HISTORY OF LIFE

Chapter 14

The Record of Life

Ch. 14, Sec 1

Early History of Earth

• 5 billion years ago our solar system was formed as a swirling mass of gas and dust

• Gravity pulled this material together to form the sun

• Remaining gas and debris circled the newly formed sun

• Collisions between the space debris created the planets

• Earth formed about 4.6 billion years ago, dated by studying the layers of rock that make up the planet

• Young Earth was hot, there was no atmosphere to block UV rays from the sun

• No oxygen to breath• A lot of carbon dioxide and

water

• Life originated in Earth’s oceans 3.9-3.4 billion years ago

• Early life forms would have been very similar to bacteria

History in Rocks• Rocks provide information about Earth’s history

including the history of life on Earth• Paleontologists study ancient life and fossils

• Fossils are found in sedimentary rock• Organism gets buried in mud, sand, or clay

after they die• More sediment gets layered over the

organism, over time the minerals in the sediment replace the minerals in the skeleton

Dating Fossils

• Relative Dating = layers of rocks have different ages, the “youngest” layers on top; older fossils found in older layers of rock

• Radiometric Dating = atoms in the fossil break down at a certain rate, age of the fossil depends on the ratio of atoms to broken down atoms

Geologic Timescale

• Begins with the formation of Earth and goes through present time

• Scale is divided up by the kinds of organisms that lived during that time

• Layers of rock match up with the Geological Timescale

Organization of the GTS

• Broken down into 4 Eras, each era is further broken down into Periods

• The eras and periods are characterized by specific events and specific organisms

• Mass Extinction = many organisms disappear from the GTS almost all at once

4 Eras

1. Precambrian Era• Beginning of the GTS, longest era 87% of

Earth’s history• Oldest rocks are from the Precambrian, oldest

fossils too• First organisms were single celled

2. Paleozoic Era• Cambrian Explosion

occurred during the Cambrian Period

• Enormous increased in diversity of life in oceans

• Organisms with backbones emerged

• Mass extinction occurred at the end of the Paleozoic Era killing off 90% marine life, 70% land life

3. Mesozoic Era• began 248 million years

ago• Dinosaurs died out

during another mass extinction making room for mammals

• Meteor crash could have caused the mass extinction

4. Cenozoic Era• Began 65 million years

ago• Increased diversity in

mammalian life• Modern humans

appeared 200,000 years ago

• As you move towards the bottom of the rock layers, you move back on the Geological Timescale

• Similar fossils found on different continents because at several times in Earth’s history the continents were connected

• Pangea existed 250 million years ago

• Plate Tectonics = the surface of Earth is made up of plates that drift on top of a molten layer of rock

• http://www.nature.nps.gov/geology/usgsnps/animate/PLATES_3.MPG

• http://www.ucmp.berkeley.edu/geology/tecall1_4.mov