Fossil Evidence of ChangePart 2

Chapter 14Section 1

Dating FossilsRelative dating is a method used to determine the age of rocks by comparing them with those in other layers.

Law of superposition states that younger layers of rock are deposited on top of older layers

Radiometric dating uses the decay of radioactive isotopes to measure the age of a rock

This method requires that the half-life of the isotope, which is the amount of time it takes for half of the original isotope to decay, is known.

Uranium 238 decays to Lead 206 with a half-life of 4510 million years.

Geologic Time Scale (GTS)GTS is a record of Earth’s history

Epochs are the smallest unit of geologic time lasting several million years

Periods are divisions of geologic time lasting tens of millions are years

Era is a unit of geologic time consisting of 2 or more periods that lasts hundreds of millions of years

http://www.geo.ucalgary.ca/~macrae/timescale/time_scale.gif

PrecambrianFirst 4 billion years

Life 1st appeared cyanobacteria and eukaryotic cells also emerged

The Paleozoic EraIn just a few million years, the ancestors of most major animal groups diversified in what scientists call the Cambrian explosion.

1st life on land emerged during this era

Mass extinctions have occurred every 26-30 million years on average

Between 60-75% of the species alive went extinct in each of these events

The cause of these extinctions include geological forces and increased volcanic activity disrupting ecosystems and changing climate

The Mesozoic EraMammals and

dinosaurs fist appeared Flowering plants evolved from non-flower plants

Birds evolved from a group of predatory dinosaurs

65 million years ago, a meteorite struck Earth

Paleontologists have evidence of this due to the large amounts of iridium which is rare on Earth, but common on meteorites

The meteor probably did not wipe out all the species, but debris from the impact probably stayed in the atmosphere for months or even years affecting global climate

The Cenozoic EraIs the most recent era

Mammals became the dominant land animals

Humans appeared near the end in the Neogene period