Varför tror inte fler på utomjordiskt liv?

Olivine from Martian meteorite Allan Hills (ALH) 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass. The inclusions are irregular in shape and range in size from ∼40 μm to submicrometer. Some of the inclusions are elongate and boudinage‐like. The olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite. The olivine exhibits a very limited range of composition from Fo65 to Fo66 (n = 25). The δ18O values of the olivine and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3‰ and are indistinguishable from each other within analytical uncertainty.

The mineral chemistries, O‐isotopic data, and textural relationships indicate that the olivine inclusions were produced at a temperature >800 °C. It is unlikely that the olivines formed during the same event that gave rise to the carbonates in ALH 84001, which have more elevated and variable δ18O values, and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine. The reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel. If the olivine was formed by either reaction during a postcarbonate heating event, the implications are profound with regards to the interpretations of McKay et al. (1996). Due to the low diffusion rates in carbonates, this rapid, high‐temperature event would have resulted in the preservation of the fine‐scale carbonate zoning, while partially devolatilizing select carbonate compositions on a submicrometer scale (Brearley, 1998a). This may have resulted in the formation of the minute magnetite grains that McKay et al. (1996) attributed to biogenic activity.

Och som du också Vet så har McKay och hans team både besvarat och motbevisat all kritik som rintats mot hans forskning.
Du vet naturligtvis också att Nasa aldrig avskedade McKay.

Ja, som sagt så har jag så svårt för att förstå hur så många som säger sig vara djupt intresserade av frågan om utomjordiskt liv ändå är så ointresserade av att själv försöka ta reda på hur det Faktiskt Förhåller Sig med "ditt eller Datt" (dvs vad folk påstår, och hur andra vill motsäga det).

Det Går ju faktiskt att själv läsa på om tex McKay, och därgenom själv bilda sig en uppfattning.
Istället för att bara rakt av svälja andras (eller hans) versioner av det.

Det kan naturligtvis finnas flera olika, mer eller mindre tänkbara, teorier till varför McKays resultat blev så illa åtgångna (samt han själv också faktiskt, det ska vi inte glömma. Han blev ju praktiskt taget persona non grata efter det).

2. We need better and more reliable biomarkers.

The problem with ALH 84001 is not the lack of potential biomarkers. It clearly has potential biomarkers including organic compounds (PAHs, amino acids, and kerogenlike forms), carbonates, magnetites, sulfides, and fossil-like forms. The problem is that we do not understand any of
these biomarkers well enough to be confident that the properties of these features in ALH 84001 truly indicate liferelated processes as opposed to strictly non-biologic processes. Are the minerals precipitated by strictly inorganic chemistry, or with the aid of living organisms or with the
aid of organic compounds derived from living organisms?
Are the PAHs and amino acids all derived from living systems or were they generated by inorganic processes? (This is a separate question from possible Antarctic contamination).
Are the fossil-like morphologies truly formed from microbes
and their products or are they formed by non biologic precipitation? Is the extreme carbon isotope fractionation a result of biologic processing? All of these features are present in ALH 84001. But do we understand their properties and occurrences well enough to be confident which are true
biomarkers and which are impostors? I think the answer is
no. Before we bring samples back from Mars we must have in a data base, a set of tested, reliable, and certified biomarkers with well-documented distinguishing properties so
that we can search for and describe these biomarkers in the returned samples and use them to unequivocally answer the question of whether or not there is evidence for life in these
Mars samples. We need to be confident that the biomarkers we use cannot be formed by any conceivable non biologic process. We also need to decide whether a single biomarker
is sufficient or whether we need several. Conversely, we need to decide whether the absence of known biomarkers is sufficient to eliminate the possibility of Mars life.

5. It is sometimes difficult to either prove or disprove a
hypothesis.
Our original hypothesis was that several observed features in ALH 84001 could all be reasonably explained by the presence of early life on Mars. This was a hypothesis
and the original paper was filled with qualifiers. The hypothesis was based on circumstantial evidence or scientific observations of several different types, and the hypothesis
seemed to explain all of the evidence with a single kind of event, namely the presence in the rock of microbial activity.
Many other investigators have been able to reproduce our original data, although a number of new kinds of data have been added by others to our original observations. Only in
one or two cases have completely contradictory data been reported.
Refuting one line of circumstantial evidence supporting a hypothesis (by either showing that the data were wrong or that the proposed explanation can be replaced by a clearly
better one) does not mean that the hypothesis is wrong, it simply means that that line of circumstantial evidence is incorrect. While it may weaken the case for the hypothesis,
it does not invalidate the hypothesis. Only when all proposed lines of evidence supporting a hypothesis are refuted can that hypotheses be considered to be wrong (and wrong
hypotheses may benefit scientific progress as much as right ones). A hypothesis can be also be considered wrong if none if its predictions are correct.
Conversely, the hypothesis can only be proven to be correct when either multiple kinds of circumstantial evidence become overwhelming, or a single line of evidence is so
strong that it cannot be explained by any alternate hypothesis — in other words, a smoking gun. A hypothesis can be greatly strengthened if its predictions are subsequently
shown to be true. In our view, the ALH 84001 hypothesis of early life on Mars is still valid and has neither been adequately refuted nor adequately proven. The people who propose a hypothesis are not necessarily responsible for proving it because they may not have the correct tools,
technical specialties, or samples, although they may have a moral obligation to either try to prove it or to refute it themselves. For ALH 84001 and the other Mars meteorites, the
question is still open, and may not be answered until martian samples are returned by a space mission.

All of these features are present in ALH 84001. But do we understand their properties and occurrences well enough to be confident which are true
biomarkers and which are impostors? I think the answer is no.

The problem is that we do not understand any of
these biomarkers well enough to be confident that the properties of these features in ALH 84001 truly indicate liferelated processes as opposed to strictly non-biologic processes.