The History of Earth

The Big Bang• By measuring the rate at which all

galaxies are moving away from each other, it can be calculated that everything in the universe existed in an infinitely small single point called a singularity about 13.7 bya

• Using a branch of physics called quantum mechanics, it can be shown how a singularity such as the one that caused the Big Bang can spontaneously come into existence

• Within milliseconds, this singularity suddenly split into energy and dark energy that exploded away in all directions

• Much of the normal energy was converted into matter as it moved away from the singularity (E=mc2)

• The dark energy from the Big Bang permeates throughout the universe and continues to propel galaxies away from each other to this day

Formation of Galaxies• Around 1 billion years after

the big bang, gravitational pull caused matter floating throughout the cosmos to begin clumping together

• As these clumps of matter began to get extremely dense, high pressures caused hydrogen fusion reactions to initialize in their cores, giving birth to stars

• These stars began orbiting around super-massive black holes giving rise to galaxies

The Milky Way• Around 200 Billion

galaxies are estimated to exist

• Our galaxy is known as the Milky Way

• 200-400 billion stars, 50 billion planets, 500 million within habitable zone of mother star (all estimates)

• Closest galaxy is the Andromeda Galaxy 2.5 million light years away

The Solar System• Sometimes a massive star can

go supernova ejecting a huge amount of matter into space creating a nebula

• Nebula matter consists of the 92 naturally occurring elements in different ratios that were created under high pressures within the supernova

• Over time, one such nebula began to collapse under its own gravitational pull and created our solar system around 4.6 billion years ago

Formation of the Earth & Moon• Within the accretion disk that

was left around our sun, Earth Mark 1 formed within the habitable zone

• 30-50 million years afterwards, a 5th inner planet, known as Theia, collided with Earth Mark 1 ejecting molten rock into orbit

• This rock formed temporary rings around what was now Earth Mark 2

• Within another 100 years or so, the rings coalesced into the moon

Importance of the Moon• The moon is extremely important

because its gravitational influence stabilizes our rotation on a 23.5° axial tilt

• Without the moon, our axial tilt would fluctuate between 0° and 90° wreaking havoc on our climate

• The earth wobbles 360° around this tilt once every 26,000 years

• Within every 30° of this 360° rotation, the earth lines up with a Zodiac constellation

• This occurs once every 2160 years on the winter solstice

• This “Precession of the Ages” will begin again on 12/21/2012 marking the end of the Age of Pieces and the beginning of the Age of Aquarius

Timeline of the Earth• The history of the earth is

divided into 4 Eons that cover the entire 4.6 billion year existence of the planet

• The first 3 Eons are known collectively as the Precambrian and cover 90% of earth’s history

• The last Eon is divided into 3 Eras that are further divided into Periods

• The two Periods in the most recent Era are further divided into Epochs

The Hadean Eon• 4.6-3.8 bya• Time before there was a

solid surface on the earth• The moon formation event

and the late-heavy bombardment occurred during this time

• The inner planets were bombarded by comets and asteroids that presumably brought most of the earth’s water as well as amino acids necessary for life to form

The Archean Eon• 3.8-2.5 bya• Began with the formation of

the first solid rock and ended with the continents fully formed (though not in the present shape or distribution)

• Earth was still very hot due to core heat, volcanism, and radioactive decay

• Prokaryotic life began in the time around the boundary between the Hadean and Archean Eons

The Archean Eon• Late in the Eon,

photosynthesis evolved and stromatolites, the most ancient organisms still living on the planet, began pumping O2 into the atmosphere

• Most of the O2 was pulled down into the oceans that were greenish brown due to high amounts of dissolved iron in the water

• The iron fully oxidized (rusted out) and the oceans turned blue by the end of the Archean Eon

The Proterozoic Eon• 2.5 bya - 542 mya• Marked by the major

accumulation of O2 in atmosphere

• Led to first eukaryotic life around 2 bya

• Proliferation of photosynthetic organisms began to take too much CO2 out of the atmosphere cooling the poles and creating extra ice cover

• An ice-albedo feedback caused global cooling on an unprecedented scale

Snowball Earth• At the end of the Proterozoic

Eon the earth froze solid, as evidenced by glacial rock deposits in areas that were equatorial at the time

• Once the earth was frozen, CO2 was no longer able to be utilized for photosynthesis and began to increase due to volcanism

• Eventually, rising CO2 began to trap heat and the snowball earth melted marking the end of the Eon and the entire Precambrian as a whole

Snowball Earth

Multicellular Life• At the end of snowball earth,

melting glaciers washed massive amounts of pulverized rock and minerals into the oceans providing fuel for another round of heavy photosynthetic activity

• Rising O2 levels allowed single-celled organisms to start using excess O2 to begin building collagen and “gluing” themselves together

• This was the beginning of multicellular life and can be seen in action if a sponge is passed through a sieve

Multicellular Life• Multicellular organisms had

many advantages over their single-celled cousins

• Cells could now work together to find food or defend against predation, or they could begin to differentiate and take over specific tasks

• There were two major developments of multicellular life on earth – the first was not very successful and lasted only 30-50 million years. The second led to all the present multicellular life forms on earth today

Fractal Organisms• The first multicellular life

forms evolved as snowball earth was melting and grew by fractal, or modular construction

• Their bodies were flat and were anchored to the sea floor in complete darkness

• With no mouth or sensory structures, these organisms simply absorbed nutrients through their thin, flat bodies

Fractal Organisms• The most common fossil of fractal

organisms is called Charnia• It appears all over the world in

rock that is around 560 million years old and was deep underwater at the time of its formation

• Due to fractal construction, it and others like it were unable to evolve into more complex life forms and were out-completed by organisms that were to be our ancestors

• The fractal organism life line ceased at the end of the Proterozoic Eon

The Phanerozoic Eon

• 542 mya – Present• Divided into 3 Eras – The

Paleozoic, Mesozoic, and Cenozoic Eras

• The ends of the Paleozoic and Mesozoic Eras were marked by mass extinctions

• The Cenozoic Era is still continuing today

The Paleozoic Era• 542 – 251 mya• Began with the Cambrian

Period and ended with the Permian Period

• The Paleozoic Era was marked by the evolution of most modern animal phyla, the formation and break-up of several supercontinents, and the colonization of land by plants and animals

The Cambrian Explosion• With the uptick in

atmospheric O2 at the end of snowball earth, multicellular life began to evolve extremely rapidly

• Within a few million years, organisms began to develop mobility and the first modern animals were born

• Future generations began to evolve features like teeth and claws that allowed them to become more successful hunters and their prey followed suit by developing defensive structures like shells

The Cambrian Explosion• This “arms race” fueled

evolution’s progress and within 20 million years of the beginning of the age, all present animal phyla had evolved

• This event that marked the 20 million year span of rapid evolutionary development is known as the Cambrian Explosion

• The best place in the world to see evidence of this is the Burgess Shale in the Canadian Rockies of British Colombia

Periods of the Paleozoic• Cambrian – explosion of life• Ordovician – adaptive

radiation of animal phyla formed during the Cambrian including the formation of vertebrates

• Silurian – major arthropod advancements and beginning of land plants

• Devonian – invertebrates and amphibians colonized land

• Carboniferous – large swamp forests that led to all coal formations today and the development of land reptiles

• Permian – proto-mammals evolved out of reptiles

The P-T Extinction Event• At the end of the Permian Period,

the climate of the earth began changing

• The formation of Pangaea created a super-desert over much of the land on earth and caused oceanic currents to change altering the weather and rain cycles severely

• Then, 251 mya, a super-volcano in present-day Siberia erupted causing a “nuclear winter” that lasted years

• Many species already in trouble due to environmental pressures caused by Pangaea could not survive the conditions over the next few years and 83% of all genera on the planet were wiped out

The Mesozoic Era• 250-65 mya• Marked on both sides by

the two largest extinction events in history

• The “Age of the Dinosaurs”

• The P-T Extinction at the end of the Permian allowed for massive adaptive radiation of remaining species

• Broken into 3 Periods – The Triassic, Jurassic, and Cretaceous

The Triassic Period• 250-200 mya• Began at the end of the

Permian-Triassic Extinction event

• Pangaea remained intact throughout the Triassic

• The first dinosaurs evolved during the mid-Triassic including Pterosaurs and the small Coelophysis and their relatives

• Advanced Cynodonts gave rise to the first mammals midway through the Triassic as well

The Jurassic Period• 200-145 mya• Beginning of Jurassic is marked

by the initial breakup of Pangaea into the two supercontinents Laurasia and Gondwanaland

• Large herbivorous dinosaurs like the brontosaurus, marine dinosaurs like the ichthyosaurs, and pterosaurs were the dominant dinosaurs at this time

• Mammals were small and insignificant

• End of Jurassic was marked by the appearance of flowering plants on earth

Triassic/Jurassic

The Cretaceous Period• 145-65 mya• Dinosaurs evolved into their

peak diversity during the Cretaceous

• T-Rex, Triceratops, Velociraptor, and modern birds all evolved

• Laurasia and Gondwanaland broke up into the today’s continents, but they were not yet in their present positions

• The Cretaceous and the entire Mesozoic Era came to an end with an asteroid impact near the present-day Yucatan Peninsula

The K-T Extinction• Called the Cretaceous-Tertiary

Extinction event• The asteroid impact threw ash

into the atmosphere blocking out most sunlight for years

• Most photosynthetic plants died, leaving no food for the large herbivorous dinosaurs that required massive amounts of energy daily

• All non-avian dinosaurs, pterosaurs, and marine reptiles perished along with many other species

• When the ash settled, the stage was finally set for mammals to take over the earth

The Cenozoic Era• 65 mya – Present• The “Age of Mammals”• Continents moved into

their present positions• The movement of

Antarctica to the south pole and the joining of South America to North America altered oceanic currents and led to global cooling

• Forest swamps of the Mesozoic Era gave way to large areas of grasslands in the Cenozoic Era

The Cenozoic Era

• Mammals diverged from a few small, generalized forms to the plethora of terrestrial, marine, and flying types of the present

• Birds diversified and flowering plant/insect relationships developed as well

• Snakes and modern lizards, the newest reptiles evolved during the Cenozoic

• The Cenozoic Era is divided into 3 Periods

Periods of the Cenozoic• The Paleogene Period

– 65-23 mya– The most significant

evolution of birds and mammals occurred in the Paleogene

– Ended with a minor extinction event affecting mammals

• The Neogene Period– 23-2.5 mya– Creation of the Panama

Isthmus and the resulting global cool-down were the defining events of the period

Periods of the Cenozoic• The most recent Period of

history is the Quaternary (2.5 mya- Present)

• Marked by the rise of Homo sapiens

• Though primates had been evolving since the K-T Extinction 65 mya, the Homo line had been evolving since the Neogene Period 6-7 mya

• During the Quaternary, Homo neanderthalensis, Homo erectus, and Homo sapiens all fought for resources and interbred until the present form of humans were the only species left by 30,000 years ago

Periods of the Cenozoic• The Quaternary is divided into

two important Epochs• The Pleistocene

– 2.5 mya - ~12,000 years ago– The Ice Ages– Marked by 11 known glaciations

that covered 30% of the earth’s surface at each maximum

– Glaciations as well as development and subsequent predation by humans drove most mega-mammals to extinction

• The Holocene– ~12,000 years ago – Present Day– Considered an interglacial period

during the present ice ages– All of humanity has occurred in

this brief warm period of time, roughly 0.0003% of the history of the world

The Future of the Earth

• The Earth will not remain a planet conducive to human life forever

• Many changes are expected to occur over the next 7.5 billion years until the Earth is ultimately destroyed by our sun

The Next Ice Age• Greenhouse gasses will rise

until all fossil fuels run out by ~2200 AD

• The next ice age is expected to begin 25,000 years from now, but global warming may only delay the onset for 5,000 years or so

• Human civilization would have to adapt dramatically to survive the glaciation event that would last tens of thousands of years

Future Supercontinents• Plate tectonics will continue

until the earth’s core cools past a point necessary for mantle convection to occur

• Two theories predict the next supercontinent that will be produced in ~250 million years– Introversion Theory predicts

that the Atlantic and Indian oceans would widen until new subduction zones form causing them to collapse forming Pangaea Ultima

– Extroversion Theory predicts that the Atlantic will continue to expand and the Pacific will continue to contract until the Americas collide with Asia and create Amasia or Novopangaea

Future Supercontinents• The formation of a new

supercontinent would alter the entire climate of the earth in unforeseen ways

• Eventually the core of the earth will cool to a point where continental drift will cease

• The dynamo effect of the spinning metallic core of the earth would continue for millions of years after the continents stop moving

• Eventually the core will stop spinning all together causing the magnetic field around the earth to break down

• Solar radiation would then begin bombarding the earth destroying DNA at the cellular level putting all life on earth in jeopardy

Earth Becomes Like Venus, Then Mars

• As the sun ages and solar output increases the temperature on the earth will eventually rise

• Once the sun is 10% more powerful than today (1.1 billion years from now) it will begin evaporating the oceans into the atmosphere

• The atmosphere will become saturated with water, a greenhouse gas, and a runaway greenhouse planet like Venus will form

• Once the magnetic field breaks down, the solar winds will blow the water/atmosphere out into space leaving a dead, dry planet like Mars

Future of the Moon• The moon is very large to earth when

compared with other planets/moons• The moon is slowing down the spin of

the earth by way of tidal braking• At the same time, the tidal braking is

also speeding up the orbit of the moon causing the moon to move away from the earth 1 inch further each year

• Eventually, tidal breaking will cease when the moon’s orbit and the earth’s day both equal 47 modern days in length, about 3 billion years from now

• Once the moon is this far away, it will lose its ability to stabilize the earth on its axis

• The earth would begin to tumble in its orbit and the climate would never be stable again

Red Giant• The hydrogen core of the sun

will begin to run out of fuel in the next 6-7 billion years or so

• As this happens, the sun will begin to consume the hydrogen in its outer regions

• This will cause the outer regions of the sun to expand rapidly until the edge of the sun reaches about as far as earth’s present orbit

• The earth may not actually be swallowed up by the sun, but its luminosity is expected to increase to 2,730 times its present power essentially cooking the earth

Fate of the Solar System• The sun does not have enough

mass to become a supernova and explode to seed a new solar system

• Instead, once the sun enters the red giant phase, it will begin to throw its mass out into space until its white-hot core is all that is left

• This white dwarf will enter its final phase of life once it has cooled to the point that no more light is emitted

• At this point, it will be a black dwarf or a mini black hole

Fate of the Universe• The Big Freeze

– Theory that proposes that our universe is open and will continue to expand and lose heat until it is completely dark and everything in the universe is at absolute zero

• The Big Crunch– Theory that proposes that the

mass of the universe will eventually overpower its expansion and it will contract back to a singularity similar to the one that brought about the Big Bang

– This theory predicts a closed, oscillatory universe that cycles in and out of existence