Earth History Precambrian Time

Geologic Time  Geologic time can be measured two ways: –Relative Time: –Relative Time: Subdivisions of the Earth's history in a specific order based upon relative age relationships –Absolute Time: –Absolute Time: Numerical ages in "millions of years" or some other measurement

The Geologic Time Scale  The geologic time scale is based on relative time, and is ALWAYS written with the oldest part at the bottom.  Use your ESRT (pg 8-9) to follow along with this presentation.  We will talk about/see a quick review of all of the life on the Earth during its earliest history (the Precambrian).

Divisions of Precambrian Time  The Precambrian is the longest division of Earth’s history (87% of all time).  There are three major subdivisions of Precambrian time. –Hadean –Archaean –Proterozoic VendianVendian

Hadean Time ( Billion Years Ago)  This is the time when the solar system was forming from a nebula. –The age of the formation of the solar system (and earth) come from the ages of the oldest meteorites.  The earth formed, and was probably a hot ball of molten rock.  There are no rocks (and therefore, no fossils) from Haden Time.

Hadean Time Nebula Asteroid/ Meteorite

Archaean Time ( billion years ago)  The Earth cooled enough so that rocks could form.  Earth’s atmosphere was MUCH different than it is now. –Little to no O 2 –More CO 2

The Oldest Fossils  The oldest fossils are approximately 3.7 billion years old. –The first fossils: Bacteria –The only fossil found for the first billion years of biological history on the Earth are bacteria.  The first bacteria were probably responsible for creating oxygen in the atmosphere through photosynthesis.

Bacteria Single-celled organisms Single-celled organisms They currently live in almost every environment on Earth’s surface today. They currently live in almost every environment on Earth’s surface today. Ancient Bacteria Modern Bacteria

Stromatolites  Mounds of algae and bacteria with layers of sediment.  Still found in some few areas today’s oceans –Shark Bay, Australia.

Proterozoic Time (2.5 billion to 544 million years ago)  Most fossils from the Proterozoic are single-celled organisms. –Prokaryote (no nucleus) and Eucaryote (with a nucleus) cells. –Stromatolites are still very common.  In the late Proterozoic (Vendian) some “soft” organisms began to appear.  Most of these organisms died out at the end of the Proterozoic.

Proterozoic Fossils (Vendian Time) Charnia Cyclomedusa

Dickinsonia Spriggina

End of the Precambrian  The end of the Precambrian is marked with the extinction of several of the “strange” animals and the first appearance of hard shells on Cambrian animals.