of many species==.
◆ The late Paleozoic extinction was the ==greatest of at least five mass extinctions to occur over the past 500 million years.==
◆ Dinosaurs were land-dwelling reptiles that thrived during the Mesozoic era.
Mesozoic History
• A major event of the Mesozoic era was the breakup of Pangaea.
Mesozoic Life
• ^^Gymnosperms^^ are ==seed-bearing plants that do not depend on free-standing water== for fertilization.
• The gymnosperms quickly became the ==dominant plants== of the Mesozoic era.
• Unlike amphibians, ==reptiles have shell-covered eggs== that can be laid on the land.
• The ==elimination of a water-dwelling stage== (like the tadpole stage in frogs) was an i==mportant evolutionary step.==
Reptiles Dominate
• With the perfection of the shelled egg, ==reptiles quickly became the dominant land animals==.
• ==At the end of the Mesozoic era==, many ==reptile groups became extinct==.
◆ The ^^Cenozoic era^^ is divided into two periods of very unequal duration, the ==Tertiary period== and the ==Quaternary period==.
◆ ^^Plate interactions^^ during the Cenozoic era caused many events of ==mountain building==, ==volcanism==, and ==earthquakes== in the West.
Cenozoic Life
Mammals - ==animals that bear live young== and maintain a steady body temperature— ==replaced reptiles as the dominant land animals== in the Cenozoic era.
Angiosperms - ==flowering plants with covered seeds==—replaced gymnosperms as the dominant land plants.
Mammals Replace Reptiles
• Adaptations like being warm blooded, developing insulating body hair, and having more efficient heart and lungs allow mammals to lead more active lives than reptiles.
Large Mammals and Extinction
• In North America, the mastodon and mammoth, both huge relatives of the elephant, ==became extinct==. In addition, saber-toothed cats, giant beavers, large ground sloths, horses, camels, giant bison, and others died out on the North American continent.
• The reason for this recent wave of extinctions puzzles scientists.