Origin of life and its beginings on Earth. Disclosure 33
The origin and beginning of life on Earth are two independent events. Good few details are known about them but, far from clarifying the origin of life, they open new questions that we are not yet able to answer completely.
We will start pointing out the most relevant 11 phenomenon about the beginning of life, as we know it, on Earth.
1. 5000 years ago, about 8700 years after the Big Bang, a portion of materia condensed and subsituted a protosolar nebula consisting of a central sphere orbited by much smaller masses.
2. 4600 years ago a nearby star became a supernova and its explosion sent a shock wave that increased the angular moment of the protosolar nebula. In consequence, the nebula increased its rotation, flattened becoming a protoplanetary disk perpendicular to the rotation axis, and the increase in collisions grouped the material forming protoplanets.
The increase in temperature in the center of the disk, the beginning of the nuclear fusion (from hidrogen to helium), and its contraction, originated the T Tauri star that we know as The Sun.
3. 4570 million years ago, at 150 million Km from the protoplanetary disk centre, a protoplanetary ring was formed, made of dust and pieces that ended up crashing and gathering under the effect of the solar wind and gravity, giving origin to planet Earth.
With this phenomena starts the Earth’s geological history, with a period named Precambrian, that would last until 560 million years ago. During this Precambrian period (from -4570 to -560 million years) were given those events relative to the beginning of life, even though the most important ones are given between -4150 and -1700 million years as we will see next.
4. 4150 million years ago physical conditions for water condensation were given and probably appeared the first autoreplicative molecules, known as primitive RNA. This hypothesis, called The RNA world hypothesis, suggests that this molecule was the first life form on Earth that at some point found accommodation inside a membrane. The opposite hypothesis considers that with the availability of liquid water membranes could be formed (known from Oparin as coacervates previous to RNA, that later hosted genetic material.
Both coacervates and RNA are previous to DNA, proteins and cells.
5. 3900 million years ago appear the first prokaryotic simple cells. They consist of a symbiosis of a membrane with the genetic material and the ribosomes (small particles able to produce proteins). Each ribosome has a small subunit, the one that joins the RNA, and a big subunit, which cathalyses the peptidic bonds formation. These subunits consist of specific ribosomic RNA and specific proteins. They are synthesized in the nucleolus.
6. 3860 million years ago, in another planet consisting of another protoplanetary ring, Mars, a similar phenomenon occured and some simple cells developpe and leave microfossils in Martian rocks.
One of this rocks came off Mars, as a consequence of an impact, 16 million years ago and after travelling through the interplanetary space impacted in the Antarctica 13000 years ago.
This meteorite is known as ALH 84001 and it brings us news about a Martian biological phenomenon, contemporaneous to the terrestrial one, for which appear in both planets the first procariote simple cells.
7. 3800 million years ago, the massive meteorites bombing stops, as well as the material exchange between the Solar System planets and between the planets and the rests from the primitive protoplanetary disk.
8. 3600 million years ago the first bacteria and stromatolites appear, from which we have complete fossil evidence.
9. 3460 million years ago the first cyanophytic bacteria appear, from wich we have fossil evidence in Apex (Australia)
10. 1850 million years ago, endosymbiosis between simple prokaryotic cells occurred and this originated a complex type of cells called eukaryotic cells. These new cells consist of a membrane, genetic material, ribosomes and organelles. The organelles have their own intern membrane and they are considered to have been simple cells that breathed oxygen or that performed photosynthetic functions. Prokaryotic simple cells which used oxygen were included, by endosymbiosis, inside other simple cells and became mitochondrias. Other prokaryotic photosynthetic cells were included, also by endosymbiosis, inside other simple cells and became chloroplasts.
11. 1700 million years ago, multicellular organisms appear by means of association of eukaryotic cells which specialize and differenciate giving tissues and organs.
As we said at the beginning of this blog “The origin of life and its beginings on Earth are two independent events. Good few details are known about them but, far from clarifying the origin of life, they open new questions that we are not yet able to answer completely”.
In the second part of this blog we will develop some partial answers to the questions that we have:
1. What’s the origin of the primitive RNA?
2. What’s the origin of the material that built membranes and primitive coacervates?
3. Did life appear on Earth contemporaneusly to other places or did it come from other places?
4. What influence had the formation of organic material contained in the interstellar dust, which came from the protosolar nebula, on the origin of life on Earth?
5. What influence had the interplanetarial exchanges of organic material realized through meteorites that came massively from -4570 to -3800 million years?