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Author Topic:   A very brief history of Life
Member (Idle past 1523 days)
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Message 1 of 3 (798272)
02-01-2017 1:41 PM

The oldest fossil record of life we currently have is over 3.5 billion years old.
Earliest evidence for life on Earth
The earliest identified organisms were minute and relatively featureless, and their fossils look like small rods, which are very difficult to tell apart from structures that arise through abiotic physical processes. The oldest undisputed evidence of life on Earth, interpreted as fossilized bacteria, dates to 3 Ga.[52] Other finds in rocks dated to about 3.5 Ga have been interpreted as bacteria,[53] with geochemical evidence also seeming to show the presence of life 3.8 Ga.[54] However, these analyses were closely scrutinized, and non-biological processes were found which could produce all of the "signatures of life" that had been reported.[55][56] While this does not prove that the structures found had a non-biological origin, they cannot be taken as clear evidence for the presence of life. Geochemical signatures from rocks deposited 3.4 Ga have been interpreted as evidence for life,[52][57] although these statements have not been thoroughly examined by critics.
The cyanobacteria have an extensive fossil record. The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old!
Cyanobacteria are among the easiest microfossils to recognize. Morphologies in the group have remained much the same for billions of years, and they may leave chemical fossils behind as well, in the form of breakdown products from pigments. Small fossilized cyanobacteria have been extracted from Precambrian rock, and studied through the use of SEM and TEM (scanning and transmission electron microscopy).
At right is a layered stromatolite, produced by the activity of ancient cyanobacteria. The layers were produced as calcium carbonate precipitated over the growing mat of bacterial filaments; photosynthesis in the bacteria depleted carbon dioxide in the surrounding water, initiating the precipitation. The minerals, along with grains of sediment precipitating from the water, were then trapped within the sticky layer of mucilage that surrounds the bacterial colonies, which then continued to grow upwards through the sediment to form a new layer. As this process occured over and over again, the layers of sediment were created. This process still occurs today; Shark Bay in western Australia is well known for the stromatolite "turfs" rising along its beaches.
In some cases, the stromatolites were infiltrated with a mineral-rich solution which fossilized the bacteria along with the layers, but more often only the layers are preserved.
The oldest stromatolites date to the Early Archaean, and they became abundant by the end of the Archaean. In the Proterozoic, stromatolites were widespread on earth, and were ecologically important as the first reefs. By the close of the Proterozoic, the abundance of stromatolites decreased markedly, though cyanobacteria continued to leave a fossil record, such as Langiella and Kidstoniella known from the Lower Devonian Rhynie chert.
The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth's history. The oxygen atmosphere that we depend on was generated by numerous cyanobacteria photosynthesizing during the Archaean and Proterozoic Era. Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today.
While contemporary cyanobacteria are linked to the plant kingdom as descendants of the endosymbiotic progenitor of the chloroplast, there are several features which are unique to this group.
Carbon fixation
Cyanobacteria use the energy of sunlight to drive photosynthesis, a process where the energy of light is used to split water molecules into oxygen, protons, and electrons. Because they are aquatic organisms, they typically employ several strategies which are collectively known as a "carbon concentrating mechanism" to aid in the acquisition of inorganic carbon (CO2 or bicarbonate). Among the more specific strategies is the widespread prevalence of the bacterial microcompartments known as carboxysomes.[15] These icosahedral structures are composed of hexameric shell proteins that assemble into cage-like structures that can be several hundreds of nanometers in diameter. It is believed that these structures tether the CO2-fixing enzyme, RuBisCO, to the interior of the shell, as well as the enzyme carbonic anhydrase, using the paradigm of metabolic channeling to enhance the local CO2 concentrations and thus increase the efficiency of the RuBisCO enzyme.[16]
Metabolism and organelles
As prokaryotes, cyanobacteria do not have nuclei or an internal membrane system. In most forms, the photosynthetic machinery is embedded into folds of the external cell membrane, called thylakoids. Cyanobacteria get their colour from the bluish pigment phycocyanin, which they use to capture light for photosynthesis. In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide[18] a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria. Carbon dioxide is reduced to form carbohydrates via the Calvin cycle.[citation needed]The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria.[citation needed]
The first life thus is >3.5 billion years old, and it was likely even simpler than the prokaryote cyanobacter shown above.
Since that time the only way that life has been observed to reproduce and diversify in single cell life forms is by mitosis (cell division), with occasional Horizontal gene transfer.
Then some 1.6—2.1 billion years ago ago eukaryotes appeared
Origin of eukaryotes
Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). These act as sex cells (gametes — each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes) resulting from genetic recombination during meiosis.
The origin of the eukaryotic cell is considered a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine; Knoll (2006) suggests they developed approximately 1.6—2.1 billion years ago. Some acritarchs are known from at least 1.65 billion years ago, and the possible alga Grypania has been found as far back as 2.1 billion years ago.[69] The Geosiphon-like fossil fungus Diskagma has been found in paleosols 2.2 billion years old [70]
Hypotheses for the origin of eukaryotes
Different hypotheses have been proposed as to how eukaryotic cells came into existence. These hypotheses can be classified into two distinct classes — autogenous models and chimeric models.
Autogenous models
Autogenous models propose that a proto-eukaryotic cell containing a nucleus existed first, and later acquired mitochondria.[95] ...
Chimeric models
Chimeric models claim that two prokaryotic cells existed initially — an archaeon and a bacterium. These cells underwent a merging process, either by a physical fusion or by endosymbiosis, thereby leading to the formation of a eukaryotic cell. ...
All multicellular life involves eukaryotic cells, and they appear to be monophyletic, descendant from a single cell.
In sexual reproduction the process is a little more complicated than mitosis
Meiosis Listeni/maɪˈoʊsᵻs/ is a specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them.[1] ..
In meiosis, DNA replication is followed by two rounds of cell division to produce four potential daughter cells, each with half the number of chromosomes as the original parent cell. ...
Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, with successive generations maintaining the same number of chromosomes. For example, diploid human cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes (46 total), half of maternal origin and half of paternal origin. Meiosis produces haploid gametes (ova or sperm) that contain one set of 23 chromosomes. When two gametes (an egg and a sperm) fuse, the resulting zygote is once again diploid, with the mother and father each contributing 23 chromosomes. This same pattern, but not the same number of chromosomes, occurs in all organisms that utilize meiosis.
There is no new "creation of life" or added material observed through either mitosis or meiosis reproductive mechanisms, it is just a flowing of life from parent to offspring, a continuous flow that has been going on for over 3.5 billion years.
Thus the pro-life claim that "life is created at conception" is factually flawed misinformation.
Edited by RAZD, : .

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 Message 2 by RAZD, posted 02-03-2017 4:57 PM RAZD has seen this message but not replied

Member (Idle past 1523 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004

Message 2 of 3 (798597)
02-03-2017 4:57 PM
Reply to: Message 1 by RAZD
02-01-2017 1:41 PM

The pro-life claim "life is created at conception" is just wrong
There is no new "creation of life" or added material observed through either mitosis or meiosis reproductive mechanisms, it is just a flowing of life from parent to offspring, a continuous flow that has been going on for over 3.5 billion years.
Thus the pro-life claim that "life is created at conception" is factually flawed misinformation.
Exploring this further:
Human Development Chart:
sperm & ovum form Zygote - single cell capable of growth into a human being
zygote lasts 30 hours, then makes first division
morulla or blastula up 5days ball of undifferentiated totipotent cells
Blastocyst by day 5 Hollow Ball of cells, external and internal different. ca. 100 cells inner 50 are pleuripotent stem cells. External will become placenta, internal will become embryo
day 7 - 9 Blastocyst implants in wall of uterus
(55% of Zygotes never reach this stage.)
day 14 - 16 Blastocyst develops line of dark cells down centre that will become the spinal chord. Real differentiation has begun.
Embryo day 14
to week 8
Embryonic phase:
day 30 Lengthens and differentiates into
ecto-, meso-, & endo derm
Embryonic phase ends week 8 At this point enough development to call a foetus. All organs and structures found in a newborn infant are now present.
foetus week 9- 12 Major organs have begun to develop. Recognizably human, but cannot survive outside the womb.
15 % of pregnancies miscarry during weeks 4-12
foetus week 24 About 11 inches long and weighs about 1lb 10 oz.
foetus weeks 29 - 39 Most healthy foetuses delivered during this period survive, earlier ones may need mechanical help to survive.
birth of baby week 39
child 8 - 11 yrs Capable of independent survival

bold for emphasis.
So a zygote is "capable of growth into a human being" ... except that 55% never reach day 9, implanting in wall of uterus. That is more than half of zygotes are not "capable of growth into a human being" and of the 45% that do proceed to week 12, 15% miscarry, meaning that 55% + 15%x45% = 62% leaving only 38% of the original zygotes with any hope of growing into a living breathing human being.
Miscarriages continue to occur right up to birth, including premature birth and still-birth. A still-born fetus has no hope of growing into a living breathing human being. Furthermore ...
Blighted Ovum: Symptoms, Causes and Prevention
A blighted ovum (also known as anembryonic pregnancy) happens when a fertilized egg attaches itself to the uterine wall, but the embryo does not develop. Cells develop to form the pregnancy sac, but not the embryo itself. A blighted ovum occurs within the first trimester, often before a woman knows she is pregnant. A high level of chromosome abnormalities usually causes a woman’s body to naturally miscarry.
One of the first things you need to know if you have been diagnosed with a blighted ovum is that this is a loss. Give yourself time and permission to grieve. This is a type of miscarriage, and you can help yourself in the grieving process by learning more about surviving a miscarriage.
A blighted ovum is the cause of about 50% of first trimester miscarriages and is usually the result of chromosomal problems. A woman’s body recognizes abnormal chromosomes in a fetus and naturally does not try to continue the pregnancy because the fetus will not develop into a healthy baby. This can be caused by abnormal cell division, or poor quality sperm or egg.
There was never any hope that the zygotes that ended up as empty sac pregnancies could have grown into a living breathing human being, and these are fairly common among miscarriages.
What to Know About Ectopic Pregnancy
For pregnancy to happen, the ovary has to release an egg into the fallopian tube, where it stays for about 24 hours. There it has to come in contact with a sperm to be fertilized. The fertilized egg stays in the fallopian tube for 3 or 4 days before it heads to the uterus. There it attaches to the lining and continues to grow until a baby is born.
But if the fertilized egg implants in your fallopian tube or somewhere else in your abdomen, you end up with what’s called an ectopic pregnancy. In these cases, the pregnancy can’t continue normally, and it requires emergency treatment.
These pregnancies require medical intervention to prevent the death of the woman, whether or not you call it abortion, and (not trying to be insensitive, just factual) there is no hope of these types of pregnancy ever becoming a living breathing human being. So there should be no objection to this medical intervention.
And there is more information pertinent to the issue of actually resulting in a living breathing human being ...
Premature babies' disability risk
Forty per cent of very premature babies have significant learning disabilities, ...
The programme has had exclusive access to the unpublished Epicure study, the largest study of its kind.
Just over 1,200 were born alive and 811 were admitted to a neonatal intensive care unit. Of these 314 survived to go home.
The first phase of the study revealed at two and a half years old 50% of those studied had some form of disability.
In a quarter of the children severe disabilities were identified, including cerebral palsy, blindness, deafness and arrested development.
The latest results show that 40% of the surviving children had moderate to severe problems in cognitive development at the age of six, compared to 2% of a control group of their classmates.
But Professor Kate Costeloe, Prof of Paediatrics, Queen Mary, University of London, who also worked on the study said: "I would hope that people understand that being born early is a very, very serious business, that survival is not high, and that should children survive, their likelihood of having life-long problems - particularly in respect of learning is high.
"At 23, 24 weeks I have sometimes thought that if these outcomes are as good as they can be, should we be doing this."
Bright Asamany, born at 24 weeks, is one of the most severely disabled of all the children who were born in 1995 ... his father, Kennedy, says ... if they had another baby born as early as Bright, he would say "turn off the machine, there is no need to continue".
Check the table above for where 24 weeks fits in the development of the foetus, as this appears to be the lower limit of premature birth that can survive with medical assistance, even if the quality of life is severely diminished -- and some parents may justifiably choose to turn the machine off.
And that should be their right to choose, just as family has the right to choose to turn off the machines at the end of life for terminally ill parents.
But what is indisputable is that over 62% of conceptions have no hope of ever becoming a living breathing human being. That is not "creation" of life.
Edited by RAZD, : .
Edited by RAZD, : ..

we are limited in our ability to understand
by our ability to understand
... to learn ... to think ... to live ... to laugh ...
to share.

Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 1 by RAZD, posted 02-01-2017 1:41 PM RAZD has seen this message but not replied

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Message 3 of 3 (798640)
02-04-2017 7:12 AM

Thread Copied to Creation/Evolution Miscellany Forum
Thread copied to the A very brief history of Human Life thread in the Creation/Evolution Miscellany forum, this copy of the thread has been closed.

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