Earth History

Eons – largest time division Eons determined by major changes in the Earth Most recent Eon started with the appearance of multicellular animals = Phanerozoic Eon Three Eons make up what was previously know as the Precambrian Period 1) Proterozoic 2) Archean 3) Hadean

1. The Hadean Eon: 4.6 to 3.8 billion years ago Earth & other planets formed from dust and gasses surrounding the sun

Gravity gathers dust into large lumps, called planetisimals Collisions between lumps makes lots of heat The Earth was molten during the Hadeon Eon. Steam atmosphere formed from light elements

Heavy elements in the planets suggest the dust/gas came from a supernova We can observe other solar systems forming today They form in diffuse nebulae like nebula M16.

After most planetisimals had become part of a planet, there were fewer collisions Earth’s temperature dropped below 1,000 ۫C First rocks formed as crust cooled The oldest Earth rocks currently known are 3.8 billion years old. The oldest meteorites and lunar rocks are about 4.5 billion years old Erosion and plate tectonics have probably destroyed all of the Earth rocks older than 3.8 billion years.

The Archaean Eon: 3.8 - 2.5 billion years ago Began with the formation of solid rock Volcanic activity added heavier gasses to atmosphere (CO2, N2) Water condensed Early oceans formed First life appeared on Earth

Gasses given off by volcanoes Water Vapor --> 50--60% Carbon Dioxide --> 24% Sulfur --> 13% Nitrogen --> 5.7% Argon --> 0.3% Chlorine --> 0.1% What is missing?

Eon Review: 1) Precambrian – 3 parts a) Hadean b) Archean c) Proterozioc 2) Phanerozic – 3 parts a) paleozoic b) mesozic c) cenozoic

First Life….. 1) Proterozoic Eon = first animals **Before animals there were many types of unicellular organisms single celled living things 2) Phanerozoic Eon = (starts with Paleozoic Era and cambrian explosion) many animals appear

1st living thing =Bacteria 3.4 byo, South Africa 1) Prokaryotic= before nucleus 2) Heterotrophic: eat food(not photosynthetic) 3) anaerobic: no O2 4) fermenters: use organic molecules for chemical energy waste = alcohol + CO2 modern

2nd living things Archaebacteria extremohiles very similar to earliest life forms live in “extreme” environments 1) Anaerobic environments 2) Extreme high temperature (thermophilic) 3) Extreme high salt (halophilic)

Hot Springs Conditions very like Archean Earth High Temperatures Low free oxygen Archeabacteria live here today

Deep Ocean boiling water from vents through crust very stable environment very protected lots of minerals warm -> hot Archaebacteria

The First Energy Crunch organic molecules run low Natural selection for…. organisms that make their own food crisis solved by origin of _____________ Photosynthesis

Cyanobacteria Photosynthetic bacteria – give off O2 Early cyanobacteria were anaerobic so, O2 was toxic to them When their O2 waste product built up.. they died

What Likely Happened O2 made by cyanobacteria at ocean surface O2 toxic to them but not if the O2 was removed by bonding with iron (Fe) Oceans contained dissolved iron

Banded Iron Formations Created iron dissolves in anaerobic water when iron bonds to O2 it becomes solid the solid sinks to the ocean floor is deposited in layers Layers of oxidized iron are red

Dark, Unoxidized Bands Form When all dissolved Fe is removed, O2 builds up High O2 concentrations kill the cyanobacteria Dark sediments are deposited that have no oxidized iron in them

Why are BIFs Banded? When runoff added more Fe to the water the entire process stared over again.

Banded Iron Formations Indirect (non-fossil) evidence for the presence of cyanobacteria ~ 3.5 bya

BIFs (Banded Iron Formations) thick (100s of feet) deposits Precambrian, Australia

BIFs began forming about 3.5 bya = 1st free O2 reached peak about 2.5 bya deposition ended about 1.8 bya

Oxygen Crisis eventually, oxygen built up in oceans then outgassed into the atmosphere oxygen atmosphere led to first major mass extinction anaerobic bacteria restricted to refuges (stagnant water, deep soils, etc.)

Aerobic Bacteria some bacteria evolved antioxidant mechanisms allowed those bacteria to tolerate rising O2 levels some bacteria even evolved to use O2 (aerobic respiration)

How Far Back Does the Fossil Record Extend?

Bacterial fossils preserved in the act of division. 2.1 Billion years old, Hudson Bay, Canada ~3.4 billion years old, South Africa modern bacteria in similar stages of division

Almost Certainly 900 myo - Australia Bitter Springs Formation

Likely 3.1 - 3.2 byo - South Africa Fig Tree Group

3.5 byo - Australia Maybe? Modern cyanobacteria for comparison Warrawoona Group, Australia

Living Precambrian Cyanobacteria Ancient vs. Modern

Why Do We Care Again? build-up of free oxygen started ~ 3.5 bya argues for evolution of photosynthetic life by that time living organisms altered the face of the planet

Earliest (Undisputed) Evidence of Life - Stromatolites 2.2 byo Michigan

Stromatolites dome-shaped, layered structures some 3.5 byo made of layers of bacteria produce abundant oxygen how do we know?

They are still alive today in special environments, notably Shark Bay, Australia Tide In Tide Out

Formation of Stromatolites Cyanobacteria form a mat on top of sediment A new layer of sediment is deposited on top 1 cm Bacteria grow up through new layer

Stromatolites provide evidence for the occurrence of cyanobacteria in the fossil record. Modern Ancient

if we use stromatolites to infer the presence of cyanobacteria we might expect to find fossils of bacteria-like organisms in them...

Gunflint Chert (~2.0 billion years old), Canada And we often find them . . . Gunflint Chert (~2.0 billion years old), Canada

Domains of Living Things (All living things divided into 3 Domains) Oldest domain = Domain Bacteria 2nd Oldest domain = Domain Archaea Most modern domain= Domain Eukarya

Order of Appearance of Life Forms First = heterotrophic/anaerobic bacteria Second = heterotrophic/anaerobic Archaebacteria Third = photosynthetic cyanobacteria Fourth = Aerobic bacteria

Cyanobacteria and the build up of oxygen in the Earth’s atmosphere had 4 significant effects: 1. start of producer based food chain 2. first mass extinction 3. allowed aerobic respiration which let organisms make enough energy to be multicellular 4. Oxygen in air turned into Ozone (O3) Ozone protection from U-V let organisms move onto land