Fossils & Geologic Time

Mrs. Wisher

WRITE EVERYTHING IN YELLOW!!

What Are Fossils?

• Fossils are formed when living things die and are trapped in sediments and become rocks

• Petrified fossils are where minerals replace all or part of an organism

• Trace fossils provide evidence of the activities of organisms

Dating Fossils

• Relative age dating – compares their age to age of other rocks

• Absolute age dating – tells their age in years by looking at the decay of isotopes

Relative Dating

Preserved Remains

• Real parts of real organisms that have not changed– Wooly Mammoth

in ice or tar– Insects in amber– Mummified

remains

Preserved Remains

• Long before white men came, Indians knew of and worked in Mammoth Cave in KY. In 1935 two guides exploring found a mummy high on a ledge. From its position and the articles found with it, archeologists pieced together the story. An Indian miner was digging for something in sand on the ledge. A rock above slipped and pinned him down. The body, found many centuries later in an excellent state of preservation, was clad in a breech clout, woven of fiber. Crude stone implements lay nearby.. Close by bundles of reeds, thrust into the sand with singed ends indicated he was using them as a torch. The mummy was found three miles from the nearest natural entrance—three miles of pitch black darkness, lighted for that long-ago miner only by the reed torches he carried. Today the mummy rests in an air-tight glass case just below the ledge on which it was found.

QUESTIONS

• Students at “B” seats – close your notebook and teach your table the difference between relative and absolute dating.

QUESTIONS

• Students at “B” seats – close your notebook and teach your table the difference between relative and absolute dating.

• Relative dating is using the position of the rock layers to determine which is youngest or oldest. Absolute dating gives you a time frame of age based on radioactive decay.

Molds & Casts

• Mold – an impression of the organism

• Cast – an object formed when a mold is filled with sediment

Geological Time Scale

• Why use geological time?

• Earth is about 4.6 billion years old

• Modern humans have only been here less than 100,000 years or less than 1% of Earth’s history.

Geologic Time Scale

– Eras – geological history is divided into 4 eras– Periods – each era is divided into periods

• What 3 periods make up the Mesozoic era?

– Epochs – each period is subdivided into an epoch

• Only the Cenozoic (or most recent) era is divided into epochs. Can you think of why?

Precambrian Era

• Early bacteria and algae form

• First sedimentary rocks appear

• First multicellular organisms develop late in Precambrian.

Phanerozoic Eon – “visible life”

• 1. Paleozoic Era (old life)

• 2. Mesozoic Era (middle life)

• 3. Cenozoic Era (recent life)

Paleozoic Era

• 570 mya to 225 mya

• Trilobites were common animals

• Life explodes during the Paleozoic

• Land plants appeared in middle Paleozoic.

• “Age of the Fish”, all animal life is in the sea - sharks, rays, and bony fish existed.

Paleozoic Era

• Tropical jungle like forest were prevalent by the end of the era.

• Insects (some huge) were the predominant animals.

• Reptiles evolved during the late Carboniferous period

• A mass extinction at the end of the Paleozoic wiped out 95% of all life

Mesozoic Era

• 225 mya – 65 mya• “Age of the Reptiles”• Dinosaurs roamed

Earth.• Pangaea breaks up

during the Jurassic period and is in the present position by the late Cretaceous period

Mesozoic Era

• Birds and mammals started evolving during the last part of the Mesozoic.

• Widespread volcanic activity occurs

• Mass extinction at the K-T boundary is supported by the fossil record

Cenozoic Era

• Recent Life (65 mya to present)• Divided into the Tertiary & Quaternary

period• “Age of mammals”• Ice Age began 3 mya (on New Year’s Eve.)• Took 75000 years to form, stayed 10000

years, then retreated.

Cenozoic Era

• Early animals could be much different than their modern versions.

• Early horses were much smaller and had toes.

Questions?

• Discuss with your shoulder partner, why do you believe that each of the Era’s ended at the time frame that they ended.

Questions?

• Discuss with your shoulder partner, why do you believe that each of the Era’s ended at the time frame that they ended.

• Each of the Era’s (except the Cenozoic which we are still in) ended with a mass extinction event.

Age of Man

• Man evolved at 10:30 pm on New Year’s Eve.• Hominids evolved during the Quaternary period• Australopithecus, the earliest ancestor, evolved

around 3 million years ago• Early hominids include Homo erectus, habilis, and

neanderthalensis• Homo Sapian sapian is the modern man

Homo Neanderthalensis

Otzi the Iceman