In Jain dharma we have to carefully separate three things:

1. Time (kāl)
2. The universe (loka) and its regions
3. This particular planet / era that we call “earth” or Bhārat Kṣetra in the present Avasarpiṇī

1. Is time infinite?

Yes. Time (kāl) is a separate eternal substance (dravya). It has:

• No beginning and no end
• Endless cycles (kāl‑chakra) of Utsarpiṇī (ascending) and Avasarpiṇī (descending) eras, repeating forever .

So “infinite time” does not mean any particular world, star, or planet is infinite. Only time itself is infinite.

2. Is “earth” (our current world‑situation) infinite?

No.

In Jain cosmology:

• The universe (loka) as a whole is beginningless and endless, but
• Specific regions and conditions within it go through cycles.

Our “earth” in Jain terms is Bhārat Kṣetra of Jambūdvīpa in the middle world (madhya‑loka). Here:

• Time is currently in Avasarpiṇī, 5th era (Duḥṣamā) – a spiritually weak period.
• In this half‑cycle and this region there are exactly 24 Tīrthaṅkars, from Ṛṣabhadev to Mahāvīr Swāmī .

But this does not mean:

• This particular arrangement of continents, oceans, sun, etc. is “eternally the same” in the way modern astronomy describes.

Jain texts speak in their own cosmological language, not in NASA terms. They describe a fixed cosmic structure, but the conditions of beings, lifespan, religion, etc. in that structure keep changing.

So: time is infinite, the overall universe is without beginning and end, but particular formations and situations are temporary and cyclical, not “infinite objects”.

3. Where do Tīrthaṅkars arise, if time is infinite?

Key Jain points:

1. 24 Tīrthaṅkars per half‑cycle per suitable human region (like Bhārat Kṣetra).

- Each Utsarpiṇī and each Avasarpiṇī in Bhārat Kṣetra has 24 Tīrthaṅkars – no more, no less. - Same pattern applies to other suitable regions (Mahāvideh Kṣetra, Airāvat Kṣetra, etc.) .

1. Infinite cycles + many regions = infinite Tīrthaṅkars overall.

Because: - Time cycles are infinite, - There are many kṣetras where humans and dharma can exist, therefore, innumerable souls become Tīrthaṅkars across infinite time, but in any one half‑cycle of one such region you only see 24.

1. Not limited to “our current earth” or our current human history.

- Before this Avasarpiṇī, in past cycles, there were other sets of 24 in Bhārat Kṣetra. - Right now, even though no Tīrthaṅkar is present in our Bhārat Kṣetra, there are Tīrthaṅkars at the same time in Mahāvideh Kṣetra, such as Śrī Simandhar Swāmī (according to Jain tradition). - In future Utsarpiṇī, another 24 will again arise in Bhārat Kṣetra.

So Tīrthaṅkars are not tied only to this one phase of our planet’s history. They appear:

• In different time periods (past, present in other kṣetras, future)
• In different world‑regions within the Jain cosmos

4. What about “before the earth formed” or “after the sun engulfs earth”?

Those phrases come from modern cosmology (Big Bang, stellar evolution). Jain scriptures do not describe creation or destruction of the universe in that way. Instead they say:

• The universe is eternal (no first moment, no final collapse).
• Within it, conditions, bodies, continents, lifespans, etc. change in endless up‑and‑down cycles.

So from a Jain standpoint:

• It is not that “no Tīrthaṅkar could exist before our earth formed” – rather,
• In other beginningless cycles and other regions, there were already Tīrthaṅkars and liberated beings.
• In the far future, even if the physical picture of our solar system changes, the soul‑journeys and Tīrthaṅkar‑hood continue in accordance with the eternal kāl‑chakra and the karmas of jīvas.

5. Do Tīrthaṅkars ever take non‑human forms?

For both Digambar and Śvetāmbara traditions:

• A Tīrthaṅkar’s last birth (the one in which they attain Keval‑jñān and establish the fourfold saṅgha) is always in human form, in a special, highly developed human body, in a suitable kṣetra.
• Before that final human life, they may have countless past lives in all kinds of gatis (heavenly, animal, even hellish), but Tīrthaṅkars as Tīrthaṅkars are humans, not animals or devas.

So the Jain answer to your question, in simple form:

• Time is infinite, but that does not make this particular earth or this physical setup infinite.
• Tīrthaṅkars are not confined to this one tiny slice of cosmic history.
• They arise, again and again, in different eras and different human regions of the eternal universe, always as humans, according to fixed laws of the time‑cycle and karma.