Chapter 12

How old is the earth? 4.3 billion years! Just how big is a billion? If you laid 1 billion $1 bills end to end, they would encircle the earth four times If you stacked the bills on top of each other, the pile would be more than 47 miles high If you wanted to count 1 billion $1 ills, it would take about 5787 days (almost 16 years) If you saved $100 per day, it would take you 27, years to save 1 billion dollars

How do we know how old the earth is Radiometric dating Unstable isotopes (atoms with varying numbers of neutrons) decay at known rates and can be used to calculate the age of materials Half-life is the amount of time it takes for half of the isotopes to decay into a different element Uranium isotopes have a half-life of 4.5 billion years Carbon isotopes (used to estimate organic remains) have a half-life of 5730 years Relative dating Time estimations based on layers of rock

Geologic time scale Since the earth is so old, we organize it into time periods Eras (tens to hundreds of millions of years) Periods (tens of millions of years) Epochs (several million years) Currently living in the Cenozoic era, which began 65 million years ago. Living in the quaternary period, which began 1.8mya Animal life took off during the Cambrian Explosion about 544 million years ago

How do we compare to the age of the earth? Anatomically modern humans have only been on earth for 100,000 years This is a blink of an eye on a geologic time scale Video The Evolution of Life in 60 seconds

Cyanobacteria and Endosymbiosis Earliest fossils were cyanobacteria Photosynthetic Changed composition of atmosphere Endosymbiotic theory Explains how first eukaryotes came to be Larger prokaryote engulfed smaller prokaryotic and began symbiotic (mutually beneficial) relationship