Early Earth

Conditions on early earth

• High UV penetration due to no greenhouse gas effect

• Very little oxygen

• A lot of CH4 and CO2

• Very high temperatures

• Lightning, volcanic eruptions, etc.

Cells are the smallest units of life

They are the smallest units of self sustaining life - they can live on their own, they use energy to maintain order (MRHMGREN) cells can produce their own cells, cells can live outside of multicellular organisms

What is spontaneous generation

A thought that living things can spontaneously generate out of nowhere (eg. on early earth, life just appeared). This was falsified - news cells can only come from existing cells. Pasteur proved this wrong with his experiment where he used a swan necked bottle and boiled broth to prove that living things cannot generate from non living things, only smaller organisms. Tilting the broth allowed for dust etc. to enter, which formed bacteria, taking off the neck of course allowed bacteria to enter, but keeping neck safe and secure - no bacteria entered.

How did living material arise from non living material

Catalysis - small carbon compounds must form from inorganic compounds (eg. water, CO2, nitrogen, etc.) (eg. with ribozymes)

Self assembly - carbon compounds (eg. amino acids) must form together to make polypeptides. Also self assembly of the phospholipid bilayer

Compartmentalization - a membrane (the phospholipid bilayer) must form in water to ensure that cells have a barrier from other things and enclose the cell contents

Self replication of molecules - molecules must be able to self replicate to produce “offspring” or other.

The Miller Urey experiment

The Miller Urey experiment proved that life on earth did not arise from inorganic compounds, but organic compounds did. They did an experiment to mimick early life on earth.

The water in the globe was heated by fire to mimic the hot ocean (due to UV rays) of earth at that time. Water evaporated up to the gas chamber, which was filled with inorganic gasses found on early earth like CO2, H2, NH3, etc. There was also an electrical spark ignited for energy (as chemical reactions need energy to occur) which mimicked the lightning on earth at this time. Then, the products (if any) from this reaction travelled down a condenser to mimic rainfall, and were trapped in the little dip at the bottom. This process continued for about a week, when they extracted the cooled liquid at the bottom and found amino acids & other organic compounds.

Advantages and disadvantages of the M.U experiment

A: Proved that life on earth rose from inorganic → organic compounds

Conducted in a lab with rigorous tests etc.

D: Assumed the conditions on earth were those, no rock hard evidence at that time. Also, it only occured for a week when really, conditions on early earth occurred for centuries.

RNA as presumed first genetic material in first cell

RNA is much simpler than DNA, which makes sense for early cells.

RNA can self replicate AND store genetic information AND catalyze reactions using ribozymes

RNA mutates at a high rate (makes sense for first early cells because mutations cause genetic variation/diversity)

LUCA

Life evolved separately many times, but all living things today probably came from the same living thing. The last universal common ancestor. Eg. the genetic code is universal, all organisms use DNA and RNA, ribosome structure are similar. Only way to explain how all organisms on earth have same structure is if they came from the same common ancestor.