History of Earth

• The sun and planets were formed from a rotating gas cloud that collapsed gravitationally.
• By 4,600 Ma, Earth formed and was initially molten.
• Earth's history is separated into named time periods making referencing easier.

Time Scale

• Eon is the largest division of geologic time, followed by Era, Period, and Epoch.
• The Hadean Eon represents Earth's earliest history.
• The Archean Eon came after the Hadean Eon.
• The Proterozoic Eon followed the Archean and was succeeded by the Phanerozoic Eon.
• The Phanerozoic Eon is the current eon, characterized by abundant visible life.
• Eras within the Phanerozoic Eon include the Paleozoic, Mesozoic, and Cenozoic.

Earth's First Atmospheres

• The first atmosphere (Atmosphere #1) contained gases like H2 and He that escaped into space.
• Gases such as H2O, CO2, and NH3 were present in the 2nd atmosphere (Atmosphere #2).
• The current, third, atmosphere (Atmosphere #3) contains H2O, CO2, O3, O2, and N2.

Seafloor Hydrothermal Vents Theory

• Deep-sea life thrives near hydrothermal vents, such as those near the Galápagos Islands.
• These "black smokers" may have provided suitable environments for the origin of life.

Photosynthesis

• Plants use photosynthesis to create carbohydrates.
• The process combines carbon dioxide and water.
• Molecules containing carbon, hydrogen, and oxygen.
• The reaction produces oxygen (O2).

Oxygenation Event and Stromatolites

• The oxygenation of Earth is considered to have been started by the oxygenic photosynthesis of cyanobacteria.
• Stromatolites form in warm, shallow seas due to photosynthetic bacteria.
• These are sandy mats created by such bacteria
• The oldest stromatolite dates back to 3.4 Ga (Giga-annum, or billions of years).
• The Great Oxidation Event is marked by biomarker evidence of cyanobacteria around 2.8 Ga.
• The atmospheric oxygen increase began approximately 2.45 Ga.
• Early atmosphere oxygen was initially absorbed by the oceans or seabed.
• Oxygen later accumulated in the atmosphere, leading to the formation of the ozone layer.

Replication and Early Life

• Modern replication depends on a complex mechanism.
• DNA (deoxyribonucleic acid) is the double chain biopolymer containing an organism's genetic code.
• It is needed for organisms to grow and reproduce.
• Early life likely used a simpler self-replicating molecule called RNA (ribonucleic acid).

Prokaryotes and Eukaryotes

• The most ancient fossils are remains of microscopic prokaryotes.
• Prokaryotes are single-celled with no distinct nucleus and no separation of DNA.
• Biologists know three domains, which is the broadest taxonomic category.
• These domains are Bacteria, Archaea, and Eukarya
• Eukaryotes are organisms with cells containing a well-defined nucleus and organelles.
• Eukaryotic cells likely evolved from prokaryotic cells, with one engulfing another.
• Eukaryotic cells are in multicellular organisms.

DNA Mutation and Species

• After DNA came into existence, life had emerged.
• Evolution of the earliest life forms was assured because DNA can mutate.
• Evolution of species happens if smaller populations are isolated

Ediacaran Biota

• Multicellular organisms became abundant around 600 Ma, during the Ediacaran period (635-542 Ma).

Fossils

• Fossils offer evidence for evolution.
• Organism remains embedded in rock and preserved from a past age
• Fossils form when protectively covered.
• Fossil formation involves the burial of remains, sediment accumulation, and fossilization over time.
• Trace fossils are fossilized evidence which include tracks, footprints, and burrows.
• Not all fossils are bones, but those are the most common.

Cambrian Explosion

• Organisms with hard parts appeared near the start of the Cambrian period, about 570 Ma.
• This event is known as the Cambrian explosion of life.
• Life existed only in seas at this time.
• Trilobites, extinct arthropods, were a group that dominated.
• The Burgess Shale is found in British Columbia and known for numerous soft-bodied life forms.
• These included Waptia fiedensis, an arthropod 3 cm (1.25 in) in length.
• Brachiopods existed and are still a very small group.

Paleozoic

• Trilobites' importance waned throughout the Paleozoic Era.
• Jawed fishes also appeared in this era.

Land Plants

• Land plants evolved from green algae.
• Vascular plants emerged in the Silurian period (443-416 Ma).
• Plants had structural limbs and stems for support.
• Vessels transferred water and dissolved elements.
• Gas exchange was through diffusion.

Carboniferous

• The Carboniferous Period, from 354 to 64 Ma, was known for vast swamp forests.
• It created extensive deposits of coal, which is a carbon-rich sedimentary rock.
• Plants included Archaeopteris (30m tree), Lycopsids (1.5m & 0.2m), and Asterophyllites.
• Extensive swampy areas were abundant and arthropods evolved to live on land.

Devonian

• The Devonian Period is known as the Age of Fishes.
• Late Devonian lobe-finned fish and amphibious tetrapods existed.

Permian

• Reptiles developed during the Permian pd, from 300-250 Ma.
• These reptiles evolved into mammals and dinosaurs.

Mesozoic

• Reptiles greatly increased in diversity in the Jurassic period.
• Jurassic lasted from ~200 to 148 Ma.
• Dinosaurs of the Jurassic pd. grew to huge sizes and were the largest land mammals.
• During the Cretaceous Period Flowering plants developed.
• Dinosaurs dominated the Earth for 150 million years.

Mass Extinctions

• A mass extinction is rapid and catastrophic wiping out a fraction of all species.
• The most famous mass extinction occurred 65 million years ago.
• About 70% of all species died out.
• The K-T extinction had other evidence that supported it.
• Iridium in surrounding rocks, as it is rare on Earth.
• The Chicxulub crater is in the Gulf of Mexico.

Volcanism and Mass Extinction

• The Siberian Traps spanned Russia and neighboring contries.
• The Deccan Traps region spanned much of india.
• Most major extinction events also contain evidence of large scale volcanic activity.

Cenozoic

• Dinosaurs' dissapearance allowed mammals to evolve and diversify
• By the end of Mesozoic era, 70% of species were wiped out.
• The Quaternary Period featured major glaciations and large land animals known as megafauna.
• 4.4 million years ago hominids appeared.
• Homo erectus was the first species in our genus.
• Stone tools began being used by Homo habilis around 2.4 million years ago.
• Fossil records dont show where we (Homo sapiens) came from