Earth+History

//**Earth History: **// It is estimated that the Earth formed along with the Solar System 4.6 billion years ago (4600 MYA) Geologic time scale A summary of the major events in Earth's history EON- Largest segment of geoloic times ERA Period EPOCH- Smallest segment of geologic time 

Reading the rock record: Relative Time VS. Absolute Time Places events in Identifies the actual a sequence but dates if geological does not identify events their actual date of occurrence

<span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">**Finding the age of rocks with relative time** <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Law of superposition in undisturbed sedimentary rocks the oldest rock layers are at the bottom and the youngest are at the top. <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Law of cross- cutting relationships- An igneous intrusion is younger than the rock it has intruded into. (look at the whiskers <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Law of included fragments- if fragments of one type of rock are found in another rock layer the rock fragments must be older than the rock layer in which they are found <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Faulted and folded layers- Layers of rock that have been faulted or folded must have been present before the action of faulting or folding took place. <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Unconformaity- A place in the rock record where layers of rock are missing because of uplift and erosion. The result can be a large age difference between the rocks above and those below the erosional surface (it appears like a squiggly line in a cross section <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Rock Correlation: <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">Matching of rock layers that can be seen at the Eath;s surface over a large area <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">An outcrop is exposed rock layers at the earth's surface <span style="color: #ff0099; font-family: Verdana,Geneva,sans-serif;">A key bed is a thin widespread layer usually of volcanic ash that can be used to correlate an exact point of time <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Fossils: <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">A fossil is any evidence of earlier life presevered in the rock <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Original remains: (rare)- the actual unchanged remains of the plant of animal are preserve <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Replaced Remains- the soft parts of the original animal have disappeared and the hard parts have been replaced by mineral material (petrified wood) <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Molds and casts- fossil shells or bones are dissolved completely out of the rock leaving a hollow depression in the rock. New mineral material fills the mold it forms a cast of the original fossil <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Trace fossils- evidence of life other then remains which includes any impressions left in the rock. (trails, footprints,tracks burrows) <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Index fossils: <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Easily identifiable <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Short-lived <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Widespread occurrence <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Measuring Absolute time <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Tree rings <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Each ring represents a single year (spring/fall) the width of the ring depends upon the temperature and rainfall <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Vares <span style="color: #dd00ff; font-family: Verdana,Geneva,sans-serif;">Glacial lake deposits. A thick light colored layer in the summer and a thin dark layer in the winter <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;"> <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Radioactive Dating: <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Used to date far back in time. Certain rocks contain radioactive isotopes <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Radioactive Isotopes are atoms of elements that give off radiation from their nuclei <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Radioactive Decay is the process by which a radioactive isotope changes into a new stable element <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Half-Life <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">the rate at which a radioactive element decays. It is the time it takes for half of the atoms of the radioactive element to decay to a stable end product (see page 1 of the first ESRT) <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">At the end of each half-life half of the radioactive material remains <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Parent isotope= the radioactive isotope that begins <span style="color: #7fb9f5; font-family: Verdana,Geneva,sans-serif;">Daughter Isotope= the stable isotope that has been changed