in the Srimad Bhagavatam 1.1.4
It says quote:
Once, in a holy place in the forest of Naimiṣāraṇya, great sages headed by the sage Śaunaka assembled to perform a great thousand-year sacrifice for the satisfaction of the Lord and His devotees.
how come they could do a sacrifice that would last so long?
It is said that people used to live longer in other yugas but as I understand this is already Kali Yuga.
Irrespective of the yuga, it is simply impossible for a single human being to perform a thousand-year yajña.
"sahasra-samam" or "1000 years" in the context of yajñas should be interpreted as 1000 days. This is what Ganganath Jha says summarizing the Pūrva Mīmāṁsā arguments on this topic:
VISHVAJIT SACRIFICE
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Whenever the Veda enjoins the giving away of 'unmeasured wealth', it is only much wealth that is meant. (Sū. 6.7.22); and it should be taken definitely as standing for 'more than a thousand' gold-pieces. (Sū. 6.7.23–25.)
Similarly, when a sacrifice is enjoined as to be performed 'for a thousand years', it is to be taken as standing for a thousand days (Sū. 6.7.31–40.). In connection with this, several interpretations have been suggested in the Sūtras as Prima Facie View:
That the thousand-year sacrifice is really performed for a thousand years, and is meant for performers who are superhuman;
It should be performed for a thousand years, and by human beings,—but by several generations;
'Thousand Years' stands for thousand months.
All this has been rejected; the accepted view being that 'years' stands for days.
Śabara in his commentary says there are limits to what the human body can physically do despite practice and the availability of medicines.
Also, the idea of human beings living for 1000 years goes against Śruti injunctions like Shatāyurvai puruṣah ('a man's life extends to a hundred years') so a literal interpretation does not work in this case.
ADHYĀYA VI, PĀDA VII, ADHIKARAṆA 13: The term 'thousand years' stands for 'thousand days'.
Sūtra (31).
[Pūrvapakṣa (A)—continued]—"The 'thousand-year sacrifice' must be taken as being for those whose life-span is of that extent,—it being impossible for human beings.”
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Sūtra (32).
[Pūrvapakṣa (A)—concluded]—"There is a commendatory text which already indicates that the performers of the sacrifice are beings other than human.”
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Sūtra (33).
[Pūrvapakṣa (B)]—"Or, it must be meant to be performed by human beings, as it is their sphere of activity."
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Sūtra (34).
[Refutation of Pūrvapakṣa (B)]— That cannot be; because they do not possess that capacity.
Bhāṣya.
No medicines have been found to possess the capacity of prolonging life to the extent of a thousand years. All that they are capable of doing is—the improving of digestive powers, the removal of wrinkles and grey hair, the improving of voice and complexion and the resuscitation of memory;—they are never found to bring about longevity.—"From the improvement of voice and complexion and other signs, we shall infer a longer life also."— That is not possible, we say.—"Why?"— Because there is the text declaring that 'a man's life extends to a hundred years' ('Shatāyurvai puruṣah'); and this would not be true if a man were to live longer.—"We may expound the compound word 'Shatāyu' as 'Shatāni āyuḥ yasya', 'one whose span of life extends over hundreds of years'."—Numerals are not compounded in this fashion; nor are they expressive (even when formed). The learned people have also declared that 'there can be no compounding of words with the dual or the plural endings'.
Sūtra (35).
[Further refutation of Pūrvapakṣa (B)]—Also because no connection has ever been perceived.
Bhāṣya.
Never have medicines ever been found to be connected with such longevity (as extends over a thousand years); and until such a connection has been actually perceived there can be no inference from it,—"There could be an inference from general premises: Medicines are actually found to bring about smaller degrees of stability, and it stands to reason that, if they were repeatedly taken, they would become more and more effective and would bring about a permanent stability in the body. Though there is the declaration 'The man's life-span extends to a hundred years', yet we find people actually living longer than that."
The answer to this is as follows:—
The premiss suggested is not true beyond doubt; even though it may be that the medicines used bring about all that is possible in the way of the stability of the body, even to such an extent as has never before been perceived;—for instance, when walking, people may attain all the speed possible, but by mere repetition they could not proceed even four miles, during the whole of their human life. So that in the case in question, as there would be no connection (between the medicines and longevity), it would always be open to doubt whether or not people (using the medicines) would secure longevity; and if this remains doubtful, there can be no inference from that premiss; and in the matter of imperceptible things, nothing can be accepted without sufficient proof.—From all this it is clear that without doubt there are no persons living so long (as a thousand years),—and this is what has been asserted regarding human beings.
Question—"What then does the text mean?"
[In answer we have the following Sūtra, which sets forth the third Pūrvapakṣa view.]
Sūtra (36).
[Pūrvapakṣa (C)]—"What is laid down should be regarded as a 'Function for Generations',—says Kārṣṇājini; as it is impossible for a single man."
Sūtra (37).
[Refutation of Pūrvapakṣa (C)]—In reality, inasmuch as the entire performance should be connected with a single performer, the performance of the sacrifice should be done by a single person.
Bhāṣya.
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Question—"What then is the meaning?"
Answer—It is as follows:—
Sūtra (38).
There being mutual inconsistency, one of the two terms must be taken in the indirect figurative sense,— says Lābukāyana.
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Sūtra (39).
It is the term 'year' that should be taken in an indirect figurative sense; because it is something variable.
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Sūtra (40).
[Pūrvapakṣa (D)]—"That word ('saṃvatsara', 'year') should be taken as in the case of the archetype; because that is what should be applicable here."
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Sūtra (41).
[Final Siddhānta]—In reality, the term should be taken as standing for 'days', as it is the number of days that are referred to (in the term 'trivṛt').
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