Earth's Climate History

Origins of Earth

• The earth is approximately 4.6 billion years old.
• The Hadean Earth experienced heavy asteroid activity.
• The moon formed, temperature varied, and conditions were extreme.
• The Archean Eon occurred 4-2.5 billion years ago.
• Asteroid activity declined, continents appeared, and life began.
• The atmosphere formed.
• The Proterozoic Eon saw the appearance of supercontinents, changes in the atmosphere, and the rise of eukaryotes.
• Most of Earth's History occurred during the Precambrian period.
• Hadean makes up 13%, Archean 33%, Proterozoic 42%, and Phanerozoic 12% of Earth's History.

Major Changes on Early Earth

• The Earth has undergone major changes to its temperature, atmosphere, and continents, which influenced the emergence of life.
• The atmosphere of early Earth differed significantly from the current atmosphere.
• Early earth saw high fluctuations in CO2 p.p.m.
• Silicate rock turns into soil through weathering.
• Weathering happens more quickly when conditions are hot and wet.
• Carbonic acid interacts with rocks and releases bicarbonate ions.
• Bicarbonate moved into water ways to form calcium carbonate
• Carbon was sequestered in the ocean, lowering CO2, resulting in cooling.
• Photosynthetic organisms emerged 3.5-4 billion years ago.
• Plants emerged about 700 million years ago, removing CO2 from the atmosphere, resulting in an abrupt glaciation.
• Plants contributed to glacial events, also known as snowball earth.
• Snowball Earth happened around 2.2 BYA.
• The second and third periods were less than 1 BYA
• Thawing the earth was due to volcanic activity that increased CO2 in the atmosphere

Atmospheric Composition

• The geological changes explain many atmospheric changes.
• Extreme heat and rain accelerated weathering, leading to carbon sequestration in the ocean and a decline in atmospheric carbon dioxide.
• Rising plants and weather patterns are suggested as causes of Earth's glacial events.
• Greenhouse gases from the Cretaceous period increased global temperatures and sea level.
• Ice ages caused large ice sheets to form and allowed evolution > gene flow.

Continental Shifts

• Earth's crust consists of rigid rock slabs, called plates.
• Plate move, changing continents and oceans.
• Supercontinents include Columbia, Rodinia, Gondwana, and Pangea.
• Columbia was approximately 1800 Ma.
• Rodinia was approximately 1100 Ma.
• Gondwana was approximately 500 Ma.
• Pangea was approximately 250 Ma.

Emergence of Life

• Life appeared in the Archean Eon, two billion years after the Earth formed.
• Life forms became more complex during the Proterozoic Eon.
• Life in the Proterozoic Eon consisted mostly of prokaryotes, also during this time Rodinia supercontinent formed.
• The Cambrian explosion, at approximately 500 MYA, resulted in the extreme diversification of multicellular organisms.

Early Organic Molecules

• Organic, carbon-based molecules must be present for life to exist.
• One theory says meteorites carried organic matter, like glycine, to Earth.
• Theory 2 suggests organic molecules originated on earth.

Early Atmosphere

• The early atmosphere was composed of carbon dioxide, nitrogen gas, water vapor, hydrogen gas, and sulfur, nitrogen, and carbon compounds, and was weakly reducing.
• The early atmosphere lacked free oxygen.

Origin of Organic Molecules

• The Miller-Urey experiment replicated a reducing early Earth atmosphere in hopes of obtaining organic molecules.
• The mixture was rich in hydrogen with no oxygen gas.
• The atmospheric components were placed over liquid water, set to a temperature below 100°C, then stimulated with lightning.
• Methane gas was converted into simple carbon compounds within one week.
• Later experiments produced 30+ carbon compounds, including amino acids.
• Experiments revealed that organic molecules could have formed spontaneously from inorganic sources.

Early Metabolism

• Primitive organisms may have been autotrophic or heterotrophic and were single-celled prokaryotes.
• Eukaryotes eventually evolved.
• Landmarks in the evolution of metabolism include nitrogen fixation, oxygenic photosynthesis, carbon fixation, and nitrogen fixation.
• Biological nitrogen fixation first appeared in archaea approximately 2 BYA.
• Oxygenic photosynthesis resulted in large pulses of oxygen into the atmosphere of late Archean Earth, leading to the Cambrian explosion.

Early Genetic Material and Fossils

• RNA is thought to have been the first genetic material, however, DNA became the primary genetic information thanks to its stability.
• Rock formations 3.5-3.8 billion years old contain microfossils that represent early bacteria and archaea.
• Stromatolites, ancient biofilms that became trapped in minerals, appeared 2.7 BYA.
• Ancient hydrocarbons derived from lipids have been found in rocks.

Diversification on Earth

• Life is categorized into three monophyletic domains: Eubacteria, Archaea, and Eukaryotes.
• Eukaryotes began to diverge around 1.5 BYA and evolved membrane-bound organelles.
• Through the endomembrane system, eukaryotic cells were better able to regulate gene expression.
• Eukaryotic organelles, like mitochondria and chloroplasts, generated energy.
• Mitochondria and chloroplasts are thought to have evolved through endosymbiosis, where organisms engulfed other organisms.
• Multicellularity allowed organisms to differentiate into different cell specializations for survival and proliferation.
• The Cambrian Period saw rapid diversification because of these innovations.

Earth's Systems + Evolution

• Continental shifts affected gene flow and evolution.
• Reproductively isolating populations and allowing previously separate populations to interbreed
• Continental collisions created large mountain ranges isolating previously interbreeding populations during the Carboniferous and Permian periods.
• The separation of Greenland and North America, along with Australia and Antarctica, caused reproductive isolation about 66 million years ago.
• Evolution of photosynthesis protected organisms on land due to increased ozone.
• The first animals were likely invertebrates.
• Adapted to prevent desiccation and gain water.

Explore Earth's climate history. This includes silicate weathering, volcanic activity, and the impact of plant emergence on CO2 levels and glaciation. Also covers key events in Earth's history, the colonization of land by plants, and animal adaptations.