Thousands of marchers streamed down Market Street on Saturday to demand greater public recognition of the economic and cultural benefits of science -- and to push back against funding cuts for scientific work on both the state and federal levels. Philadelphia police estimated that 10,000 people participated in the march, one of hundreds in the United States and abroad on Earth Day.

The marches were intended to voice alarm at growing public ignorance of — and even hostility toward — scientific research, and were billed by organizers as a nonpartisan event.

In Philadelphia, the demonstration soon took on a tone that was distinctly hostile to President Trump, with many marchers sharply criticizing the president's skepticism on global warming, support for fossil fuels, and cuts to funding of scientific research. They also denounced the president's support for religious organizations seeking exemptions from government rules that the groups say impede their religious beliefs.

"We know that human endeavors and only human endeavors can solve the problems that confront us," said Margaret Downey, president of the Freethought Society and one of the speakers at the rally. "We are concerned about those who want to tear down that Jeffersonian wall between church and state. Our message to Donald Trump should be: Don't tear down the wall of separation between religion and government."

Billed as the March for Science, the event began on the west side of City Hall, where thousands began to gather around 10 a.m., and then took off slowly down Market Street a short time later.

A festive atmosphere prevailed with marchers carrying signs reading "Science, not silence," "Invention = GDP," and "Don't be a fossil fool," among others. Periodically, the crowd erupted in chants, with a popular one being: "What do we want? Science. When do we want it? After peer review."

There were no signs of conflict. Only one Trump supporter was spotted alongside the march route, waving a flag reading "Make America Great Again," the Trump campaign slogan. Marchers angrily cursed at him, but there was no physical confrontation.

Upper Merion High School sophomore Maddie Harvey said she decided to attend with several of her classmates because she felt that the work of scientists has been denigrated by the Trump administration.

"We are appalled by the way this administration is handling evidence-based science," Harvey said. "There are so many scientists here, and what they do is based on facts -- and the administration is ignoring it."

Lynne Springer of Cherry Hill said the main takeaway from the march should be that voters won't tolerate Trump's proposed cutbacks on environmental regulation.

"Trump is about to kill our planet," she said.

With the president proposing steep cuts to the budget for the National Institutes of Health, which spends tens of billions annually on medical research at university labs around the country, a series of speakers at the conclusion of the march at Penn's Landing implored political leaders to continue government support. Otherwise, they said, the nation will face the loss of public benefits that scientific research brings in improved public health, greater economic growth, and prosperity.

Dr. Paul Offit, a teacher at the University of Pennsylvania's Perelman School of Medicine and coinventor of a rotavirus vaccine that has been credited with saving hundreds of thousands of lives, said funding for his research came from  NIH.

"We need to explain the value of science, in this age of antienlightenment, when science seems to be losing its position as a source of truth," he said

Denise Mauzerall, professor of environmental engineering and international affairs at Princeton University, said government efforts to halt climate change should be continued, despite Trump's support for fossil fuels.

"When I was a girl growing up in New York, winters were cold enough so that you could skate on ponds before Christmas," she said. "Now these ponds hardly even freeze at all."

Of climate changes underway, she said: "We are now certain that these changes are caused by human activity and we must act now to avoid devastating changes to our climate."

Midway through the speeches, a heavy rain broke out, and while several hundred remained to listen, most of the crowd of marchers quickly dispersed.