Climate change over Earth history Flashcards
The solar nebula:
A bright disk-like cloud - the solar nebula from which the solar system forms. The nebula contains large amounts of hydrogen and helium gas. but also ‘dust’. Bright sports within the nebula are massive stars and in their nuclear powered hearts, heavier elements up to iron and nickel are being synthesised
Supernova explosion:
There is a blinding flash of light - a supernova explosion - the death throes of a massive and brightly burning, but very short-lived star. This explosion seeds to dust of nebula with even heavier elements. The explosion sends a shockwave through nebula, producing pockets that are denser with material. A central blob begins to coalesce - the beginning of a new star - our Sun. Around it swirling cloud of dust destined to become our solar system.
Only rocks from early earth that still survive with us today:
The only objects you can find on the earliest earth that are still with us today are tiny crystals of a mineral called zircon. Zircon grains are typically a few tenths of a millimetre in size and are very hard, so can survive after the rock in which they first formed has been weathered away. The single micro-crystals of zircon retain a chemical memory that enables us to date their origin precisely.
Late Heavy bombardment
To find sedimentary rocks you need to move forward another 200 million years which takes you through he interval of frequent and large meteorite impacts known as Late Heavy bombardment - this appears to be the final act in the genesis of the modern Solar System.
BIFs on earth
The BIFs you see being deposited could have been formed by an early evolved form of ‘anoxygenic’ photosynthesis different from the type of photosynthesis we are familiar with today - where Oxygen is liberated from the splitting of water.
Carbon
Carbon started life being synthesised in the heart of a giant star and probably came to the young earth riding on one of the meteorites that also supplied thae water. On Earth tha carbon atom takes the form of a molecule of CO2. Quite often it crosses the boundary between the atmosphere and the ocean and dissolves there, or goes back in the opposite direction, passing freely between the two
Carbon sink
The loss of carbon to sediments in a ‘sink’ - a leak that removes it from the surface where life can use it, and locks it up in the Earth. The leak is very small compared to the amounts that exchange between the air, oceans and living things.
Carbon however, doesn’t remain trapped in sedimentary rocks forever, because the rocks themselves are recycled, thanks to plate tectonics.
The Great Oxidation
About 2.4 billion years ago an irreversible change happens, the Earth never goes back to its past, oxygen-free atmosphere. ‘The Great Oxidation’ was a book written by Dick holland of Harvard University. It is likely the Earth was shrouded in a high altitude haze before the Great Oxidation. It would have been formed in the same way as the clouds that today we see enveloping the Solar System’s outer planets and moons.
Formation of ozone layer
Accompanying the appearance of oxygen is an ozone layer in the upper atmosphere.Ozone is three oxygen atoms combined in a single molecule - a supercharged oxygen molecule, fiercely reactive, and generated by the action of UV radiation on ‘ordinary’ oxygen molecules.
As ozone layer begins to form in the upper reaches of the atmosphere as soon as more than a few parts per million of oxygen are present, and once in place it blocks the further passage of UV to the surface.
