Earth is estimated at 4,500 millions years old - the oldest rocks are 4,000 million years old and the Earth has to be older than the rocks.
Erosion - The earths surface is made of rock layers. The oldest is at the bottom.The layers are compacted sediment, produced by weathering and erosion. Erosion changes the surface over time.
Craters - the moon's surface is covered with impact craters from meteors. Meteors also hit the earth but craters have been erased by erosion.
Mountain Formation - if new mountains weren't being formed the earths surface would have eroded to sea level.
Folding - some rocks look as though they've been folded in half, this required huge force over a long time.
How old is the Earth?
You can find out the Earths age by :
- Fossils of plants and animals in sedimentary rock layers, which show how lifes changed.
- the radioactivity of rocks. A rocks radioactivity decreases over time and radioactive dating measures radiation levels to find out a rocks age.
The structure of the Earth
Thin Rocky Crust -
- thickness varies between 10km and 100km
- oceanic crust lies beneath the oceans
- continental crust forms continents
The Mantle -
- Extends almost half way to the centre
- has a higher density and different composition than rock in the crust
- very hot, but under pressure
The core -
- Over half the Earth's radius.
- Made of nickel and iron and has a liquid outer part and a solid inner part.
- The decay of radioactive elements inside the Earth releases energy, keeping the interior hot.
- Was proposed by Wegener.
- Continents have a jigsaw fit, with mountain ranges and rock patterns matching up.
- fossils of the same animals on different continents.
- different continents had separated and drifted apart.
- when two continents collided they forced each other upwards to make mountains.
Geologists wouldn't accept Wegeners idea because
- he wasn't a trained geologist and was seen as a outsider
- supporting evidence was limited
- it could be explained more simply, for example a bridge connecting the continents eroded over time.
- the movement of the continents wasn't detectable.
Evidence from sea floor spreading proved Wegener's theory was correct.
The earth's crust is cracked into several large pieces called tectonic plates. The plates float on the Earth's mantle as they're less dense, can move apart, towards or slide past each other.
The lines where plates meet are called plate boundaries. Volcanoes, earthquakes and mountain formations normally occur at these plate boundaries.
Earthquakes near coastlines or at sea can often result is a Tsunami.
A geo-hazard is a natural hazard for example floods and hurricanes. Some have warning signs which give authorities time to evacuate the area, use sandbags etc.
However, others strike without warning so precautionary measures need to be taken. For example:
- buildings in earthquake zones are designed to withstand tremors
- authorities will often refuse planning permission in areas prone to flooding.
The mantle is fairly solid just below the Earth's crust. Further down it is liquid.
Convection currents in the mantle cause magma to rise. The currents move the solid part of the mantle and the tectonic plates.
Where the plates are moving apart, magma reaches the surface and hardens, forming new areas of oceanic crust and pushing the existing floor outwards.
New crust is continuously forming at the crest of an oceanic ridge and old rock is pushed out, this causes sea floors to spread by approximately 10 centimetres every year.
Earth has a magnetic field. It changes polarity every million years. Combined with the sea floor spreading, this produces rock stripes of alternating polarity. Geologists can see how quickly crust is forming by the width of the stripes. This occurs at constructive plate boundaries where plates are moving apart.
When oceanic and continental plates collide, the denser oceanic plate is forced under the continental plate. This is subduction. The oceanic plate melts and molten rock can rise to form volcanoes. This occurs at destructive plate boundaries.
Mountain ranges form along colliding plate boundaries as sedimentary rock is forced up by the pressure created in a collision.
Plate tectonics continued.
Earthquakes occur most frequently at plate boundaries
- The plates slide past each other or collide.
- The pressure builds up as plates push on each other
- Eventually, stored energy is released and waves of energy spread from the epicentre.
Plate movement is crucial in the rock cycle
- Old rock if destroyed through subduction
- Igneous rock is formed when magma reaches the surface
- Plate collisions can produce high temperatures and pressure, causing the rock to fold.
- sedimentary rock becomes metamorphic rock.
The solar system
The solar system was formed about 5000 million years ago.
- The solar system started as dust and gas clouds, pulled together by gravity.
- This created intense heart. Nuclear fusion began and the Sun was born.
- The remaining dust and gas formed smaller masses, which were attracted to the sun.
Smaller masses in our Solar System are
- Planets - nine large masses that orbit the Sun.
- Moons - small masses that orbit planets.
- Asteroids - small, rocky masses that orbit the Sun.
- Comets - Small, icy masses that orbit the sun.
Planets, moons and asteroids all move in elliptical (slightly squashed circular) orbits.
Comets move in highly elliptical orbits. Earth takes one year to make a complete orbit.
The sun is only 5000 million years older than the Earth.
The suns energy comes from nuclear fusion:
- Hydrogen atoms fuse together to produce an atom with a larger mass i.e. a new chemical element.
- Trapped energy in hydrogen atoms is released.
All the chemical elements larger than helium were formed by nuclear fusion in earlier stars.
It is the nuclei of hydrogen atoms that fuse together during nuclear fusion.
The universe is much older than the Sun, approximately 14,000 millions years old.
Our star - the sun, 100 times wider than Earth.
Our planet - the Earth, 12,800km in diameter.
Our galaxy - the Milky Way, 100,000 light years across containing at least 200 billion stars.
The Universe - contains billions of galaxies, with vast distances between them.
The speed of light.
Light travels at very high but finite (limited) speeds. If the distance is great enough, light speed can be measured.
The speed of light it 300,000 km/s (around 1 million times faster than sound). Light from earth takes just over 1 second to reach the Moon.
Sunlight takes 8 minutes to reach Earth. When we look at the Sun we see it as it was 8 minutes earlier.
Vast space distances are measures in light years. One light year is the distance light travels in one year (9500 billion km)
The nearest galaxy to the Milky Way is 2.2 million light years away.
Measuring distances in space
Distances are measured in two ways
- Relative brightness - the dimmer a star, the further away it is. However brightness can vary so a star's distance is never certain.
- Parallax - if you hold a finger at arms length and close each eye in turn, your finger appears to move. The closer your finger, the more it seems to move. Parallax uses this idea to work out distance. Stars in the near distance appear to move against the background of distance stars. The closer they are, the more they appear to move. The further the star, the less accurate the measurement is.
Radiation from stars tells us what we know about the. Types of radiation that stars produce include visible light, ultraviolet and infra-red. Light pollution is when electric lights on Earth make it difficult to see the stars. The Hubble Space telescope orbits at a height of 600km, so it is not affected by this.
The life cycle of a star
All stars consist of hydrogen and have a finite life
When a stars hydrogen supply eventually runs out, it swells and becomes colder.
It forms a red giant or a red super giant depending on it's size.
If a source of light is moving away from us, the wavelengths of light are longer than if the source is stationary.
Wavelengths of light from nearby galaxies are longer than the scientists expect. This means the galaxies are moving away from us.
Observations made by Edwin Hubble showed that almost all galaxies are moving away from us an the further away they are, the faster they are moving away. He developed this into Hubble's Law which states
The speed of at which a galaxy is moving away is proportional to its distance
If all the galaxies are moving away from us this must mean that space is expanding.
The beginning and the End
The big bang theory says that the universe began with a huge explosion 14,000 million years ago. The future of the universe depends on its amount of mass. Measuring the amount of mass is difficult so its fate is hard to predict. If there isn't enough mass the universe will keep expanding. If there's too much mass, gravity will pull everything back together and the Universe will collapse.
In 1996 a Mars meteorite appeared to contain an ancient alien fossil. Different explanations were offered but the debate still goes on.
If there are other life forms in the Universe they are likely to be on other planets or moons. Astronomers have detected some stars which orbiting planets. There's no confirmed evidence of alien life. Many scientists think that with the vast number of stars and galaxies, it's unlikely that only Earth has life.
What killed the dinosaurs?
Evidence shows that dinosaurs became extinct around 65 million years ago. One explanation is that an asteroid hit Earth.
- Fossils shows that dinosaurs gradually died out
- The chances of a large asteroid hitting earth are very small
- If an asteroid did hit earth, everything in the impact zone would be destroyed.
- Large asteroids have hit earth in the past. The Chicxulub crater in Mexico provides evidence of this. Scientists estimate the energy of this asteroid on impact was 10,000 times greater than all the world's weapons combined.
- A layer of iridium is found all over earth.
- The layer of iridium could be the result of an asteroid collision.
- a big asteroid would have caused firestorms, shock waves and possible climate change, dinosaurs couldn't of survived.
- The collision could have released sulfur and caused strong acid rain for weeks.
- Dust could have blocked the Sun and caused plants to die, affecting the whole of the food chain.
A good scientific explanation will provide reasons for all of the data. Many explain some facts, but not all of them.
Facts and explanations could be used to evaluate whether an asteroid could destroy the human race.
Unlike the dinosaurs, humans have the technology to detect asteroids, but that doesn't mean we would be able to stop or survive the impact.