The Precambrian Time Last from 5 billion years ago – 544 million years ago
Key Events of Precambrian time Acasta Gneiss is dated at 3.96 bya. It is near Yellowknife Lake , NWT Canada Zircons possibly a bit older in Australia
Precambrian • 4.6 billion years to 544 million years. • Represents 88% of Earth’s history • 3 divisions • Hadean • Archaen • Proterozoic
EarlyHadean (hellish) Time • 4.6 billion years ago – Earth forms from “stardust” • Earth is bombarded by impactors adding to Earth’s mass (adds heat) • Hot spinning planetary mass caused materials to layer according to density (crust, mantle, core). • Heavy iron and nickel migrate to center (core) • Medium density silicate material moves out to mantle • Lightest float to the crust
Hadean Formation of Continents • Early earth surface was magma sea, gradually cooled to form the crust.
EarlyArchaean • Huge glancing blow from a Mars-sized impactor created the moon. (Collision Theory)
PrecambrianEarly Atmosphere • 1st atmosphere was H + He • lost to solar wind • Later mostly Nitrogen (inert) and CO2 • Liquid water rids CO2 from atmosphere • Mars is too cold to have liquid water. • Venus is too hot. • Both have CO2 atmospheres. • On Earth, most of the world’s CO2 is locked up in rock and life! Mars Venus Earth
PrecambrianEarly Oceans about 4 billion years ago • volcanic stem condenses • Part of the earth’s water probably came from comets • comets are large dirty snowballs • provide fresh water • salt in oceans from weathering and carried to the oceans by rivers
. 3.5 bya - Origin of LifeOrigin of Archaebacteria • Archaebacteria are the most primitive fossil life forms • likely ancestors of all life • thermophiles • in deep-sea volcanic vents • feed directly on sulfur (chemosynthesis)
Why at the vents? • chemical and heat energy • abundant chemical and mineral compounds, including sulfur • protection from oxygen and ultraviolet radiation
Move to Photosynthesis By 2 billion yrs ago CYANOBACTERIA Moved from vents to water surface Began using sunlight to make food
2 bya Photosynthesis Modern StromatolitesShark Bay Australia Used to dominate the landscape in Pre-Cambrian and Early Cambrian.
2bya - Proterozoic Time:Oxygen - Rich Atmosphere • Oxygen in atmosphere irradiated - Ozone layer forms, protecting shallow water and land life forms from UV
1.9 bya - Rodinia N Metamorphic alteration of magnetic minerals makes arrangement uncertain. Most of North America “Boxed-In” Note orientation and neighbors of “North America”
Snowball Earth 600 million years ago • Atmosphere’sCO2 tied up in extensive limestones. • No greenhouse effect. • Atmosphere can’t trap heat – gets colder • Oceans froze
570-545 million year ago-late Proterozoic Time • Multi-cellular organisms appear (algae strands, jellyfish, etc.) • Ediacaran (Vendian) consist of simple flat, platelike organisms.
Proterozoic Life Ediacara Fauna
Check yourself You may choose more than one letter for some questions! Select ALL that apply for each question.
1. During which Precambrian division do the oceans form? • Phanerozoic • Hadean • Archaean • Proterozoic
2. What formed the oceans? • Water from the core • Comets • Volcanic vapors • Asteroids
3. During which Precambrian division is Snowball Earth? • Phanerozoic • Hadean • Archaean • Proterozoic
4. Put the following events in order as they occurred during the Precambrian Eon • jellyfish & ediacarans • hydrogen & helium atmosphere • Single-celled thermophile bacteria • cyanobacteria • Oceans form • Oxygen-rich atmosphere
5. What is a major difference between Precambrian archaebacteria & cyanobacteria? • Cyano came first • Archae used photosynthesis, while cyano used chemicals like sulfur • Cyano lived closer to the ocean’s surface than the archae did D. Cyano lived along volcanic vents in the ocean floor and archae lived on land
6 – 10. Explain IN DETAIL how the Precambrian Earth was different than modern day Earth with respect to temperature, biota (life), atmosphere, age.