chapter 12

age of human transformation of Earth’s biological and physical systems

4.6 billion

gases emmitted by volcanos

photosynthetic bacteria that helped put oxygen into our atmopshere

colonies of cyanobacteria. fossils date back to 3.5 bill years

4.6 bill

the principle that the same gradual and nearly imperceptible processes operating now have operated in the past

relative age: compares age of one object or event with age of another without specifying how old either is — accounts for order of events Absolute age: an age that is specified in years before the present

In a sequence of rock layers, the oldest rocks are at the bottom, and the youngest rocks are at the top

dendrochronology (tree ring analysis) Radiometric dating

CoreMantleLithosphere

composed of solid iron and nickelExtends from Earth’s center to about 5,150 km (3,200 mi) below Earth’s surfac

composed of liquid iron and nickelExtends to about 2,900 km (1,800 mi) below Earth’s surface

continental and oceanic

Magma: melted rock that is below the surface of the crust. Often hardens into granite Lava: magma that spills onto the surface of Earth’s crustOften hardens into basalt