A new exhibit opening Thursday at the Smithsonian National Museum of Natural History showcases U.S. nature, geology and cultural traditions, all in celebration of the nation’s 250th anniversary. “From These Lands: Sharing Our Natural and Cultural Heritage” features 600 artifacts and specimens from 50 states, D.C. and five U.S. territories. The exhibition will be on view through December 2029. “Natural history is everything,” Kirk Johnson, the mu…