Are there other stars and planets like ours?  Why is our planet so right for us?  How did Earth get to be the way it is?  How will the world end?

2.3 Astronomical and Geological Conclusions                                                            (Statement 9)

Science currently explains how the solar system, with the earth and moon, developed:

●          How a cloud of dust and gas evolved into the sun, the planets, the Earth and the Moon;

●          Why on Earth we have years, seasons, tides, night and day;

●          How on Earth we came to have seas, land masses, volcanoes, earthquakes, mountains, rivers, the air, the winds, ocean currents, the climate, the weather.

Science predicts that the Earth will uninhabitable after a billion or so years.

… more

2.3.1   Our galaxy, the Milky Way, is a flat disk with spiral arms.  On a moonless night we see this side on, as a band of many stars in a hazy, luminous band stretching across the sky.  It started about 3-5 billion years after the big bang and is about 9 billion years old.  There is a black hole at its centre, then globular clusters.  It has billions of stars and regions of dense interstellar gas, called nebulae, where, with telescopes, we can see stars being formed.  A few new stars have been forming each year in our galaxy for billions of years.  more (later)

2.3.2   Our Sun is a third generation, middle sized star.  It formed about 4.7 billion years ago, out of interstellar gas, dust and ices, taking about 100,000 years.  Because it was rotating it formed into a flat, spinning disk, around the young Sun.  more (later)

2.3.3   As time went on, the grains and ices in the disk bumped into and stuck to one another.  As they grew larger, their gravitational forces increased, attracting more matter from the disk and gradually building up kilometre-sized bodies called planetesimals, and some of these became planets.  Other planetesimals became either comets or asteroids.  They all revolve around the sun in roughly the same plane.  more (later)

2.3.4   High energy particles flying out of the early sun (the solar wind) pushed the lighter gases away from the centre, so the outer planets (Jupiter, Saturn, Uranus and Neptune) are mostly made of gas (the gas giants).  The heavier dust particles were not pushed so far, so the inner planets (Mercury, Venus, Earth and Mars) are rocky (earth-like planets) containing heavier elements.  more (later)

2.3.5   The heavier iron and nickel sank to the middle and lighter rock (lava) floated to the surface.  Fast moving dust particles crashing into the early earth made the surface heat up and melt, and initially warmed the earth’s core.  Uranium, thorium and potassium in the earth’s core break apart and produce heat which is trapped in the core so it heats up.  These are gradually being used up.  more (later) 

2.3.6   Another planetesimal crashed into the early earth then bounced away but gravity keeps it spiralling around the Earth, slowly getting further away.  This is the Moon.  It has similar rocks to the Earth, and they show that the moon is about 4.5 billion years old.  The moon initially had a faster rotation but gravity (tidal forces) slowed this down so that now only one side of the moon faces the earth.  The moon reflects the sun’s light.  It revolves around the earth every 28 days.  Part of that time it is in the earth’s shadow, which causes the phases of the moon.  more (later) 

2.3.7   The earth’s path around the sun is not exactly a circle but is an ellipse.  Its path on average is about 150 million kilometres from the sun.  In the southern winter/northern summer the earth is about 5 million kilometres further away from the sun, and we get about 7% less sunlight than in the southern summer/northern winter.  It slows down as it moves further away and speeds up as it gets closer to the sun.  The northern summer is a few days longer than the southern summer, when it is revolving more slowly.  more (later)

2.3.8   The earth acquired a spin from the original rotating solar cloud or from being hit by the moon.  This means we have day and night.  Days are gradually getting longer.  more (later) 

2.3.9   The spin axis is tilted – inclined – to the plane of the solar system.  This means that when the earth is in one position in its orbit around the sun the sun is more directly overhead in the southern hemisphere, but half a year later the sun is more directly overhead in the northern hemisphere.  This generates the seasons.  more (later) 

2.3.10 The spin axis of the earth wobbles a bit, and goes through a cycle of about 25,800 years.  This causes the positions of the starts to change relative to us.  more (later)

2.3.11 As the earth cooled the molten lava at the surface hardened to become basalt, granite and pumice rock.  The centre of the earth remains molten iron, though it is gradually cooling down.  The gas giants, by comparison, don’t have hard surfaces.  The gas they are made of becomes more dense, then liquid.  But they might not be solid in the middle.  more (later)

2.3.12 The moving molten iron generates a small magnetic field.  We can detect this with a magnetic compass, which points to the North Magnetic Pole (somewhere in northern Canada?) and South Magnetic Poles (somewhere in the Southern Ocean).  (These are not the same as the True North and South Poles.)  The Earth’s magnetic field pushes away some charged particles coming from the Sun – the solar wind (electrons and protons – and coming from space - cosmic rays (protons, helium++ and electrons), reducing radiation we would find harmful.  more (later)

2.3.13 The flow changes all the time so the magnetic poles are moving.  About every 30,000 years the flow changes so much the magnetic poles flip, so the magnetic north become the south and the magnetic south become the north.  (This doesn’t affect the daily rotation of the earth.)  When some minerals settle they line themselves up with the magnetic field and we can see traces of the changes.  more (later)

2.3.14 Earth’s atmosphere came Volcanoes spewing out gases and mid ocean vents.  into the atmosphere.  This was initially sulphur compounds, methane, hydrogen, carbon dioxide, ??  On smaller planets and our moon the gravity was not strong enough to keep the atmosphere.  Mars (a quarter of the size of the earth) still has some atmosphere but is still losing it, Mercury has lost all its atmosphere.  more (later)

2.3.15 As the Earth cooled, the water vapour in the atmosphere condensed and fell as rain, to form rivers, oceans and seas. The first rain lasted millions of years.  The lighter and higher surface rocks became islands and continents.  more (later) 

2.3.16 Different heat makes the winds.  Hot air expands and rises.  The land heats up more during the day and cools down more at night than the water.  So during the day hot air over the land rises and air flows onto the land from the sea.  At night the air flows the other way round.  The poles are cold and the equator is hot so air rises at the equator and flows to the poles where it sinks.  Air at the equator is moving around the earths axis at roughly the same speed as the ground is, but as the wind approaches the poles the ground is moving more slowly so the wind seems to be going faster around the axis, which is why we have prevailing westerly winds.  All these forces combine to make complex weather patterns.  more (later)

2.3.17 As rocks get hot during the day they expand, and at night they cool and contract, causing them to crack and break up.  Wind and water make smaller rocks tumble and chip off small bits.  Water flowing over or though rocks picked up some molecules like salt.  Rivers carried salt and silt to lakes and seas.  This made the oceans salty.  Where the silt settled on the bottom it formed sedimentary rocks.  more (later)

2.3.18 The moon rotating around the earth pulls the moveable bits of the earth towards it.  The water can move most easily, so we see daily tides.  The moon’s gravity is least on the other side of the earth, which allows the oceans to bulge out more, so many places get 2 high tides a day.  The sun’s gravitation also affects the tides.  When both the sun and moon are pulling in the same direction we get peak tides.  The moon’s and the sun’s gravity also stretches and squashes the earth itself.    more (later)

2.3.19 The molten rock below the surface moves up and down in convection currents as it cools. This causes the large rock continental plates on the surface to move (perhaps 10 centimetres per year), which is called plate tectonics.  When plates pull apart, a deep gap is generated, like the Atlantic Rift (which is near the surface in Iceland), and the Rift Valley in Africa.  When one plate pushes into another the plates crumple, or one goes above the other, and this generates mountains.  more (later) 

2.3.20 When plates move against each other they cause earthquakes, and earthquakes at sea shake the sea floor around and cause tsunamis (so called tidal waves). 

2.3.21 Flows of molten beneath the surface cause pressure and sometime blow as volcanoes.  The molten material that spews out forms igneous rocks.  Some regions called hot spots cause volcanoes to erupt at the same place even though the rocky surface – on land or sea - has moved over it.  We see these as a line of extinct volcanoes perhaps with an active one at the end, eg in the Hawaiian Islands.  A big one is due to blow sometime in the next few thousand years in America at Yellowstone National Park.  more (later)

2.3.22 Continents have moved around the earth, from the equator to the poles and back again.  About 1.1 billion years ago there was a supercontinent, which split into 3 main continents, which joined together again about 600 million years ago then split again, but these again joined together about 250 million years ago to form the supercontinent Pangaea, surrounded by a single ocean Panthalassa. 

2.3.23 Plate tectonics pulled Pangaea apart into Laurasia and Gondwana.  Laurasia split to form North America and Eurasia, with the Atlantic Rift between them.  Gondwana split to form South America, Africa, Antarctica and Australia.  As these continents moved, mountains formed on their leading edges – The Rockies and The Andes in North and South America, and The Great Dividing Range in Australia.  The European Alps forms as Africa moved north into Europe.  Other mountain ranges (such as The Urals) had formed as earlier continental plates collided.  A piece of Gondwana broke off and moved north-east, hitting Eurasia about 35 million years ago, to form India and the Himalaya Mountains.  more (later) 

2.3.24 Now the northern hemisphere has more land than the southern, and land heats more easily than water, so the world is actually about 2 degrees warmer in the northern summer than the southern summer, even though it is further from the sun at that time.  more (later)

2.3.25 The shape of the continents and the temperatures cause the ocean currents.  The Southern ocean began to flow around Antarctica after South America split northwards.  The Gulf Stream carries warm water from the equator to Europe where it mixes with ice from Greenland and the north pole, and gets cold, so it sinks and flows back to the equator.  The South Atlantic, Pacific and Indian oceans have their flows.  more (later)

2.3.26 The normal patterns of ocean currents, wind and rain and temperature and so on is called the climate.  This changes because the atmospheric changes.  Volcanoes or asteroids hitting the earth have put lots of dust in the air which keeps out sunlight causing the world’s climate to cool. The sun changes its behaviour, also affecting temperatures.  If the ocean currents change this will affect the winds, which affects rain and temperature.  Changes in the gases which make up the atmosphere can cause it to keep the heat in, like in a green house, and make the climate warmer.  more (later)

2.3.27 Eventually the radioactive material in the earths core will be used up, so no more heat will be produced so it will cool down, becoming solid all through, and Earth’s magnetic field will disappear.  The moon is getting further away from earth at 3-4 centimetres a year.  In about a billion years the Sun will be 10% hotter and water on earth will evaporate.  In about 5 billion years the Sun will turn into a Red Giant, and its surface will reach out to the Earth and the Moon and engulf them.  The outer layers of the Sun will fly off into space and the hot centre will slowly cool, over billions of years, as a “white dwarf” star until it is completely cold and solid.  more (later)

2.3.28 These processes could happen anywhere in the universe.  There are billions of galaxies, with billions of stars like ours.  Planets would form in the same way as our solar system.  Scientists can detect many large planets and are searching for earth-like ones.  Continents and seas and wind and rain might be found on them.  more (later)