Geologic Time

Earth is about 4.6 billion years old no life for about the first two billion years bacteria were first life to appear no oxygen in atmosphere for the next 1-2 billion years when oxygen was in the atmosphere, life began to flourish Homo sapiens only here for about 200,000 years

What is the Earth’s time scale? The Geological time scale is a record of the life forms and geological events in Earth’s history. Scientists developed the time scale by studying rock layers and fossils world wide. Radioactive dating helped determine the absolute divisions in the time scale.

The Geologic Time Scale Divided into blocks of time called eons, eras and periods.

Broken down Based on events, not number of years

Divisions of Geologic Time Geological time begins with Precambrian Time. Precambrian time covers approximately 88% of Earth’s history.

Paleozoic Era Lasted from 542 to 251 mya.

(AKA the “Age of Reptiles”.) Mesozoic Era Lasted from 251 to 65 mya (AKA the “Age of Reptiles”.)

Cenozoic Era Began 65 mya and is still going on (AKA the Age of Mammals).

Mass Extinction Scientists have evidence that a large asteroid crashed near Mexico’s Yucatan peninsula about 65 mya. The resulting climate change may have caused the extinction of Mesozoic Era reptiles, including most dinosaurs.

Trees and Absolute Dating Trees are like history books. Each tree ring is a record of what the environment was like that year. Wide tree rings indicated a very wet year and narrow rings indicated a dry year.

FYI – oldest plants The oldest tree on record is a bristlecone pine called “Methuselah.” It is 4,765 years old. Gallery Ted Talk – oldest living organisms

Overview of Dating Relative dating is a method of sequencing events in the order they happened they do not tell us when an event happened

Which event happened first?

Absolute dating a method of measuring the age of an object such as a rock or fossil in years tree ring data is very accurate a tree grows one tree ring for every year that it is alive unfortunately, only can go back 5,000 at the most

radiometric dating measures changes in atoms resulting from radioactivity compares the # of radioactive isotopes that are in the object now, to what it had before provides us with a reliable clock that is unaffected by normal forces in nature

carbon dating upper limit is about 50,000 years How Carbon-14 Dating Works (1:07) Carbon dating (2:10)

uranium dating upper limit is billions of years old

The Changing Earth most of the land on Earth was part of a large landmass called Pangea about 250 millions of years ago

during a period of about 250 million years, Pangaea broke apart (continental drift)

Plate Tectonics Tectonic plates large pieces of the crust and part of the mantle called the lithosphere seven very large ones and lots of small ones constantly moving/floating (1-16cm/year) on the plastic part of the mantle because of convection currents in the soft rock underneath them this is called continental drift

Earth 100 Million Years From Now (3:19) http://www.youtube.com/watch?v=uGcDed4xVD4&feature=fvwrel 650 Million Years in under 2 minutes (1:20) http://www.youtube.com/watch?v=NYbTNFN3NBo&feature=related Earth's history in the last 600 million years (1:37) http://www.youtube.com/watch?v=cQVoSyVu9rk&feature=related

For most recent EQ -- http://www.pnsn.org/recenteqs/latest.htm

Warming/Cooling Trends scientists analyze tiny air bubbles trapped in ice cores to learn about past: atmospheric CO2 concentration has increased over 25% over the last few centuries this increase correlates with increase of Earth’s temperatue Siple Station, Antarctica 75°55' S, 83°55' W