Recent comments in /f/askscience

haysoos2 t1_j6bp1f2 wrote

Reply to comment by LaRoara42 in Shouldn't goldilocks zones shift over time? by LaRoara42

Not really. Our entire biology and fossil history fits with the diversity of life in Earth.

As multicellular, deuterostome, bilateral, chordate vertebrates, osteichthyans, sarcoptergyians, tetrapods, synapsids, mammals, eutherians, primates, cercopithicoids, hominoids and hominids we have an entire branching and interlinked family history with all of the other life that shares our planet.

For any of that to make sense, that shared history would also have to be extraterrestrial, making the introduction billions of years ago at the very beginning of cellular life, and as such just adds more questions without actually answering anything.

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EarthSolar t1_j6boylv wrote

Reply to comment by LaRoara42 in Shouldn't goldilocks zones shift over time? by LaRoara42

When the Sun had just formed its luminosity was ~70% today’s, and so Earth back then would’ve received 70% its current light too. But the thing is, with carbon dioxide and other greenhouse gases, liquid water oceans can exist much further out than we are now. With just carbon dioxide the outer limit is around 40% Earth’s sunlight, so Earth has always been within the habitable zone.

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mfb- t1_j6botff wrote

Reply to comment by CubanHermes in Is there an upper limit to structure size in a vacuum? Could a sufficiently advanced civilisation build a galaxy sized structure in space or would it become too massive and collapse in on itself? by CubanHermes

You need cooling, not heating. The heat loss scales with the surface of the structure, but heat production scales with the volume (if we just scale everything up). The volume grows faster than the surface. Even the ISS needs radiators already.

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