what are the criteria for scientist to consider a species extinct? maybe they just didnt search enough, like given the vastness of earth there r probably areas still unexplored?
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We have biologists that go out to the places where animal live and count how many of each kind they see. They do it in defined areas, and try to be as precise as possible. How you do it depends on whether you’re counting tiny things like bugs, or big things like giraffes, but there’s ways to get counts.
We watch the counts and compare them over months and years. If the number steadily decreases, and we don’t notice the animals moving to a new habitat, we pay special attention to counting them. We say that they are “threatened”. When the numbers have gone down a lot, we say that they are “endangered”. Eventually, we might not be able to find any more. It’s possible that there’s just a few, and they’re hidden and can’t be counted, but if after looking for them for years you don’t find any, you say “they’re extinct” (or, if there’s some in zoos, “extinct in the wild”).
We’re currently in the throes of a major extinction event called the “Holocene Extinction” or “Anthropocene Extinction”. Because of habitat destruction an pollution, the numbers of animals in the wild has been decreasing every year. At the moment, the number of animals (not species) is currently decreasing by about 50% every 40 years or so, about 1,000x the historical rate, which is why this is considered a major extinction event. Yet, we don’t have a real good handle on how many species go extinct each year as we can’t count them all, and we’re not fully aware of them all; we mostly notice when something big goes extinct, or a population suddenly crashes.
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