It will be easier to comprehend if you read it like this:-
Scientists have recently discovered what could be the largest and oldest living organism on Earth, a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilized spore some 10,000 years ago and extending for more than 30 acres in the soil of a Michigan forest.
"Scientists have recently discovered........a giant fungus.... (which was)spawned by a single fertilized spore some 10,000 years ago and (is)extending for more than 30 acres in the soil of a Michigan forest."
The use of "(is)extending" is because the giant fungus is still alive.
Originally Posted by Temico
I think I probably got your idea...
When we reduce a verb to its -ing or -ed form, we must look at one and only one thing: whether the noun that it will modify is the subject or object of that verb.
The -ing form is used for DOING the action, which means SUBJECT, which means ACTIVE voice.
The -ed form is used for RECEIVING the action, which means OBJECT, which means PASSIVE voice.
I guess the reason why nobody answers your questions is .......you tend to jump to unfounded conclusions!!
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